摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm.up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation.Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity.CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C.of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned.Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium.Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms.of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium.Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C.of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700603

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm.up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation.Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity.CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C.of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned.Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium.Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms.of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium.Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C.of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700610

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm.up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation.Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity.CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C.of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned.Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium.Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms.of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium.Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C.of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700615

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm.up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation.Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity.CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C.of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view.Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned.Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium.Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms.of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700622

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm.up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation.Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity.CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C.of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700626

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700629

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

630 THE ANALYSIS OF SWEETENED CONDENSED MILK I N Report of the Milk Products Sub-Committee to the Standing Committee on Uniformity of Analytical Methods MILK PRODUCTS. REPORT No. 3 THE ANALYSIS OF SWEETENED CONDENSED MILK IN WHICH THE SUCROSE HAS ALTERED DURING STORAGE THIS Sub-committee was convened by the Standing Committee and consists of the following members :-Nominated by the Government Chemist: Nominated by the London Chamber of Commerce E. R. Bolton F.I.C., M.I.Chem.E. A. L. Bacharach B.A. F.I.C. Ir. W. J. Pelle and J. Tavroges B.Sc., A.I.C. A. More A.R.C.S. F.I.C. Nominated by the Manufacturing Confectioners’ Alliance .T. Macara F.I.C. Nominated by the Society of Pablic Analysts and Other Analytical Chemists: G. D. Elsdon BSc. F.I.C. E. Hinks M.B.E.B.Sc. F.I.C. (Chairman) E. B. Hughes M.Sc. F.I.C. (Hon. See.) A. E. Parkes F.I.C. and J. D. Roberts B.Sc. Report No. 1 p. 2 ANALYST 1927 52, 403; Report No. 2 “The Determination of Sucrose in Sweetened Condensed Milk,” p. 10 ANALYST 1930 55 120) it was recommended that for the purpose of the Public Health (Condensed Milk) Regulations the percentage of total milk solids should be determined by subtraction of the percentage of sucrose from that of total solids. Such a procedure is admissible only when no material alteration has taken place in the sucrose and the recommendation in Report No. 2 contained the proviso “it being understood that the sample is a product prepared from milk and sucrose only and that it is in sound normal condition.” If any of the sucrose has been hydrolysed or has undergone other change total milk solids will be in error, any non-volatile derivative of sucrose being wrongly credited to milk solids.The present Report (No. 3) deals with certain decomposition products of sucrose their influence if present upon the determination of total milk solids as described in Report No. 2 and the means to be adopted in order to obtain the correct figure for total milk solids. As will appear later the total milk solids figure is not the only one to be affected by breakdown of the sucrose if decom-positioQ has proceeded in a certain direction the figure obtained for the remaining sucrose as determined by the polarisation process is also affected. Work on the matter which is the subject of this Report was begun in March, 1930.The problem to be solved was found to require the devising of new processes rather than the examination of established processes and selection of the best. The work carried out by the Committee can be divided into three stages: (i) Investigation of methods of determining small amounts of invert sugar in sweetened condensed milk. In the course of this work it was discovered that the change which occurs in the sucrose on keeping sweetened condensed milk does not usually result in the presence of invert sugar as such but that the laevulose fraction appears in part, as laevan. In previous reports (Milk Product WHICH THE SUCROSE HAS ALTERED DURING STORAGE 631 (ii) The second stage of the work involved the study of this change and the elaboration of methods for determining the products of the change so that the sucrose originally present could be calculated.The third stage developed into a simplification of Stage (ii) i.e. the development of a direct method which admits of a determination of the amount of sucrose originally present without carrying out the more lengthy procedure of Stage (ii) which however remains essential as affording an explanation of the change and providing if necessary a confirmation of the result obtained by the simplified process. (I) GENERAL (iii) The problem was viewed at first as being one solely of the detection and determination of invert sugar and processes were developed accordingly. During the course of this work however the observation was made that in a sweetened condensed milk in which the sucrose had been altered by prolonged storage the " apparent lactose " as determined by chloramine-T-iodide oxidation was higher than when determined by copper reduction; if invert sugar had been present the reverse should have been the case since chloramine-T-iodide does not oxidise laevulose.The only explanation of this observation appeared to be that assuming dextrose and laevulose to be present the dextrose exceeded the laevulose in amount but at the time there was no means of confirming this. Later on application of the Hinton and Macara process for the direct determination of laevulose2 to a sweetened condensed milk which had undergone extensive alteration on keeping it was found that although between 8 per cent. and 9 per cent.of sucrose had disappeared only about 0.5 per cent. of laevulose was present whilst chloramine-T-iodide oxidation again pointed to excess of dextrose over laevulose. These perplexing results were eventually found to be due to the formation of laevan. Nascent laevulose from sucrose is known to be condensed to laevan a gum,lO by the action of the levanase of certain micro-organisms 9 parts by weight of laevan being formed from 10 parts of laevulose. From a sweetened condensed milk which after storage exhibited this excess of dextrose over laevulose a laevan-forming organism was isolated and grown in pure culture. A preparation of laevan was made from a sucrose-peptone solution in which this organism was allowed to grow. This laevan was precipitated by 86 per cent.alcohol washed with alcohol and ether and dried. It was free from dextrose and laevulose and its [a] was found to be -50" calculated on the dry ash-free material. Laevan does not reduce cupric reagents and is less laevo-rotatory than laevulose. On treatment with acids (as for instance in the inversion process for the determination of sucrose) laevan is hydrolysed quantitatively to laevulose. Formation of laevan thus introduces considerable complication into the analysis of a sweetened condensed milk. In the first place the copper-reducing power of the serum is diminished proportionately to the amount of laevan formed; secondly the rotatory power of the serum is affected; and thirdly when the serum is inverted for the determination of sucrose the laevulose is re-constituted from the laevan and exhibits the same rotatory power and the same copper-reducing power as it would have done if no condensation to laevan had taken place.The optical rotation and the copper-reducing power of the " inverted " serum are therefore the same whether invert sugar has or has not been formed from the sucrose and whether laevan has or has not been formed either directly from the sucrose or from the laevulose fraction of invert sugar; they are the same as would have been shown by the inverted serum of