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/AN9325700137

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

138 CLARKE AND BRADSHAW THE CALCIUM FLUORIDE METHOD The Calcium Fluoride Method for the Deter-mination of Fluoride with Special Reference to the Analysis of Nickel-Plating Solutions* BY S. G. CLARKE PH.D. A.I.C. AND W. N. BRADSHAW B.Sc. ONE type of modern nickel-plating solution contains a high concentration of nickel sulphate together with additions of potassium or sodium chloride to maintain anode efficiency and of potassium or sodium fluoride and boric acid to act as buffering agents. The solution may also contain small quantities of iron etc. as impurities. No difficulties arise in the determination of the nickel sulphate etc., and the problem of the determination of the borate in this type of solution has recently been satisfactorily solved by Willard and Ashworth (Amer.EZectro$Zaters’ SOC. Monthly Review August 1929 p. 7). A process for the determination of the fluoride has been published (Hammond J . Ind. Eng. Chem. 1924 16 938) in which the lead chlorofluoride precipitation method is employed; the method is not easy to carry out and has in our hands given a distinctly incomplete recovery of the fluoride. In a search for a suitable method we investigated the possibilities of the calcium fluoride precipitation method and we have found how this can be used to provide a reasonably rapid and accurate method for the determination of the fluoride in these nickel-plating solutions. Our work further shows how in the absence of interfering substances the traditional calcium fluoride process can be simplified and rendered more rapid and accurate.The calcium fluoride method continues to occupy a prominent position in textbooks since it has fewer disadvantages than other methods for the determination of fluoride. In a modification of this method by Rose (Autn. 1849,72 343) some calcium carbonate is made to precipitate with the calcium fluoride with the object of rendering the precipitate less difficult to filter. It is clear that this procedure restricts the method to solutions from which heavy metals e.g. nickel have been * Communication from the Research Department Woolwich FOR THE DETERMINATION OF FLUORIDE 139 removed. Moreover the addition of sodium carbonate which is recommended for producing the precipitate of calcium carbonate may reduce the concentration of the calcium ions in the solution at the time of precipitation to a very low value, perhaps beneath that required for reducing the solubility of the calcium fluoride to the minimum.We have found that calcium fluoride can be precipitated and filtered practically quantitatively with ease even in the absence of calcium carbonate or other co-precipitant thus avoiding the subsequent troublesome and often incomplete removal of this from the precipitate. This ease of precipitation and filtration can be achieved by paying attention to the conditions under which the calcium fluoride is precipitated and also to the method of filtering. The method which we advocate provides for an excess of calcium chloride for reducing the solubility of the calcium fluoride. For filtering off the precipitate we suggest the use of a paper-pulp filter* as absolutely essential not only because this retains the precipitate of calcium fluoride more effectively than a folded filter paper but also so that the washing process may be carried out with the minimum of washing liquid.It is probably from a lack of attention to these points that the calcium fluoride method has acquired a reputation for a tendency to give unsatisfactory results. The statement made in the recent textbook of Hillebrand and Lundell (A+$Zied Inorganic Analysis 1929) that ammonium chloride in the solution “ holds up” the precipitate of calcium fluoride has not been confirmed. We have obtained at least as good results from precipitation in presence of ammonium chloride as in its absence. Indeed the presence of ammonium chloride is essential in applying the calcium fluoride method to solutions containing sulphate e.g.nickel-piating solutions because by virtue of the greatly increased solubility of calcium sulphate in ammonium chloride solution the precipitation of calcium sulphate may be substantially prevented. mental work on the following lines was undertaken to find the best conditions for precipitating fluoride as calcium fluoride and it is shown that the precipitation can be successfully carried out from solutions having a wide range of fiH values, containing fluoride either alone or with nickel chloride boric acid and considerable quantities of ammonium chloride. The Standard Fhoride.-Some difficulty was at first experienced in obtaining a pure fluoride on which to base the work.Commercial “pure” sodium fluoride is liable to contain among other substances sodium fluosilicate the solubility of which is very near that of sodium fluoride; the salt is extremely difficult to re-crystallise because both the solubility and the solubility gradient with temperature are low; in any case its satisfactory recrystallisation demands large platinum vessels. Potassium fluoride being a hydrated salt and somewhat hygroscopic, was considered unsuitable. A possibility which had to be abandoned was that of using diluted “ A.R.” hydrofluoric acid standardised by titration; this acid on analysis was found to contain about 1 per cent. of silicon as hydrofluosilicic acid, which since it behaves on titration with alkali in the cold as a dibasic acid vitiates PRECIPITATION OF CALCIUM FLUORIDE I N ABSENCE OF SuLPHATEs.