the freshly prepared milk before any alteration in the sugars had taken place provided that formation of invert sugar 632 THE ANALYSIS OF SWEETENED CONDENSED MILK IN or of laevan laevulose and dextrose accounts for the whole of the altered sucrose.The optical rotation and copper-reducing power of the “ uninverted ” serum are, on the contrary affected according to the extent of laevan formation. Thus, when laevan is formed not only is the determination of altered sucrose affected, but the method for the determination of the remaining sucrose recommended by the Committee (Report KO. 2) is invalidated as would be any method depending upon acid inversion whether by polarisation or by copper reduction. It is clear therefore that it is of prime importance to ascertain in any given case first whether any alteration of the sucrose has taken place; and secondly, whether the altered sucrose appears in thc form of invert sugar or in that of a mixture of dextrose laevulose and laevan. From the examination of a number of old sweetened condensed milks (which had been kept in their original sealed containers) it would appear that formation of dextrose and laevulose with condensation to laevan of a considerable proportion of the laevulose is the usual direction in which sucrose is altered in those cases where any alteration at all has taken place.The analogous formation of dextran, by condensation of dextrose has not been observed though such a possibility should be borne in mind. It is important to note that no evidence was found of any alteration in the lactose even in an extreme case in which nearly 9 per cent. of sucrose as such had disappeared with the formation of much laevan. The possible presence of invert sugar of dextrose and of laevan must then, be taken into account in any critical analysis of sweetened condensed milk.In considering a scheme for such an analysis it is convenient to approach the more complicated issue of laevan through the simpler one of invert sugar. In a mixture of lactose sucrose and invert sugar all these should be deter-minable by a combination of polarimetric and suitable copper-reduction methods. The heating of milk however has a considerable effect upon the specific rotation, and some effect on the copper-reducing power of lactose. Though the temperature to which the milk is exposed during the manufacture of sweetened condensed milk does not appear to be high enough to have any significant effect the uncertainty attaching to this renders the determination of doubtful accuracy for small amounts of invert sugar.(11) COLORIMETRIC DETERMINATION OF INVERT SUGAR Some success was obtained with a direct qualitative and quantitative colorimetric process based upon the destruction of lactose by the method of Kruisheer3 and the colorimetric method of Kolthoff.* It was found that by chloramine-T-iodide oxidation of the serum (prepared by phosphotungstic acid clarification) lactose and dextrose could be eliminated and the laevulose determined colorimetrically by an alkaline 3-5-dinitro-salicylic acid reagent. This method was abandoned in favour of more satisfactory methods devised later. (111) THE BARFOED REAGENT Monier-William~,~ in a Report published by the Ministry of Health has worked out an application of Barfoed’s solution (copper acetate and acetic acid) to the detection and determination of invert sugar in sweetened condensed milk.This method has been fully studied by the Committee and in a modified form has supplied the basis of one of the processes recommended in this Report. (IV) MODIFICATION OF THE BARFOED REAGENT AND PROCESS When a mixture of Barfoed’s solution and serum prepared from sweetened condensed milk is heated reduction readily takes place if invert sugar is present. Even in the absence of invert sugar however a noticeable amount of reduction takes place increasing steadily with the time of heating. Monier-William WHICH THE SUCROSE HAS ALTERED DURING STORAGE 633 attributes this to hydrolysis of the sucrose by the acetic acid but the Committee finds that the lactose in the serum has a considerable reducing action upon Barfoed's solution.In the method described in the Ministry's Report5 a fresh milk serum con-taining sucrose is used as a control the reaction in the two serums-the one under examination and the control-being stopped when the control begins visibly to reduce the copper. The lactose effect is however sufficiently powerful to necessitate equal concentrations of lactose in the serum under examination and in the control serum. Variation in the proportion of lactose in condensed milk, and in fresh milk may be so large as to render any one fresh milk uncertain as a control for a given condensed milk. Attempts were made to destroy the invert sugar in one portion of the condensed milk serum by preliminary heat treatment with the Barfoed reagent, and to use the resulting serum (after filtration) as the control thus ensuring an approximately equal concentration of lactose in the control.This procedure did not give satisfactory results as the reducing power of the serum was greater after the preliminary treatment than before. In order to overcome these defects in the Barfoed method under discussion, experiments were made with the object of minimising the reducing action of lactose and so avoiding the necessity for the fresh milk control. It was found that by modifying the composition of the copper acetate solution, by reducing the temperature and by limiting and fixing the time for the reduction, the reducing action of lactose and of a milk serum free from invert sugar could be rendered negligible while a t the same time the reducing action of invert sugar could be maintained.First the addition of sodium acetate to the Barfoed reagent effects an improvement and causes the reduction to become more nearly a linear function of the amount of invert sugar present. This effect is not due to buffering of the reagent by the sodium acetate for determination of its neutralisation curve shows that true buffering does not occur. Secondly the rate at which sugars reduce cupric solutions depends for a given type of reagent upon the acidity or alkalinity of the solution and also upon temperature. Application of these principles enabled further improvement in the selective action of a Barfoed reagent to be effected. Moreover laevulose and dextrose are not equally reactive to Barfoed's solutions, the reduction by laevulose being the greater.By varying the proportion of acetic acid (in the presence of sodium acetate) the relative reducing powers of these two sugars may be altered. Diminishing the acetic acid causes their reducing powers to, approach equality but when this point is reached the lactose effect becomes unduly high. A compromise has therefore to be adopted. The reduced copper is best determined by the Bertrand procedure (solution in acid ferric sulphate solution and titration of the reduced iron with standard permanganate solution) and is conveniently expressed in terms of N/10 potassium permanganate solution. Table I shows the effect of varying the proportions of sodium acetate and acetic acid. All the reagents contained about 50grms.of crystallised copper acetate per litre the crystallised sodium acetate and acetic acid being varied as shown in this table. 70 ml. of the reagent and 25 ml. of a sweetened fresh milk serum,* alone and also with the addition of 1 ml. of a 2.5 per cent. solution of dextrose or laevulose were immersed in a bath at 80" C. for 20 minutes. *In these and subsequent experiments a sweetened fresh milk serum was prepared to simulate the serum of sweetened condensed milk by zinc acetate and potassium ferrocyanide clarification as described in Appendix I 100grms. of fresh milk and 16grms. of sucrose being used instead of the 40 grms. of sweetened condensed milk 634 Reagent 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. THE ANALYSIS OF SWEETENED CONDENSED MILK IN TABLE I Serum plus Serum plus Serum 25 mgrms.of 25 mgrms. of Sodium Acetic alone dextrose laevulose acetate acid 7 3 Grms. per M1. per N/10 potassium permanganate solution litre litre MI. M1. MI. 40 2 3.1 10.2 11.3 40 4 1.0 10.3 11-35 40 8 0.2 2.8 7.2 80 4 0.75 10.15 11-25 80 6 0.2 8.8 10-65 80 8 0.1 6.6 9.3 80 12 0.15 1-15 6.9 60 6 0.15 8.7 10.7 60 8 0.1 7.3 10.0 60 10 0.15 5.25 8.75 A Reagent 8 was adopted as being the most suitable; at 80°C. the lactose effect is negligible whilst the dextrose and laevulose effects are maintained at a high level. This reagent is hereinafter referred to as Modified Barfoed reagent. The reaction at the point at which the reducing action of lactose is negligible but at which laevulose and dextrose react sufficiently rapidly is very sensitive to temperature and to a less extent to time.The effect of temperature on the extent of the reduction by sweetened fresh milk serum is shown in Table 11. TABLE I1 70 ml. Modified Barfoed solution plus 25 ml. of sweetened fresh milk serum. Time of heating 20 minutes. N/10 potassium Temperature permanganate solution O c. MI. 78 0.1 80 0.2 82 0.8 The following curves show the reducing actions of laevulose and dextrose on the Modified Barfoed reagent at various concentrations and at three temperatures. The monose sugar was dissolved in 25 ml. of sweetened fresh milk serum. In Table I11 are given the results obtained with the Modified Barfoed reagent for laevulose dextrose and invert sugar the sugars being expressed as percentages of a sweetened condensed milk of ordinary composition; for the experiment these reducing sugars actually were added to 25 ml.of a sweetened fresh milk serum. TABLE I11 Temperature 80" C . ; time of heating 20 minutes. Monose sugar as per cent. of condensed milk Per Cent. Nil 0.1 0.2 0.3 0.5 1 *o 2.0 N/10 potassium permanganate solution for Laevulose M1. 