-Experi-* The preparation of these filters from “ashless” filter paper macerated with water is described in e.g.the following books Picard Steel Analysis 1914 p. 6 ; Hackney Quantitatior inorganic Analysis 1930 p. 15 140 CLARKE AND BRADSHAW THE CALCIUM FLUORIDE METHOD the calculation of the total fluorine as hydrogen fluoride. Mre adopted as a standard material sodium fluoride prepared as follows : A fairly strong solution of potassium fluoride was prepared in a platinum dish and filtered through a gutta-percha funnel the filtrate being allowed to drop slowly into a well-shaken equimolecular roughly half-saturated solution of sodium chloride contained in a pyrex flask. The finely crystalline sodium fluoride which rapidly separated out was filtered off without delay washed with water and dried at 100" C.Its weight remained unchanged at 500" C. showing that it was anhydrous. Tests showed that it was practically free from chlorides. Precipitation of Calcium Fluoride from Neutral Solution.-Solutions having the volumes shown in Table I were made up to contain various amounts of sodium fluoride. These solutions were rendered slightly acid with hydrochloric acid; a few drops of methyl red indicator (0.02 per cent. in 50 per cent. alcohol) and 10 C.C. of calcium chloride solution (10 per cent. CaCl,) were added followed by dilute ammonia until the indicator just changed to yellow. The liquids were boiled for about one minute cooled in running water for fifteen minutes and filtered through small compressed pulp filters.The precipitates were washed four times with cold ammonium nitrate solution (5 per cent.) and twice with cold water; about 10 C.C. of liquid was used for each washing. The filters were heated in weighed platinum capsules at a moderate temperature (400 to 600°C.) until all the carbonaceous matter had burned off and then a t about 800" C. for 10 minutes. In some cases the residue of calcium fluoride was converted to calcium sulphate. The results are shown in Table I. Fluorine added. Grm. Nil-Blank 0*0100 0.0200 0.0400 Nil-Blank 0~0100 0.0200 0.0400 Volume of solution before pre-cipitation. 50 50 50 50 100 100 100 100 C.C. TABLE Weight of residue Grm.[O*OOOS] 0.0216-0.0008 0*0424-0*0008 0.0837-0*0008 0-0201-0.0011 0~0407-0*0011 0*0815-0*0011 (CaF2) ' [0~0011] I Fluorine found. Grm. 0*0101 0.0202 0.0404 0.0092 0.0193 0.0391 Weight of residue (CaSO,) . Grm. [O*OO 1 81 0*0375-0*00 18 O.074P0.00 18 [0*0023] 0.07 12-0.0023 0*1468-0*00 18 0*0349-0.0023 0*1430-0*0023 Equiva-lent to fluorine. Grm. 0.0009 0.0202 0.0404 0.0093 0.0192 0.0392 The high " blank " obtained in this series of experiments was most probably caused by carbon dioxide being present in the water and by ammonia being used and gaining access to the solution during the boiling etc. By using a washing liquid containing 1 per cent. of acetic acid and 5 per cent. of ammonium nitrate, the "blank" was reduced to about 0.0003 grm.as shown in Table 11. This washing liquid was adopted throughout the subsequent work. Volume of solution Fluorine before pre-added. cipitation. Grm. C.C. Nil-Blank 50 0-0100 50 0.0200 50 0-0400 50 Weight of residue Fluorine (CaF2). found. Grm . Grm . 0-0200-0~0003 0.0096 0.0408-0*0003 0.0197 0.08 15-0-0003 0.0395 [0*0003] Weight of Equiva-residue lent to (CaSO,). fluorine. Grm. Grm. [0*0005] 0*0344-0*0005 0.0095 0*0713-0*0005 0.0197 0*1431-0.0005 0.039 FOR THE DETERMINATION OF FLUORIDE 141 Precipitation of Calcium Fluoride from Acid Solution.-Table I11 shows the results obtained in the precipitation of calcium fluoride from solutions con-taining various concentrations of acetic acid.The solutions (50 c.c.) containing sodium fluoride were made just alkaline to brom-phenol blue and acetic acid was added to give the concentrations shown; the method of precipitation etc. already outlined was followed. Fluorine added. Grm. Nil-Blank 0.0100 0~0200 0.0400 0~0100 0~0100 0.0398 0.0398 0.0398 Nil-Blank Acetic acid. Per Cent. 1 1 1 1 10 25 10 25 50 25 TABLE I11 Weight of residue Fluorine (CaF.2) * found. Grm. Grm. 0.01 98-0.0002 0.0095 0*0408-0.0002 0.0197 0.08 10-0~0002 0.0394 0.01 9&0-0002 0.0094 0.01 98-0.0002 0.0095 0.08 10-0*0002 0.0393 0.08 10-0-0002 0.0393 0*0810-0~0002 0.0393 [0-000z] [O. 00021 Weight of Equiva-residue lent to (CaSO,). fluorine. Grm. Grm.[0*0003] 0.0339-0.0003 0.0094 0.07 11-0*0003 0.0197 0.1409-0.0003 0.0392 Precipitation of CalciHm Fluoride from Solutions containing Boric Acid Nickel Chloride and Ammonium Chloride.-The results recorded in Table IV were obtained. In each experiment the fluoride was precipitated by the addition of 10 C.C. of calcium chloride solution (10 per cent. of CaCb) the fluoride solution containing 1 per cent. of acetic acid. TABLE IV Added. Found. A f A \ I I Equivalent Fluorine. CaF,. Fluorine. CaSO,. to fluorine. Gl-lll. Grm. Grm. Grm. Grm. Grm. 0-0200 0.02 HsBOs 0-0397 0-0193 0.0200 0.20 0.0397 0.0193 0.0200 0.5 NH4Cl 0.0402 0.0196 0-0200 5-0 0.0423 0.0206 0~0200 0.20 Hs’BOs; 5NH,Cl 0.0406 0.0198 0.0700 0.0196 0.0400 0.02 HsBOS 0.0794 0.0387 0-0400 0.20 0.0810 0-0394 0.0400 0.20 HsBOs; 5NH4C1 0.0821 0.0400 0.1429 0.0399 0.0400 2.0 NiC4.6H20 0.0822 0.0400 0.1422 0.0397 0.0400 2.0 NiC&.6H20; 5NH4C1 0.0840 0.0409 0*0400 2.0 NiC4.6H20 0.0825 0.0402 0.0400 2.0 NiC12.6H,0; 5NH,CI 0-0827 0.0402 In the last two experiments precipitation took place from 10 per cent.acetic acid solution instead of from 1 per cent. solution. THE INTERFERENCE OF IRON AND ITS AVOIDANCE.-h planning a process for the determination of fluoride in nickel-plating solutions attention had to be given to the interference of (ferric) iron. In proportion to the amount of ferric salts present the precipitation of calcium fluoride is either partly or completely pre-vented. Attempts to overcome this interference by the addition of organic hydroxy-compounds e.g.mannitol lactic acid. citric acid etc. were unsuccessful. It was found however that quantitative precipitation of the fluoride could be effected if the iron in the solution was reduced to the ferrous condition the followin 142 CLARKE AND BRADSHAW THE CALCIUM FLUORIDE METHOD method being adopted:-To the solution containing 10 per cent. of acetic acid, were added 10 C.C. of calcium chloride solution (10 per cent.) and 1 C.C. of hydrazine hydrochloride solution (20 per cent.). The solution was heated to boiling. The brown colour of the ferric acetate (which is not precipitated) rapidly became bleached and the calcium fluoride then precipitated. After boiling for about half a minute the solution was cooled in running water for 15 minutes and the filtration etc.of the calcium fluoride carried out as usual. Table V contains the results obtained, TABLE V. Added. Found. A 7 -1 Iron Nickel Boric Ammonium Calcium Fluorine. (as FeCl,). (as NiCl,) . acid. chloride. fluoride. Fluorine. Grm. Grm. Grm. Grm. Grm. Grm. Grm. 0*0400 0.10 - - 5-0 0.08 11 0.0395 0.0400 0.05 0.5 0.20 5.0 0.081 1 0.0395 0-0400 0.05 0.5 0.20 5.0 0.0821 0.0400 When the amount of iron is small it can be removed from the solution by precipitation as ferric hydroxide without causing any loss of fluoride. This method would appear to be more convenient than the above in the determination of fluoride in nickel-plating solutions and will be referred to later in that connection. PRECIPITATION OF CALCIUM FLUORIDE FROM SOLUTIONS CONTAINING SULPHATE.-The low solubility of cdcium sulphate in water renders it practically impossible to precipitate calcium fluoride quantitatively in a pure condition by the addition of calcium chloride to a solution containing fluoride and sulphate.This is especially true of a nickel-plating solution because the ratio of sulphate to fluoride is large. We have found also that there is a noticeable tendency for calcium sulphate to be adsorbed by a precipitate of calcium fluoride when this is formed in a solution only partly saturated with calcium sulphate. We have, however been able to take advantage of the enhanced solubility of calcium sulphate in ammonium chloride solution to work out a feasible process for precipitating calcium fluoride from a solution containing much sulphate.By employing a regulated excess of calcium chloride only a small quantity of calcium sulphate is precipitated with the calcium fluoride; a correction can be made for this by deducting from the weight of the precipitate the weight of the calcium sulphate, calculated from a determination of sulphate in it. The best results were obtained by precipitating the calcium fluoride from a neutral or slightly ammoniacal solution; good results in the presence of sulphate were not obtained when solutions containing acetic acid were used. Details of the method adopted are incorporated in the following process proposed for the determination of fluoride in nickel-plating solutions. DETERMINATION OF FLUORIDE IN FLUORIDE-BORATE NICKEL-PLATING SOLUTIoNS.-Ten C.C.of the solution are diluted to 25 c.c. and 5 C.C. of ammonia" (sp. gr. 0.88) are added. The liquid is boiled for about half a minute and filtered through a small filter paper (e.g. Whatman 7 cm. No. 41). The beaker is rinsed out four times with 5 C.C. of 5 per cent. ammonia on to the filter which is allowed thoroughly to drain each time. The precipitate if any of ferric hydroxide is * This will provide the necessary amount of ammonium chloride FOR THE DETERMINATION OF FLUORIDE 143 rejected and the filtrate having a volume of about 45 c.c. is made slightly acid with concentrated hydrochloric acid and 2.5 C.C. of calcium chloride solution (10 per cent. made from anhydrous salt) are added slowly drop by drop (this quantity suffices for the amount of fluoride normally to be found in these nickel-plating solutions i.e.up to about 10 grms. of sodium fluoride per litre; see note below); the solution is then made just alkaline with ammonia boiled for about half a minute and cooled in running water for fifteen minutes. The precipitate of calcium fluoride (with adsorbed calcium sulphate) is filtered off on a small well-compressed pulp filter and washed four times with 5 per cent. ammonium nitrate solution containing 1 per cent. of acetic acid and then twice with cold water. The total amount of washing liquid used should not exceed 50 C.C. The filter, with the precipitate is transferred to a platinum capsule heated at about 400-500°C. until the carbonaceous matter has been destroyed and then ignited at -700-800" C. for ten minutes.After weighing 5 C.C. of concentrated hydrochloric acid (free from sulphate) are added to the residue in the dish which is then heated until all the acid has evaporated. This treatment is repeated until the residue has been completely attacked and a clear solution can be obtained in the 5 C.C. of acid. The 5 C.C. of solution are transferred to a conical flask diluted to about 100 c.c., and heated to boiling and 20 C.C. of barium chloride (10 per cent.) solution are added slowly. The barium sulphate is allowed to settle and is then filtered off, washed ignited and weighed. The equivalent weight of calcium sulphate is deducted from the weight of the original precipitate and the weight of calcium fluoride is thus obtained. TABLE VI Added. Found. A A r \ r G m .1 0~0100 2 0.0200 3 0.0400 4 0.0800 5 *0*0216 6 *0*0288 7 *0.0592 Grm. Grm. Grm. C.C. 2.4 0.2 0.01 2.5 2.4 0-2 0.01 2-5 2.4 0.2 0.01 2.5 2.4 0 2 0.01 3.5 2.4 0.2 - 2.5 2.4 0.2 - 2.5 2.4 0.2 - 2.5 Grm. 0.0195 0-0419 0.0891 0.1750 0.0454 0.0622 0.1298 G m . 