0.15 (blank) 3-50 5.50 7-35 11-55 19.50 34-05 Dextrose MI. 0.15 (blank) 2.7 4-75 6.0 8.75 15.45 25-35 Invert sugar MI. 0-15 (blank) 2.8 4-25 6.15 9.85 18.0 29.4 WHICH THE SUCROSE HAS ALTERED DURING STORAGE 635 .=. 636 THE ANALYSIS OF SWEETENED CONDENSED MILK I N The most favourable conditions are :-(i) Heating in a large water-bath maintained at 80" C.(ii) Allowing the reaction to proceed for 20 minutes. Under these conditions a sweetened fresh milk serum has a negligible reducing action. Owing however to the sensitiveness of the reaction to temperature and also to a slight difference in reactivity of different preparations of the reagent, precise quantitative relations cannot be assumed from the above tables and curves. For accurate work it is necessary to standardise the reagent by using control serums containing approximately the same proportions of sugars as the serum under examination the controls being heated in the same bath as the serum being tested. By the use of this Modified Barfoed solution as little as 0.1 per cent. of invert sugar of dextrose or of laevulose in a condensed milk may readily be detected.Obviously the process will not indicate which of these sugars is present and a knowledge of the amount of either the laevulose or dextrose is necessary in order to interpret quantitatively the reduction obtained. The process has been of great service in establishing the nature of the changes occurring in the sucrose of sweetened condensed milk (as will appear later) and it takes its place in the recommendations of the Committee in this Report as providing a means of detecting whether or not any significant change has taken place in the sucrose. (V) INVERT SUGAR BY DIRECT DETERMINATION OF LAEVULOSE Hinton and Macara2 have developed a process for the determination of laevulose in sweetened condensed milk. It was intended to make this process the basis for the determination of invert sugar and if invert sugar were the only hydrolysis product of sucrose present the process would be perfectly valid.The application of this and of the chloramine-T and the Modified Barfoed processes to samples of altered sweetened condensed milk however demonstrated that the products of the altered sucrose were not dextrose and laevulose in equal proportions the dextrose being invariably in excess and it is therefore in-admissible to infer the amount of dextrose from a determination of the laevulose. Further investigation by means of the polarinietric readings combined with chloramine-T titrations on the serum before and after inversion indicated that some substance was present which was neither dextrose nor laevulose but which was converted into one of these during the inversion process.This substance as stated earlier proved to be laevan. Consequently neither the Modified Barfoed nor the Hinton and Macara process can be used by itself to determine the amount of altered sucrose. Nevertheless the determination of laevulose by- the latter process is necessary in the analysis of these altered samples when their detailed composition is required. This process has therefore been closely studied by the Committee. In the following table are given the results obtained in a series of analyses by this process by members of the Committee (A-H) using sweetened condensed milk from various sources with the addition of known quantities of invert sugar. Laevulose (added as invert sugar) as per cent.of condensed milk (-A 0.05 0.06 0.1 0.10 0.25 0.26 0.5 0-52 0.6 -1.0 1.00 TABLE IV Laevulose found Per Cent. I3 C D E F G H ' 0.06 0.06 - 0.06 0.06 0.03 0.06 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.27 0.26 0.26 0.26 0.25 0.26 0.26 0.55 0.50 0.52 0.62 0.54 0-51 0.53 1.00 0.99 1-10 1-02 1-06 0.91 1-03 - - - - - 0.60 WHICH THE SUCROSE HAS ALTERED DURING STORAGE 637 This process has been much used by the Committee during their investigations, and is recommended as quite satisfactory for the determination of laevulose. Full details of the process are given in Appendix 111. (VI) SUGARS AND LAEVAN BY THE MODIFIED BARFOED REAGENT As it appeared that in the altered sweetened condensed milks examined by the Committee a portion of the sucrose had been changed to dextrose laevulose and laevan it was at first thought to be necessary in order to ascertain the proportion of total milk solids to determine the various sugars and laevan.This was first attempted by use of the Modified Barfoed reagent in combination with the direct determination of laevulose and the determination of the specific rotation before and after inversion. The application of this method is best explained by means of an example. The amount of laevulose in the condensed milk serum (20 per cent.) was determined by the Hinton and Macara process and the serum was tested against a standard prepared by adding dextrose and laevulose to sweetened fresh milk serum. The amount of laevulose so added was arranged to be the same as that present in the condensed milk serum and the dextrose added was in the neighbour-hood of the amount expected in the unknown.The mixtures tested by the Modified Barfoed procedure were :-(1) 4 ml. condensed milk serum (this contained 0-0120 grm. laevulose). (2) 4 ml. sweetened fresh milk serum containing 0-0120grm. laevulose (3) 4ml. sweetened fresh milk serum. The titrations of the reduced copper were :-(1) 16-95 ml.; (2) 16-75 ml.; (3) 0-3 ml. of N/10 permaiiganate solution. Hence the net amounts due to laevulose and dextrose were:-(1) 16.65 ml.; (2) 16.45 ml. The laevulose in both of these solutions was the same in amount; hence since the titrations were so close the relative proportions of the dextrose and laevulose must have been very similar in both cases and it is sufficiently accurate to assume that the total amounts of the two sugars were directly proportional to the respective titrations.[Had the titrations lain further apart then for strict accuracy it would have been necessary to repeat the test with a more suitable amount of added dextrose in (2).] The total dextrose and laevulose in (2) being 0.0500 grm. the total in (1) is therefore and 0.0380 grm. dextrose. 0~0500 x - = 0-0505 grm. 16.45 But of this; 0.0120 grm. is laevulose ; therefore the amount of dextrose is 0*0385 grm., and the percentage of dextrose in the sample is 100 100 0.0385 x - x - x 0.9714* = 4.67 per cent. 4 20 The laevulose is 1.45 per cent. (direct determination). Hence the laevulose, converted into laevan is 4.67 - 1.45 = 3.22 per cent.and the laevan so formed is 3-22 x 0.9 = 2.90 per cent. * Volume of precipitate correction ; the specific rotations given in this example are corrected for volume of precipitate 638 THE ANALYSIS OF SWEETENED CONDENSED MILK I N The amount of sucrose present as such can obviously be determined if we subtract from the direct polarisation reading the rotations due to the laevan, laevulose and dextrose and from the invert polarisation reading that due to the inversion products derived from these substances. The values taken in this example for the specific rotations of dextrose, laevulose and laevan are corrected as far as is possible from available data for concentration effect of acid and salts etc. 4-67 - The part of the direct [a] due to dextrose = +52*7 x - - +2-46" 100 1-45 -100 , , , , , , , , laevulose =-93.0 x --1*35' 2.90-100 , , , , , , , , laevan = -50 X- - -1-45" Net effect -0.34' The actual direct [a] was + 29-75' and the direct [a] thus amended is therefore, +30*09".In the inverted solution the part of the [u]Eo due to these three constituents is the rotation of an amount of invert sugar equal to twice the amount of the dextrose that is, The actual invert [a] was -1*59' and the amended invert [a] is therefore +0*36". The sucrose present is then given by the change of [a]? on inversion divided by the inversion divisor factor 0.8825 ; thus sucrose The analysis thus gives :-Sucrose 33.68 per cent. Laevulose . . 1.45 , ,, Dextrose . . 