0.0045 0.0080 0.0175 0.0300 0.0095 0.0138 0*0300 Grm. 0.0026 0-0046 0.0101 0-0 174 0.0055 0.0080 0.0174 GXIl. 0.0167 0.0373 0.0790 0.1576 0.0399 0.0542 0.1124 GXIl. 0.008 1 0*0182 0.0385 0.0768 0.0194 0.0264 0.0547 Grm. 0.0101 0.0202 0,0405 0.0788 0.0214 0.0284 0.0567t * Amount of fluoride added to test solutions unknown to the analyst. t Low result indicates that insufficiency of calcium chloride was added.Table VI shows results which were obtained with solutions made up to simu-late nickel-plating solutions containing 240 grms. of nickel sulphate and 20 grms. of boric acid per litre with different amounts of sodium fluoride added; to some of the solutions iron was added in greater amount however than would be expected in a nickel-plating solution in order to verify its non-interference in the process. It will be noticed that the results are lower than the theoretical by a fairly constant amount viz. 0.002 grm.; this seems due to a solubility effect probably introduced by the high nickel and sulphate concentration of the solution and it is therefore, suggested that a correction of this order should be applied to the results obtained 144 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE IN CRIMINAL TRIALS The addition of 2.5 C.C. of calcium chloride solution (10 per cent.) is satis-factory for the precipitation (in a volume of 50 c.c.) of fluorine from 10 C.C. of nickel-plating solution containing not more than 10 grms. of sodium fluoride per litre which is a concentration not usually exceeded in practice. In the event of the solution containing a higher concentration of sodium fluoride it would be necessary to increase the amount of calcium chloride for the precipitation; in Experiment 4 (in the table) in which 0.08 grm. of fluorine was present in 10 C.C. (corresponding with 17.7 grms. of sodium fluoride per litre) 3-5 C.C. of calcium chloride were used. It is recommended however that this process should be carried out as described and if the result comes out at more than 10 grms. of sodium fluoride per litre the determination should be repeated using slightly more calcium chloride for the precipitation. The amount of calcium chloride for the precipitation must be controlled with reasonable care to keep the correction for calcium sulphate in the final precipitate as low as possible yet (at the same time) to give a sufficient excess of calcium ions in the solution for the fluoride precipitation

ISSN:0003-2654    

DOI:10.1039/AN9325700138

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

144 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE IN CRIMINAL TRIALS Scientific Documentary Evidence in Criminal Trials BY C. AINSWORTH MITCHELL D.Sc. F.I.C. (Read at the SzGmmer Meeting North of England Section July 4 1931) WHEN your Honorary Secretary (Mr. J. Stubbs) asked me to read a paper at your Summer Meeting and this request was repeated by our President I felt that it would be ungracious not to respond and I therefore agreed to give a survey of the scientific evidence which may be based on documents in criminal trials and to illustrate this by cases within my own experience. Scientific documentary evidence is of course circumstantial in character, and it is a common practice for counsel for the defence in criminal trials to decry all circumstantial evidence notwithstanding the fact that it is often more trust-worthy than personal testimony.Apart from that if it were excluded there would be few convictions even of dishonest tradesmen and fewer still of the inveterate poisoner who is the last person to advertise his intentions or to let his acts be seen. The rules that govern documentary evidence are the same as those governing any other expert evidence. For example since the leading case of Seaman v. NethercLft (1876) a witness on oath is in a privileged position whether he asserts that a sample has been grossly adulterated or that a signature is a forgery. There are also certain judicial decisions which have been given in connection with documents and are also applicable to scientific evidence in general. For instance Mr.Justice Finlay in the case of Rex v. Henry (1929) allowed a tracing to be shown to the jury and in the case of Rex v. Podmore (1930) the Lord Chief Justice held that a photograph upon which marks had been made with the objec MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE IN CRIMINAL TRIALS 145 of directing the attention of the jury to certain details in the original document, was admissible since it went to strengthen the evidence. Many of the scientific data upon which evidence as applied to documents can be based have been accumulated comparatively recently and new cases frequently present problems for which no solution can be found in textbooks. These may best be considered under the headings of the various materials, beginning with ink. EVIDENCE RELATING TO INKS.-Di$erentiation of Writing Inks.-The first occasion on which evidence as to differences in ordinary blue-black writing inks on a document was given in this country was at the trial of Brinkley in 1907 (Rex v.Bvinkley). In that case a forged will was the motive for an unintentional murder (if that is not a contradiction in terms) for the prisoner had tried to poison a man whose name appeared as a witness on the will but who had stated that he had signed only what he had been told was a petition for an outing. A bottle of stout dosed with prussic acid was left in this man’s lodgings where it was drunk by his landlord and landlady both of whom died. An important point in the evidence was whether the statement about the signing of a petition for an outing in a public-house was true and accordingly the ink used in that public-house was compared with the ink in the signature upon the will.Chemical tests could not be made since the President of the Probate Court refused his permission for the will to be touched but fortunately an optical examination was sufficient for the purpose. The ink (“ Azuryte ”) from the public-house contained a particularly brilliant blue dye which enabled it to be distinguished readily from most other inks in common use at that time; and by first matching the inks on the will under the microscope and then preparing broad colour bands which could be compared by means of a tintometer it was possible to demonstrate in Court that the ink from the public-house agreed exactly with the ink in the signature on the alleged will and also that there were three separate inks upon that document.Brinkley admitted this but tried to explain it away by saying that he had given two bottles of ink to a little girl. He was convicted and executed. Prior to the war English ink manufacturers were using a large variety of blue dyes as provisional colouring matters and this was helpful for distinguishing between different inks whether by optical or chemical methods (see ANALYST, 1908 33 SO) but for some years past the Board of Trade has consistently refused to allow any dyestuffs to be imported for ink-making with the result that the provisional colouring matter in writing ink is usually the same “ Ink Blue ” (Soluble Blue) and chemical tests must now be based in the main on the different pro-portions of dye tannin substances and iron in the inks.Osborn’s comparison microscope which has been devised since the Brinkley case is a valuable instrument for comparing colours and recording their Lovibond values although it is not advisable to attempt to demonstrate its use to a jury; the colour-strip method as used in that trial is still the simplest way of showing in Court differences of colour in inks on a document. Gradation of CoZozcr.-The colour of an ink will naturally vary with such con-ditions as the length of time the ink has remained exposed to the air in an inkpot, or the time it was left upon paper before blotting. These points are of considerabl 146 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS importance in judging whether the whole of a given piece of writing was done at the same time as may readily be seen on comparing successive entries in hotel registers.I t was a significant fact that in the case of Bishop of Lincoln v. Wakeford (1921) the disputed words “and wife” in the two entries in the hotel book agreed exactly in gradation of tone with the preceding words “J. Wakeford.” I t would have been an exceptionally skilful forger who could have twice completed those entries in ink of exactly the correct shade. Photographic Di$erentiation.-Another optical method of distinguishing between two writing inks one of which is richer in blue units than the other is by means of photography on an ordinary “process” plate. When such difference in colour is present two inks which when examined under the microscope appear to match one another may show a pronounced difference when photographed the ink richer in red appearing much darker in the print than in the original document.This method afforded conclusive evidence in the case of Rex v. Cornwallis (1919), in which a woman produced a letter acknowledging the receipt of l200 with a final “0” added to the amount in a different ink. A remarkable case in which a photographic reproduction suggested forgery was that of Hawes v. Skelton (1924) in which a will was discovered in the pocket of the overall of a woman who was bathing a dog. The signature on this will showed different colours and had manifestly been re-touched but the Judge (Mr. Justice Horridge) was not satisfied that these abnormalities were sufficient to condemn the document and deferred the case for a scientific opinion.The bottle of ink with which the document was alleged to have been signed was pro-duced in Court. It was said to contain a mixture of three different inks bought at a sale and experiments showed that this mixture was capable of accounting for all the abnormalities found on the document. It produced writing of different colours according to the depth to which the pen was dipped into the ink and the ink ran badly from the nib necessitating re-touching of the writing. As a result of this evidence the Judge pronounced in favour of the will. AGE OF INK IN WRITING.-The change of colour which rapidly takes place when ink begins to oxidise on paper may sometimes afford proof that writing is recent.Thus in a claim brought against an insurance company by a clothier for the alleged loss of his stock by fire it was found that entries in a stock book, which purported to be two years old darkened perceptibly in the course of three or four days and must therefore have been comparatively recent. The colour readings in tintometer units were taken on successive days during the period of the test and were checked by another observer so that there was no doubt as to the progressive change in colour. But at best evidence of this kind is unsatisfactory since it is subjective in character and cannot be supported by photographic proof or checked by subsequent examination. Chemical evidence of the age of ink is much more convincing than colour records since the test can be repeatedly checked as I have shown in my discussion on the subject (ANALYST 1920 40 247).In the case of Rex v. Pilcher (1911) special permission was obtained from the President of the Probate Court for chemical tests to be applied to the inks upon a will purporting to be thirteen years old. All the inks on the document readily ran over the paper when treated wit MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE IN CRIMINAL TRIALS 147 reagents and formed blue smudges whereas the inks on the older counterfoils of cheque books of the deceased woman which dated back for six or eight years, remained practically unaffected by the reagents under the same conditions; hence the inks on the disputed will could not have been as old as its date. After this evidence had been given Colonel Pilcher confessed that he had uttered the will, knowing it to be a forgery and he was sentenced to three years’ imprisonment.ANACHRONISMS IN INKS.