4-67 9 9 ,, Laevan 2*90 JY J 9 (VII) SUGARS AND LAEVAN BY CHLORAMINE-T TITRATION On inversion of the condensed milk serum laevan is hydrolysed to laevulose, whilst dextrose and laevulose are unaffected.By determination of the specific: rotation and of the chloramine-T titration both before and after inversion, combined with a direct determination of the laevulose the amounts of all sugars and laevan can be calculated. This method again is best explained by an illustrative example. The particular milk the analysis of which is here recorded was at least two years old. Polarisatiort by the Committee's Report No. 2 method with zinc clarification. The analysis was conducted as follows:-[a]? Direct + 29-75" (corrected for volume of precipitate) Invert - 1.59" ( , Y 9 ,* , ) Lamdose by direct determination.1-45 per cent. (corrected for volume of precipitate) WHICH THE SUCROSE HAS ALTERED DURING STORAGE 639 Chzloramine-T titrations. Direct. Twenty ml. of this 4 per cent. serum taken for titration. Chloramine consumed (as N/20 thiosulphate) 23.67 ml. Invert. Forty ml. of 4 per cent. serum inverted neutralised and made up to 100 ml.; 20 ml. of this taken for titration. Chloramine consumed (as N/20 thiosulphate) 22.25 ml. A 20 per cent serum prepared by phosphotungstic acid clarification was diluted to 4 per cent. CALCULATION OF TRUE LACTOSE AND ORIGINAL SUCROSE. * From the (‘invert’’ titration: The correction for the effect of inversion etc. on lactose and other milk Hence the iodine equivalent to the lactose plus inverted sucrose is constituents (see Section VIII) = 0.15 ml.in this case. (22.25 - 0.15) x 0.006346 = 0.14025 grm., or expressed as per cent. of the sample 42-89 per cent. (corrected for volume of precipitate). The iodine equivalents of lactose hydrate and invert sugar under the conditions of this titration (see Tables XI11 and X of the original paperl) are 0.701 and 0.705 respectively. If L and S be the percentages of lactose hydrate and of sucrose in the milk before any alteration then for the fully inverted solution : Also from the invert polarisation : and from these two equations 0.701 L + (0.705 x 1.053 S) = 4249 0.524 L - 0.2195 S = - 1-59,? S = 43.47 and L = 15.15. Szccrose present at the time of analysis.-The (‘ invert ” chloramine titration, Then the sucrose present is calculated corrected as above mentioned is 22.10 ml.from the difference in thiosulphate titrations before and after inversion thus (2240 x - 23.67 x lo0 x 0-9786 = 33.09 0.741 0.8 (0.9786 being the volume of precipitate correction the factor converting 20 ml. of the solution titrated into 100 grm. of sample and 0.741 the sucrose factor taken from Table XV1). Note.-The dilutions and amounts taken for the chloramine titrations are not identical with those used for unchanged condensed milk as in the published process1; they had to be arranged so as to give suitable titrations in view of the extra-reducing sugar present. It is desirable to have the “direct” not very different from the “invert ’’ titration. It sometimes happens, as in this case that the titrations fall somewhat outside the range of the tables of factors given in the published paper; slight extrapolation is then required and is permissible.0.8 * The term “original sucrose” means the sucrose in the condensed milk before any alteration t See Section (VIII) formula (2). had taken place 640 THE ANALYSIS OF SWEETENED CONDENSED MILK I N Apparent Lactose.-From the “ direct ” titration a small correction has to be deducted for the slight absorption of iodine by the sucrose (see Table XIV of the original paper). In the present case this is 0.09 ml. and the corrected titration difference is thus 23.58 ml. Then the “apparent lactose” is Dextrose.-The difference between the true and apparent lactose (26.15- 15-15 = 11.00) represents the dextrose expressed as lactose hydrate Since dextrose has just twice the iodine-reducing power of lactose hydrate the actual percentage of dextrose is therefore 5.50.Laevan.-The difference between the dextrose and laevulose gives the amount of the latter which has been condensed to laevan which is therefore, 0.9 x (5.50 - 1.45) = 3.65 per cent. Sucrose 33-09 Lactose (anhydrous) 14.39 Laevulose . . 1-45 Dextrose . . 5.50 Laevan 3-65 The full analysis thus gives Per Cent. It will be observed that this scheme of analysis gives the lactose and is thus a more complete scheme for the determination of all sugars present than that described under Section VI though the latter has the advantage of providing a direct demonstration of the presence of reducing sugars other than lactose.As the result of various analyses carried out as above it became clear that by polarimetric and chloramine-T determinations using inverted serum it was possible to arrive at the amount of sucrose originally present in the milk. This being so a detailed determination of the various sugars and laevan is not necessary for the purpose of determining the percentage of milk solids. A simplified method of determining the original sucrose is given in the following Section (VIII) but where a determination of the various sugars and laevan is desired the most suitable scheme available is that described in this section (VII). (VIII) DETERMINATION OF ORIGINAL SUCROSE* BY POLARIMETER When sucrose which has become partly altered to dextrose laevulose and laevan (or to invert sugar) is inverted the product is invert sugar only and in the same quantity as would have been given by the original sucrose had none undergone alteration.Consequently after inversion of the sucrose of a sample of sweetened condensed milk the sugars in solution are lactose and invert sugar; and these two may obviously be determined by calculation from the results of two independent quantitative measurements of these two sugars e.g. by polarisation and measurement of reducing power towards copper or iodine (using chloramine-T) . Examples of analyses by polarisation and copper-reducing power of the inverted serum are given later (see Table VII). The Committee found, however the most suitable and reliable reduction method to be the chloramine-T method.This method was studied by the Committee during the preparation of Report No. 2 and was then found to give slightly higher results for sucrose than those obtained by the polarimetric method recommended in that report the accuracy of AND CHLORAMINE-T-IODIDE OXIDATION * See footnote Section VII page 639 WHICH THE SUCROSE HAS ALTERED DURING STORAGE 64 1 which in the absence of hydrolysis products was fully established. It has since been found that this error is due to a slight absorption of iodine by non-sugar constituents of the inverted milk serum as shown by experiments carried out on the following lines :-Sweetened fresh milk serum* containing a known amount of sucrose and also, sucrose mixed with clarified fresh milk were subjected to the chloramine-T process before and after inversion.In the absence of any effect produced by the milk serum constituents the amount of reagent absorbed in the inverted solution should be the sum of the amount used in the uninverted solution due to lactose plus the amount calculated from the tables in the paper1 due to the inverted sucrose. This however was found not to be the case the results obtained from the inverted solutions being invariably higher by a small amount. The discrepancy was found to vary directly with the proportion of milk solids in the serums the absorption of iodine by the non-sugar non-precipitated milk constituents being found to be equivalent to 2.2 ml. N/20 thiosulphate solution per 1 grm. of fat-free milk solids. Hence it is possible to apply a correction to the titration results on the inverted serum to compensate for this effect.In the analysis of a condensed milk by the chloramine-T method the amount of fat-free milk solids represented by the quantity of serum taken in the test is approximately 0.07 grm. and the correction to be applied to the titration is therefore 0.15 ml. N/20 thiosulphate solution. If other dilutions are taken or abnormal samples (as regards fat-free solids) are in question this figure can be adjusted to accord with the amount of fat-free solids corresponding to the volume of serum taken. When this correction is applied the chloramine-T method gives the true sucrose. In the following table is given the analysis of a fresh sweetened condensed skim milk: TABLE V Per Cent.Sucrose by chloramine-T process . . 43.40 Lactose (anhydrous) . . 14-88 Dextrose 0.01 Laevulose 0.02 Direct calculated + 36.96" DO. [a]:' found + 37-05", Sucrose by Committee's RePort No. 2 method 43.40. Directions for the process are given in Appendix IV. The derivation of formulae there employed is as follows:-The serum prepared by zinc acetate and potassium ferrocyanide clarification is a 20 per cent. solution of the condensed milk; this becomes a 16 per cent. solution after inversion. A suitable dilution of this serum is 20 ml. made up to 250 ml. of which 25 ml. is taken for chloramine-T titration. The phosphotungstic clarification is however to be preferred for the chloramine-T process and for this a 5 per cent. solution of condensed milk is clarified; 25 ml.of this are inverted and made up to 100 ml. Twenty-five ml. of this dilution are taken for the chloramine-T titration (in both cases the dilutions must be neutralised as described in Appendix IV). Let R = [a]? of the inverted solution (zinc clarification); E = grms. of iodine consumed by 100 grms. of sample after inversion; n = titration-difference in ml. N/20 thiosulphate. V = volume in ml. to which the sample is diluted before filtration; v = correction in ml. for volume of precipitate produced during clarification. * See footnote page 633 642 THE ANALYSIS OF SWEETENED CONDENSED MILK I N (The titration-difference (n) has to be corrected for absorption by non-sugars; this correction as shown above is usually -0015ml.) 250 100 100 V-v Then E (zinc serum) = (n - 0.15) X 0.006346 X - 2 5 ' 2 0 ' 1 6 63.46 V-v 32 V = (n - 0.15) x - -and E (phosphotungstic acid serum) 100 100 100 v-v V 2 5 x ? % ? x 5 - = (n - 0.15) x 00006346 x -v-v = (n - 0.15) x 63-46 x 0.032 x - V Now with the dilutions suggested the factors for lactose hydrate and invert sugar (1.053 x sucrose) in grms.of iodine per 1 grm. of sugar are 0-702 and 0,706, respectively. Hence if L and S be the percentages of lactose hydrate and of original sucrose, respectively we have 0.702 L + 0.706 x 1.053 S = E. (1) The specific rotations [u] in the inverted zinc serum of lactose hydrate and of inverted sucrose are 52.4' and -21*95O respectively. Hence 0.524 L - 0.2195 S = R. (2) From equations (1) and (2) S = 0.964 E - 1-29 R and L = 0.404 E + 1.37 R Thus from the two operations of determining the specific rotation and the chloramine-T titration of the inverted solution the percentage of original sucrose is obtained.Chloramine-T titrations obtained on the zinc clarified serum tend to be a little low. This appears to be connected with the precise conditions of alkalinity. As this difficulty does not occur with the phosphotungstic clarified serum the latter is advised though the zinc clarified serum can be used as a preliminary if desired. TESTS OF THE PROCESS ON OLD CONDENSED MILKs.