-on several occasions fraudulent claims for old-age pensions have been exposed owing to the fact that the entries in family Bibles, produced as evidence of age were written in blue-black ink containing an aniline dye whereas aniline dyes had not been discovered at the dates mentioned. Such dyes appear to have been introduced into writing fluids in this country about 1880, but the earliest instance I have yet found in old ledgers was an entry written in 1885. A more uncommon anachronism was disclosed in connection with two docu-ments in the case of Rex v. Rogers (1930). It would need the pen of a Thomas Hardy to do justice to the story unfolded at that trial of a man who had foisted forged documents on to an ignorant old woman an old-age pensioner and had received E5 from her.She was a descendant of William Penn the Quaker and claimed to be entitled to his estates. The two documents which she was led to believe would establish her claim were genuine old parchments one of which related to a conveyance of land by the Earl and Countess of Yarmouth in 1688. In each instance the name of “ William Penn” appeared after the signatures of the other witnesses and was apparently in the same kind of iron-gall ink which had disintegrated with age leaving a residue of oxidised iron compounds. But the inks of the William Penn signatures unlike all other writing on the documents, contained no iron and when treated with a minute drop of hydrochloric acid, became milky.This was found to be due to silver which had become brown -in other words the ink had the characteristics of a silver marking ink. This discovery became still more significant when counsel for the defence asked whether the forgery could have been perpetrated by William Ireland who was responsible for the wholesale forgery of Shakespearian documents at the close of the eighteenth century. Ireland afterwards wrote a full confession of his methods, and from the description of his ink he was evidently using a preparation con-taining a silver salt.* The answers to the question raised about Ireland were (1) Ireland did not use a steel pen for his forgeries as had manifestly been used in the Penn forgeries * The Confessions of William Henry Ireland containing the Particulars of his Fabrication of the Shakspeare Manuscripts (1805) p.39. “One of the journeymen looking at the manuscript, informed me that he could give me a mixture that would resemble old ink much more than that which I had used; and in consequence of my request he immediately mixed together in a phial three different liquids used by bookbinders in marbling the covers of their calf bindings. These ingredients being shaken up produced a fermentation; when the froth having subsided the liquid was of a dark brown colour. The young man then wrote his name with this mixture but i t was very faint on the paper; however on holding it for a few seconds before the fire the ink gradually assumed a very dark brown appearance.. . . It was with the same ink I afterwards wrote the Shaksperian manuscripts. Their scorched appearance originated in my being compelled to hold them to the fire as before stated; and as I was constantly fearful of interruption I some-times placed them so near the bars as to injure the paper; which was done in order to complete and conceal them as speedily as possible from any unexpected person who might come suddenly into the chambers.” (Cf. Plate Fig. 4. 148 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS (Fig. 1); steel pens were not invented until 1808. (2) Ireland confined his atten-tions to fifteenth and sixteenth century documents; in those days there would have been no motive €or producing autographs of William Penn.(3) There were no characteristics in the writing to suggest that Ireland had had anything to do with the forgery which was a clumsy imitation of the genuine writing as may be seen by comparison with the signature on one of the genuine Penn documents brought into Court for comparison (see Plate Figs. 2 and 3). The prisoner was found guilty of uttering the forged documents and was sentenced to a term of imprisonment. Fig. 1. Enlargement of forged signature of William Penn-showing the effect of a steel nib. INK IN CREASES IN PAPER.-The way in which a paper has been folded may be significant especially when there is writing across the fold. If the writing has been added since the folding of the paper it will sometimes be found that the ink has spread slightly along the crease owing to the paper having become more porous through a break in the surface sizing after repeated folding in the same place.In a case tried in 1929 a fact of this kind afforded proof that some writing on an agreement was not so old as the document itself. SEQUENCE OF STROKES IS WRITING.-The conditions under which it is possible to be certain that a stroke in writing which appears to be on the top of another stroke really is uppermost have been discussed in a previous paper (Mitchell and Ward ANALYST 1927 52 580). Briefly the rule is that if one of the pigments in the intersecting lines is a thin film of colour as in stamping ink or blue-black writing ink which has been blotted immediately after writing it is not possible to express an opinion which line was made first; but if the pigment is sufficiently dense as in printing ink or if a layer of solid pigment forms as when iron-gall inks oxidise on paper definite conclusions may be drawn.These conditions were present in the case of Rex v. Cohen discussed in a former paper (ANALYST 1920, 45 252). In another case (L0nnel.t v. Lonnen) a codicil to a will which two wit-nesses swore that they had seen signed was upset by the fact that at two points the writing of the codicil intersected the writing of the signature of the testator DOCUMENTS PRODUCED OR CITED IN THE CASE OF REX v. ROGERS 2 3 4 2. 3. 4. Forged signature of William Penn. Genuine signature and seal of William Penn when Governor of Pennsylvania, July 31st 1684 (Penn MSS Library Society of Friends).One of Ireland’s forgeries of Shakespeare’s writing and signature on the fly-leaf of a book “ The Catholikes’ Supplication,” 1603 (Brit. Museum Stowe 996, 576 a. 34). The darkening of the paper was due to scorching (luring thc heating of the silver ink (cf. p. 147) MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS 149 and could be demonstrated by means of enlarged photography to be uppermost, thereby proving that the codicil had been inserted after the will had been signed. With black lead pencil writing the sequence of strokes can always be deter-mined by the lines of the silver striations (due to the impurities in the graphite or to the added clay) which are seen when the strokes are examined in oblique lighting (see ANALYST 1922 47 379).DIFFERENTIATION OF PENCIL PIGMENTs-In some cases microscopical differentiation of pencil marks is possible ( J . SOC. Chem. Ind. 1919 38 3 8 1 ~ ) ~ but great caution is necessary since it is possible by wetting the lead or varying the pressure to alter the way in which pigment is deposited on the paper and the series of strokes containing approximately the same amounts of pigment must be chosen for the comparison. The differentiation of old graphite pencils from modern composite pencils is usually practicable however owing to the fact that the silver striations of the former are irregular and interrupted whilst those of the latter are like strings of beads. Chemical tests depend upon the fact that graphites contain widely differing amounts of iron and chlorides and in exceptional cases there is sufficient titanium to respond to a micro-chemical test.Coloured pencils can usually be distinguished from one another without much difficulty (see ANALYST 1922 47 385). COPYING INK PENCILS.-An outline of the methods of distinguishing between the pigments of copying ink pencils on paper will be found in THE ANALYST (1917, 42 3). There is more scope than with ordinary blacklead pencils owing to the fact that there are usually three constituents present-kaolin clay violet dyestuff, and blacklead and that the proportions of these affect the reactions given by the writing. In the case of Rex v. Wood (1907) in which charred fragments of paper were found in the grate of the house where a woman had been murdered it was possible to prove by a series of tests that the pigment on the paper agreed with that of a copying ink pencil in the possession of an artist who was accused of the murder.Ultimately he admitted having written the letter but was acquitted of the murder. The possibility of such pigments resisting the action of sea-water for some weeks was raised in the case of Macbetlz v. King (1916) in which the genuineness of a stave of wood with a message supposed to have originated from a steamship, presumably sunk by a torpedo was a point at issue. Experiments described to the Court showed that copying ink pencil writing on a piece of oak would not be obliterated by six weeks’ exposure to sea-water and air. The behaviour of copying ink pencil writing towards various solvents had to be determined in the case of Rex v.Podmore (1930) in which a scrap of paper about two inches square which was found behind a barrel in a garage at Southampton where a man had been murdered led ultimately to the conviction of the murderer. This fragment was caked with dirt and soaked in oil and had been repeatedly trodden under foot and the problem was to remove the dirt and oil without also removing the pigment of the copying ink pencil. After numerous experiments with various makes of copying ink pencil petroleum spirit was found to be suitable for the purpose and a message from a man calling himself “ W. F. Thomas ” wa 150 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS left upon the paper. Until then it was not known that anyone of the name of “Thomas” (an alias of Podmore) had been in any way connected with the victim.The use of ultra-violet light made it possible to read much more of this message than could be brought out by an ordinary photograph but to avoid any suggestion of the use of the imagination the evidence on this fragment at the trial was restricted to the words and characters which the jury could see for themselves. INDENTATIONS IN PAPER.-Another document produced at this trial was a leaf from a note-book showing indentations which had presumably been made by the pressure of a pencil on another leaf of the book subsequently torn out. By means of photography with the use of oblique lighting to illuminate the edges of the indentations words relating to bogus orders with the initials of “ Thomas,” were rendered visible and this formed a further link in the evidence which led to the conviction of Podmore.SECRET WRITING.