-Refiort No. 26 (Tables I1 and 111) contains the results of analyses by members of the Committee of samples of specially prepared condensed milk. These analyses were made in November and December 1929.One tin of each of these batches was reserved and in March 1932 was analysed by the above method with the following results: A. Table I 1 Milk. Appearance on opening Normal. Polarisation. Direct [a] on sample + 34-28'. Original sucrose from invert polarisation and chlora-Average figure as published in Repmt No. 2 for sucrose Note.-Very little alteration of the sucrose had taken place in this milk. Invert [a3? , ? - 3-15'. mine-T (both on zinc serum) . . . . 42.39 per cent. 42.54 per cent WHICH THE SUCROSE HAS ALTERED DURING STORAGE 643 B. Tnble 111 iWiEk. Appearance on opening Showed brownish discoloration and thickening. Polarisation. Original sucrose from invert polarisation (zinc clari-fication) and chloramine-T (phosphotungstic clarification) .. 44.56 per cent, Original sucrose from invert polarisation and chloramine-T (both zinc clarification) . . . . 44.16 per cent. Average figure as published in Report No. 2 for sucrose 44-52 per cent. Direct [a] on sample + 33-93". Invert [a]? 8 9 ) - 2.32". Note.-The polarisation in March 1932 points to an alteration of about 4 per cent. of sucrose. Six tins of another preparation which had been kept for a considerable time and which on opening exhibited varying signs of alteration the milk being dis-coloured and thickened were mixed and distributed to members of the Committee. The samples were analysed in the various laboratories by this method with the following results: TABLE VI Laboratory A B C D E F G Original sucrose Per Cent.42-80 42.94 42-68 42.90 42.63 42.99 42-73 Mean 42-81 0.18 0.11 Maximum deviation from the mean Mean deviation from the mean As mentioned at the beginning of this section original sucrose can be deter-mined by combination of polarimetric measurement of the inverted solution and the reducing action of the inverted solution towards copper solution or chloramine-T. The chloramine-T method is the one recommended but by the use of copper solution satisfactory results have been obtained. The Lane and Eynon method' was used for determining the copper-reducing power solutions containing lactose and invert sugar in approximately the proportions which would be obtained from a normal condensed milk in similar dilution being used as a control thus giving a comparison for reference to Lane and Eynon's tables.It is not necessary to describe the method in detail but the results obtained by it are included in Table VII with those obtained by the chloramine-T and Modified Barfoed methods The analyses recorded in this table are those of old sweetened condensed milks more or less altered during storage and they afford confirmation of the view that dextrose laevulose and laevan formation is the usual and in the experience of the Committee the only, change which takes place in the sucrose. In these analyses the laevulose was determined in all cases by the Hinton and Macara process and in the analyses with Modified Barfoed reagent the lactose figure is taken from the chloramine-T analyses 644 THE ANALYSIS OF SWEETENED CONDENSED MILK I N TABLE VII Milk A Chloramine-T and polarisation Per Cent.Method after inversion Sucrose . . 33-09 Lactose (an hydrous) 14-39 Dextrose . . . . 5-50 Laevulose . . 1.45 Laevan . . 3.65 Direct calculated . . +29.60" found . . +29*75" Original sucrose calcu-lated from the above figures . . 43-54 Modified Barfoed and polarisa-tions before and after inversion Per Cent. 33.68 14.39 4.67 1 -45 2.90 +29*93" + 29.75" 42-56 Milk C 7-Sucrose . . . . 33-29 Lactose (anhydrous) 11.21 Dextrose . . . . 4-33 Laevulose . . . . 1-66 Laevan . . 2.40 Direct [a]:o calculated . . +2i*79" found . . +27*63" Original sucrose calcu-lated from the above figures . . . . 41.51 33.25 11.21 4.03 1-66 2.13 +27*74" + 27.63" 40.91 Milk B A I 1 Chloramine-T and polarisation after inversion Per Cent.30.83 14.94 7-15 1.72 4.89 +28.38" +27*21 " 44.42 Modified Barfoed-and polarisa-tions before and after inversioii Per Cent. 29.41 14.94 7.21 1 -72 4.94 +27*44" +27.21" 43.11 Milk 1) P 35-40 35.95 11-44 11-44 2-75 2.09 1.86 1.86 0.80 0.21 +29*11 " +29*41 " +29*26" +29*26" 40.63 39-92 Milk E Sucrose . . Lactose (anhydrous) . . Dextrose . . Laevulose. . . Laevan Direct [a] calculated . . found I Ch loramine-T and polarisation after inversion Per Cent. 31.80 11.92 4.68 0.57 3.70 +27.75" +27*7l0 Original sucrose calculated from the above figures .. 40.69 I Copper reduction (Lane and Eynon) and polarisation after inversion Per Cent. 32-08 11-99 4-51 0.57 3.55 +27*95O +27*71° 40.6 WHICH THE SUCROSE HAS ALTERED DURING STORAGE 645 Milk F Method Sucrose . . Lactose (anhydrous) Dextrose . . Laevulose . . Laevan Direct [u]zo calculated found Chloramine-T and Lane and Eynon and polarisation polarisat ion after after inversion inversion Per Cent. Per Cent. 32-26 33-04 14-46 14-40 6.15 5-60 1.6'7 1.67 4.03 3.54 . . +29*04" +29*48" +29*14" +29.14" Modified Barf&d and polarisation before and after inversion Per Cent. 32.65 14.46 5.60 1.67 3-54 +29-26" +29*14" Original sucrose calculated from the above figures . . 43.95 43.68 43.29 Milks A B and F were of the same brand and probably from the same batch, Milks C D and E were of another brand and were probably of the same batch.E was analysed in January 1931 C in September 1931 D and A in December, 1931 B and F in January 1932. It is interesting to note that a sample of the same make and again probably of the same batch as A and F was analysed in September 1929 before some of the processes used later had been devised; the analytical results obtained then have been recalculated as far as possible in the light of the more recent work and are as follows: Sucrose . . . . 37.61 from chloramine-T and invert polarisation Lactose (anhydrous) . . 15-02 Do. Dextrose . . 3.18 Laevulose . . 0.44 from Lane and Eynon method. Laevan 2.47 Direct [u]zo calculated .. +33.25" Original sucrose calculated from the above figures . . Per Cent. determinations. found +33*22" 43.66 The analyses show that in September 1929 about 6 per cent. of sucrose had broken down and that the action continued (in the original sealed tins) until by January 1932 between 11 and 12 per cent. of sucrose had disappeared with progressive formation of larger and larger quantities of dextrose laevulose and laevan. During the course of this work many sweetened condensed milks of commerce have been examined. It would seem that only when freshly prepared are these free from hydrolytic products of sucrose ; amounts of these products corresponding with 0.2 to 0.5 per cent. of altered sucrose are common although the milk is apparently quite sound.(IX) It has been shown that after extensive alteration of the sucrose the percentage of sucrose originally present can be determined. The total solids however will be determined with the altered sucrose present. In so far as sucrose is converted into invert sugar the total solids will be higher than the original total solids, DETERMINATION OF TOTAL MILK SOLIDS IN ALTERED SWEETENED CONDENSED MIL 646 THE ANALYSIS OF SWEETENED CONDENSED MILK IN 1 part of sucrose giving 1.053 part of invert sugar. On the other hand in so far as the laevulose is condensed to laevan there is a loss of total solids 1 part of laevulose giving 0.9 part of laevan. If all the laevulose is converted into laevan, the loss by condensation is equal to the gain by hydrolysis.In any of the cases investigated by the Committee there would have been on balance a slight increase of total solids resulting in a slightly higher figure for total milk solids if these are obtained by subtraction of the " original sucrose " from total solids as determined. The error giving a slight credit to total milk solids may be neglected. RECOMMENDATIONS That for the purpose of the Public Health (Condensed Milk) Regulations (it being understood that the sample is a product prepared from milk and sucrose only) : I. Sweetened condensed milk should be examined by the Modified Barfoed process described in -4ppendix I1 to this report; 11. If no significant alteration is disclosed by this examination the per-centage of total milk solids should be determined by subtracting the percentage of sucrose determined by the method recommended in Report No.2 from the percentage of total solids determined by the method described in Report No. 1; If significant alteration is disclosed the percentage of total milk solids should be determined by subtracting the percentage of original sucrose determined as described in Appendix IV to this Report from the percentage of total solids determined by the method described in Report No. 1. 111. APPENDIX I PREPARATION OF SERUMS PREPARATION OF SAMPLE.-Mix the sample as in the manner prescribed in Report No. la. ZINC ACETATE - POTASSIUM FERROCYANIDE SERUM* REAGENTS.-&ZC Acetate Solution.-~1.9 grms. of crystallised zinc acetate, Potassium Ferrocyanide SoZution.-lO*6 grms. of crystallised potassium ferro-Concentrated Ammonia Solution nominal S.G. 0.880. Dilute Ammonia Solutiout.-lO ml. of concentrated ammonia solution diluted with water to 100ml. Dilute Acetic Acid SoZution approximately equivalent to the dilute ammonia solution. PROCEDURE.-Tra.nSfer to a 100 ml. beaker an accurately weighed quantity, approximately 40 grms. of the well-mixed sample; add 50 ml. of hot distilled water (80"-90" C . ) ; mix; transfer to a 200 ml. measuring flask washing in with successive quantities of distilled water at 60" C. until the total volume is from 120 to 150ml. Mix; cool to air temperature and then add 5ml. of the dilute ammonia solution. Add a sufficient quantity of the dilute acetic acid solution to neutralise the ammonia added (the exact equivalent is determined beforehand by titration) and again mix.2n(C2H,O2), 2H20 and 3 ml. of glacial acetic acid in water made up to 100 ml. cyanide in water made up to 100 ml. Again mix and then allow to stand for 15 minutes. * This is the same serum as is used for the determination of sucrose according to Report The procedure for determining the specific rotation of the inverted serum (Appendix IV) No. 2. is identical with that described in that Report WHICH THE SUCROSE HAS ALTERED DURING STORAGE 647 Add with gentle mixing 12.5 ml. of zinc acetate solution and mix followed in the same manner by 12.5 ml. of potassium ferrocyanide solution. Bring the contents of the flask to 20" C. and add distilled water (at 20" C.) up to the 200 ml. mark. Up to this stage all additions of water or reagents should be made in such a manner as to avoid formation of air bubbles and with the same object in view all mixings should be made by rotation of the flask rather than by shaking.If bubbles are found to be present before completion of dilution to 200 ml. their removal can be assisted by temporary attachment of the flask to a vacuum pump and rotation of the flask. ,4110~ to stand for a few minutes and then filter through a dry filter paper rejecting the first 25ml. of filtrate. Close the flask with a dry stopper and mix thoroughly by shaking. This serum is used for (a) Modified Barfoed method. (Appendix 11.) (b) Determination of [a]EO of inverted solution. (,Appendix IV.) (c) If desired for approximate chloramine-T titration.(Appendix IV.) (d) Determination of laevulose. (Appendix 111.) PHOSPHOTUNGSTIC ACID SERUM REAGENT.-PhosphotzCngstic Acid Precipitant. 50 grms. of crystalline sodium tungstate N%WO4,2H,O and 6 grms. of crystalline disodium phosphate are dissolved in about 200ml. of distilled water and 220ml. of 2 N hydrochloric acid solution (or the equivalent amount of acid of other normality) are added slowly with stirring. The solution is diluted to 500 ml. and filtered. The acidity of the reagent should be so adjusted that 20ml. require approximately 16.0ml. of N/2 sodium hydroxide solution when titrated with methyl orange as indicator, and the 9 of the reagent diluted to five times its volume with water is ap-proximately 1.3. PROCEDURE.-Transfer to a 200 ml. measuring flask an accurately weighed quantity of 10 grms.of the well-mixed sample by successive quantities of distilled water at about 60" C. using about 120 ml. of water in all. Mix; cool to air tem-perature and add with gentle mixing 10 ml. of the phosphotungstic acid reagent. Bring the contents of the flask to 20" C. and add distilled water (at 20" C.) up to the 200ml. mark. Up to this stage all additions of water or reagents should be made in such a maflner as to avoid formation of air bubbles (see under zinc acetate and potassium ferrocyanide serum above). Close the flask with a dry stopper and mix thoroughly by shaking. Allow to stand for 10 minutes and then filter through a dry filter paper rejecting the first 25 ml. of filtrate. (In the case of small samples the full quantity given above may not be available.If the prescribed quantity of 10 grms. is departed from the amount of the phospho-tungstic acid reagent must be varied so that its volume in ml. is numerically equal to the weight of sample taken in grms. The calculation in Appendix IV [ii] for the phosphotungstic acid serum holds only when this relationship is maintained and for a 5 per cent. serum.) This serum is used for the chloramine-T titration. APPENDIX I1 MODIFIED BARFOED PROCESS REAGENT.-cOfifiei SoZ.utiort.-Dissolve 60 grms. of crystallised sodium acetate in water add 105 ml. of N/1 acetic acid and make up to 1 litre with water 648 THE ANALYSIS OF SWEETENED CONDENSED MILK IN Transfer to a dry bottle add 52grms. (or more) of finely powdered crystallised copper acetate and shake to saturation.Ferric Sulphate Solution.-Dissolve 50 grms. of ferric sulphate in about 400 ml. of water to which 109 ml. of concentrated sulphuric acid has been added. Make up to 1 litre with water and filter. Before use this solution should be treated with N/10 permanganate until the colour of the latter ceases to be discharged. Filter. N/10 Potassium Permanganate Solution. PROCEDURE.-Introduce 25ml. of serum (zinc serum Appendix I) into a thin-walled boiling tube (internal measurements 8 x 14 inches); add 70 ml. of the copper solution ; mix ; cover the tubes with a watch-glass and immerse to the level of the liquid in the tube in the water in a large water-bath maintained at 80" C. for 20 minutes. Remove ; cool in running water; filter on asbestos by suction and wash the tube and filter containing the cuprous oxide rapidly a few times with freshly boiled distilled water rejecting the filtrate and washings.Dissolve the cuprous oxide (including any remaining in the tube) in 20 ml. of the ferric sulphate solution; wash the asbestos pad with cold freshly-boiled distilled water adding the washings to the ferric sulphate filtrate and titrate with N/10 permanganate to faint permanent pink.* Note.-A convenient asbestos filter may be prepared by inserting a loosely fitting glass bead into the neck of a Allihn filter tube; above the bead is placed a layer of glass wool and on this is laid the asbestos which is added as a wet pulp and drawn on to the glass wool by suction. Solution of the cuprous oxide is rapidly effected by pipetting the ferric sulphate solution into the reduction tube transferring to the Allihn tube and thoroughly mixing the surface asbestos layers with the sulphate solution by means of a flat-ended glass rod leaving the lower asbestos layers and the glass wool undisturbed.APPENDIX I11 HINTON AND MACAKA PROCESS FOR DETERMINATION OF LAEVULOSE2 REAGENTs.-Sucro.se Solution.-Approximately 9 grms. per 100 ml. (freshly Iodine Solzttion.-l3 grms. of iodine and 15 grms. potassium iodide per Mixed Alkali Solution.-Equal parts of 2 N sodium carbonate and 2 N Sulphuuric Acid.-Approximately 5 A'. Sodium Sulphite Solzdion.-20 per cent. w/v. Dilute Sodium Sulphite Solution.-2 per cent. freshly prepared ; or diluted from the 20 per cent.solution. L ~ f l ' s So1ution.Dissolve 25 grms. of crystallised copper sulphate in 100 ml. of water; 50 grms. of citric acid in 50 ml. of water; 388 grms. of Na2C0, 10H,O in 300 or 400 ml. of luke-warm water. Add the citric acid solution to the sodium carbonate solution and then add the copper solution. Mix cool make up to 1 litre and filter. Note.-This solution should be accurately prepared and 10 ml. of the finished solution should require approximately 45 ml. of N / 2 sulphuric acid for neutralisation to methyl orange. * If the titration exceeds about 15 mls. NllO KMnO the test should be repeated with a SUibdbk? quantity of serum made up t o 25 ml. For specially accurate work this dilution should be made with a serum prepared from fresh milk and sucrose.prepared). 100 ml. sodium hydroxide WHICH THE SUCROSE HAS ALTERED DURING STORAGE 649 Iodate-iodide Soldion.-2.7 grms. of potassium iodate 30 grms. of potassium Potassium Oxalate Solution.-A saturated aqueous solution. Sodium Tlaiosulphate Solution.-N/20. Soluble Starch Solution.-Approximately 2 per cent. Control Serum.-Prepared from fresh milk using 100 ml. of milk with the same quantities of ammonia and acetic acid and precipitants as for 40 grms. of condensed milk made up to 200 ml. and filtered. PRocEDuRE.-(i) Oxidation of the AZdose Sugars.-Pipette 10 ml. of the prepared condensed milk serum (zinc serum Appendix I) and the same amount of the control serum into 250ml. conical flasks ensuring that the liquid does not flow on to the sides of the flasks.To the condensed milk serum add 10 ml. of water and to the control serum 10ml. of the sucrose solution. Note.-Some workers find it preferable to add 2 ml. of a 0-5 per cent. solution of invert sugar to each serum so as to ensure a perceptible reduction in the control; this is termed " sensitising invert.'' Such addition makes no difference to the subsequent procedure. To each then add exactly 6 ml. of the iodine solution and exactly 6 ml. of the 2 N mixed alkali solution; mix gently and allow the flasks to stand for 10 minutes at from 18" C. to 20" C. Acidify with 1.6 ml. of 5 N sulphuric acid and remove the liberated iodine first with 20 per cent. sodium sulphite solution and finally, after adding 6 drops of soluble starch solution with the 2 per cent. sulphite solution.(This operation should have the precision of a titration though the quantities of sulphite solution needed are not measured; it should be conducted as rapidly as possible.) When all free iodine is eliminated immediately add one drop of methyl orange solution and neutralise with the 2 N mixed alkali solution. Note.-The time elapsing between acidifying with 5 N sulphuric acid and neutralising with the mixed alkali should not exceed 2 minutes to avoid the danger of inversion of the sucrose. (ii) Treatment with Lufs Solution.-To the contents of each flask add 20 ml. of Luff's solution; cover with a watch-glass and heat the contents to boiling on a plain wire gauze over a burner regulated so that boiling takes place in 2 minutes; impinging of the flame or hot gases on the sides of the flask should be prevented by an asbestos sheet with central hole of suitable dimensions placed in contact with the wire gauze.When boiling takes place transfer the flask to an asbestos-covered gauze already heated by a small Bunsen flame attaching a reflux condenser, and maintain gentle ebullition for exactly 10 minutes. iodide and 10 ml. of A7/2 sodium hydroxide solution per litre. Remove from the flame and cool in running water for four or five minutes. Titration of the Reduced Cop+er.-Add exactly 25 ml. of the iodate-iodide solution and 20 ml. of saturated potassium oxalate solution. Acidify carefully, while swirling with 20 ml. of 5 N sulphuric acid. Shake round (with some care, as frothing occurs) until the precipitate of cuprous oxide (which is partly con-verted into white cuprous iodide) has dissolved and titrate with N/20 thiosulphate.No further addition of starch should be required. The end-point is distinguished by a sharp change to a fine light blue (the colour of the cupric salt). Calculation of the LaevuZose.-The difference between the titrations of the sample serum and the control serum as ml. of N/20 thiosulphate solution, multiplied by 0.064 gives the percentage of laevulose in the sample uncorrected for the volume of the clarification precipitate. (This factor is strictly correct only for a 20 per cent. serum i.e. if exactly 40 grms. of condensed milk was diluted to 200 ml. in the preparation of the serum.) The correction for volume of precipitate, if required is calculated as in Appendix IV i 650 THE ANALYSIS OF SWEETENED CONDENSED MILK I N APPENDIX IV THE DETERMINATION OF '' ORIGINAL SUCROSE " (i) SPECIFIC ROTATION OF THE INVERTED SERUM KEAGENT.-~ydroch~oric Acid Sohtion = 6.34 times normal.IsvERsIoN.-Pipette into a 50-ml. measuring flask 40ml. of the filtrate obtained by zinc clarification (see Appendix I ) ; add 6 ml. of 6.34 N hydrochloric acid. Immerse the entire bulb of the flask for 12 minutes in a water-bath maintained at 60" C. mixing by rotatory movement during the first three minutes, in which time the contents of the flask should have attained the temperature of the bath. Cool and make up to the 50 ml. mark at 20" C. with distilled water; mix, and allow to stand for one hour. INVERT POLARISATION.-Determine the rotation at 20" c.CALCULATION. W= F = P = V = v = I = 1 = *R = weight of sample taken in grms. percentage of fat in the sample, volume (in ml.) to which the sample is diluted before filtration, correction in ml. for volume of precipitate produced during clarifica-. observed invert polarimeter reading, length in dm. of polarimeter tube, specific rotation of the inverted serum ( [ a ] 3 , Y Y , protein (N x 6.38) in the sample, tion, * Note.-If the mercury green line is used instead of the D line the. reading should be multiplied by 0.847 to convert to rotation for the D line. W 100 then v = - [(F x 1-08) + (P x 1*55)], v-v v and R = (3 x I) x - x - v 1XW (ii) THE CHLORAMINE-T TITRATION REAGENTS.-N/Bo Chloramilze-T Solutio?z.-Containing 7.04 grms.per litre,, freshly prepared and protected from light. Standard Sodium Thiosul'hate Solution.-Preferably rather stronger than N/20 so that 50 ml. of the chloramine-T solution can be titrated without refilling a 50ml. burette. Note.-The thiosulphate must be accurately standardised against pure potas-sium dichromate by the method of Popoff and Whitman.9 The procedure is as follows: To 25 ml. of N/10 potassium dichromate solution add 20ml. of 10 per cent. potassium iodide solution and 10 ml. of 2 N hydrochloric acid; stopper the flask and allow to stand in the dark for 10 minutes; then titrate with the thiosulphate. N/2 Sodium Hydroxide Solution. N/10 Sodium Hydroxide Solution. Solubte Starch So1utio.n.-Approximately 2 per cent WHICH THE SUCROSE HAS ALTERED DURING STORAGE 661 PRocEuuRE.-lnversion.-Pipette 25 ml.of the phosphotungstic acid serum (see Appendix I) into a 100-ml. measuring flask add 15 ml. of distilled water and 5 ml. of 6-34 N hydrochloric acid. Immerse for 12 minutes the entire bulb of the flask in a water-bath maintained at 60" C. mixing by rotatory movement during the first 3 minutes in which time the contents of the flask should have attained the temperature of the bath. Cool add N / 2 sodium hydroxide solution continually mixing until neutral carrying the addition of alkali to the point of a definite turbidity (no internal indicator should be used). Cool and make up to the 100 nil. mark at 20" C. with distilled water. Titration of inverted and neutralised Serum.-Into one of two 250 ml.flasks or bottles pipette 25 ml. of the inverted neutralised serum which has been diluted to 100 ml.; into the other pipette 25 ml. of water (as a blank). To each add 3 ml. of N/10 caustic soda solution followed by 20 ml. of 10 per cent. potassium iodide solution then into each pipette accurately 50 ml. of the N/20 chloramine-T solution; close the flasks or bottles and leave in the dark for 18 hours at a tem-perature of from 17" to 18" C. At the end of this time add to each flask 10 ml. of 2 N hydrochloric acid and titrate at once with the thiosulphate solution with starch solution as indicator. Note.-All measuring flasks pipettes and burettes must be accurately cali-brated special attention being paid to drainage of the burette which should be calibrated in the manner in which it is used for the titration.Readings of the burette are made to 0.01 ml. CALCULATION. S = E = w= F = P = V = v = n = percentage of " original sucrose " in the sample, iodine absorbed per 100 grms. of sample, weight of sample taken in grms., percentage of fat in the sample, percentage of protein (N x 6.38) in the sample, volume (in ml.) to which the sample is diluted before filtration, correction in ml. for volume of precipitate produced during clarifica-difference between the inverted serum and the blank titrations in tion, ml. N/20 thiosulphate solution. Then for calculation of the original sucrose, W 100 v = - [(F x 1-08> + (P x 0.74) + 3-75] ml. E = (n - 0*15*) x 63-46 x 0.032 x 'Zv V and S = 0.964 E - 1.29 R.Addendum.-If it is desired to determine the chloramine-T figure on the zinc serum the procedure is as follows:-Pipette 20 ml. of the inverted serum (which has been used for the determination of [a]? invert) into a 250-ml. flask add N/2 sodium hydroxide solution with continual mixing (approximately 31 ml. will be required) until neutral neutrality being shown by a distinct perrnanent turbidity. *This is the correction for absorption by non-sugars and applies only to the quantities prescribed and for a usual proportion of non-fatty solids in the milk 652 NOTES FROM THE REPORTS OF PUBLIC ANALYSTS Make up to the 250-ml. mark at 20" C. with distilled water and mix. this solution are taken for the chloramine-T titration. 25 ml. of Then 63.46 V-V 32 V E = (n - 0.15) x - x -and as before S = 0.964 E - 1.29 R. (These formulae for the zinc serum apply strictly only to a 20 per cent. serum, i.e. if exactly 40 grms. of condensed milk was diluted to 200 ml. in the preparation of the serum.) As explained in the body of the Report results obtained on the zinc serum are approximate only and slightly low. Note.-The volume of precipitate corrections are based upon the data recorded in Report No. 2 (THE DETERMIXATION OF SUCROSE IN SWEETENED CONDENSED MILK). 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES ANALYST 1927 52 668. 1931 56 286. 2. fnters. Lebensm. 1929 58 No. 3 261. International Sugar .J. 1923 25 662. Ministry of Health Reports on Public Health and Medical Subjects No. 57. ANALYST 1930 55 119 and 120 Tables I1 and 111. J. SOC. Chew. Ind. 1923 42 3 2 ~ 1 4 3 ~ and 4 6 3 ~ ; 1927 46 434-435~. ANALYST 1927 52 402. J . Amer Chena. Soc 1925 47 2275. J . Ind. Eng Chem. 1911,3 481. J . Biol. Chem. 1920,43 171. J . SOC. Chem. Ind., 1902 21 1381. For and on behalf of the SNb-Committee, (Signed) E. HINKS (Chairman) , E. B. HUGHES (Hon. Secretary) July 193

ISSN:0003-2654    

DOI:10.1039/AN9325700630

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN932570652b

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic.This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm.of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased.The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700653

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm. Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected.The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected. Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results.The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm. in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable.The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.294 EVERS: THE DETECTION OF SMALL QUANTITIES OF CALCIUM Adding 5 mgrms. of calcium. Added salts. Result. No added salt. Immediate pptn. Sodium chloride, 1 grm. Borax, 1 grm. Sodium potassium tartrate, 1 grm.Potassium citrate, 1 grm. Variations in the concentration of the reagents did not appreciably improve matters. It was found that even 0.25 grm. of potassium citrate in 60 C.C. of solution prevented the precipitation of 2 mgrms. of calcium. Further complications would be introduced if magnesium were also present in the salt as an impurity. CALCIUM OLEATE TEsT.-The formation of an opalescence on the addition of sodium oleate solution to a solution is an extremely delicate test for calcium. Under the best conditions 0.01 mgrm. of calcium in 50 C.C. of solution, or 0.00002 per cent., can just be detected. The test is also, of course, a test for magnesium, but is much less sensitive, 0-6 mgrm. in 50 C.C. of solution, or 0-0012 per cent., being the minimum quantity which can be detected.Further, within certain limits of concentration the pre- cipitation of magnesium is entirely suppressed in the presence of potassium citrate, whilst the sensitiveness of the calcium test is actually increased. The best conditions for the detection of calcium were found to be as follows: Take 50 C.C. of the solution containing calcium, which should be neutral or slightly alkaline. Dissolve in it 2 grms. of potassium citrate, and add 0-3 C.C. of a solution prepared by dissolving 10 grms. of oleic acid in 200 C.C. of 1 per cent. sodium hydroxide. A certain excess of alkali is desirable for the best results. The test is only satisfactory between certain limits of calcium concentration. With quantities exceeding 1 mgrm.in 60 C.C. the opalescence is actually reduced. Under the above conditions quantities of mag- nesium up to 15 mgrms. give no opalescence. Summarising the results, the oleate test is excellent for quantities of calcium varying from 0-01 mgrm. up to 1 mgrm. in the absence of more than 10 mgrms. of magnesium, and within these limits in the absence of other salts the opalescence appears proportional to the calcium present. Further experiments showed, however, that, in spite of its delicacy, the oleate test is not suitable for the purpose in view. Possibly, if the test could be carried out, using standards containing the same concentration of the same salt, it would be satisfactory, but this is hardly practicable. The addition of other salts, even in the absence of potassium citrate, caused the results to be erratic. This was partly due to their “salting out ” effect on the soap, which sometimes caused flocculation, but this was not the whole explanation. Almost immediate pptn. Slight ppt. after 30 minutes. Slight ppt. after 30 minutes. No ppt. This line of investigation was therefore abandoned. Mix and allow the mixture to stand. An excess of the reagent gives less opalescence.

ISSN:0003-2654    

DOI:10.1039/AN9325700655

出版商:RSC    

年代:1932

数据来源: RSC