-The search for secret writing in a document is usually only needed on special occasions such as the detection of espionage in war time or irregular communication with the outside world by prisoners. The substances which are capable of being used as invisible inks are almost innumerable but, broadly speaking they fall into two classes-those forming a coloured compound on treatment with a mordant and those which become visible when examined by special optical methods such as ultra-violet light. A discussion of the subject will be found in my book The Scienti$c Examination of Documeutts p. 153 (Chas.Griffin & Co.) and in Lucas’s Forensic Chemistry 2nd Ed. p. 105 (E. Arnold & Co.). In the earlier trials of German spies during the war (Rex v. Kuepferle (Times Report May 15 1915) Rex v. Miiller an.d Hahn and some others) the primitive method of writing with lemon juice was employed and evidence was required to prove that steel pens in the possession of the accused had deposits upon them consistent with their having been dipped into lemon juice whilst cut lemons gave reactions for iron at points where apparently something had been inserted into them. In later trials more elaborate methods of secret writing were employed as may be gathered from the story of these spy cases in Felstead’s German S+ies at Bay (Hutchinson). The knowledge of the use of saliva for secret writing and of its development with a dilute solution of ink was common property long before the war (cj.Dennstedt and Voigtlander Lehrbuch der gerichtlichert Chemie 1907 p. 122). In a study of the action of saliva upon iron-gall ink (ANALYST 1920 45 256) I have shown that it behaves like an oxydase accelerating the oxidation of the ferrous tannate and forming a compound which is distinct from that which forms normally when ink is oxidised by exposure to the air. The process of the development with ink of writing done with saliva thus appears to be partly physical (absorption of dye where the fibre of the paper has been indented) and partly chemical (accelerated oxidation of the ink). TYPEWRITING.-Fortunately it is not generally realised especially by those who are given to writing anonymous letters that typewriting can be identified with that produced by a particular machine with a much greater degree of certainty than the identification of handwriting.Apart from the fact that eac MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS 151 manufacturer uses a different fount of type which is usually varied in successive models every machine has its individual faults of alignment and displaced and imperfect letters by means of which its identity and in certain cases its age, can be established. The best methods and instruments for recognising and demonstrating such identity are described by Osborn in his Questioned Documents (2nd Ed. p. 437, et seq.). Identity in the relative positions of various letters is shown by means of photographs taken under glasses ruled in standard squares and the typing produced by battered letters is easily recognised even by an unintelligent jury, when shown in an enlarged photograph.Osborn cites many examples of cases in which the evidence derived from a study of typewritten documents has been incontrovertible and these might be supplemented by numerous cases in this country. Among the most recent of these is Rex v. Parry (1930) in which a former tax collector was convicted of inducing an old man and his wife to make a successful fraudulent claim for the repayment of income tax by which he also benefited. He denied that the fraudulent returns had originated from his office, but the typing upon them agreed in all its characteristics with that upon admitted letters typed on his machine and this was one of the facts which led to his conviction.PRINTED MATTER.-Much of what has been said about the differentiation of typing applies also to printed characters. The founts used by different printers have distinctive differences and parts of certain letters tend to become defective with use. Evidence on such points is required when the authenticity of a printed document such as a passport (vide infra) is questioned. SEALs.-The methods of forging seals have been fully described by Turkel in his FiiZschungen p. 14 (cf. ANALYST 1931 56 141). Photographic methods can be used for detecting such forgeries and in some cases chemical evidence may be decisive. For example in the case of Rex v. Fink (1911) the defence set up in a case in which a cheque had been forged was that the forgery had been com-mitted after the cheque had been posted in a sealed envelope.Chemical tests, however were applied to the wax of Major Fink and to the seal on the letter, and gave practically identical results for colouring matter ash and sulphate, whereas the corresponding figures given by the wax from the post office where the letter was posted and by six samples of red sealing wax bought at random were tot ally different . STAMPS AND POSTMARKS.-AS an illustration of the kind of information that may be gathered by minute examination of the stamp and postmark on an envelope reference may be made to a case in which an anonymous letter bearing a German postmark and registration mark was received in a London office.Micro-scopical examination showed that only that part of the postmark upon the stamp was genuine the remainder of the circle upon the paper having been crudely completed. Ultimately it was found that the letter had originated from within the office and that the stamp and registration number had been detached from a genuine registered German letter (the receipt for which had been duly signed) and then put on to another envelope containing the anonymous letter after which the missing part of the postmark had been replaced by hand probably in Indian ink 152 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS COMPOSITION OF THE PAPER.-The composition of the paper of a document may give useful suggestions as in a case in 1914 in which the crudely forged notes of an Oriental bank were found to consist of pure flax.This suggested that the forgeries had probably emanated from Russia as was subsequently found to be the case. Chemical tests including the difference in the liberation (by the sizing) of iodine from potassium iodide and the determination of the acidity afforded proof that the forged American passport produced by the German spy Brekoff (alias Rowland) was not genuine and evidence to that effect was given at his trial in 1915. In addition to chemical differences in the papers the dyestuffs in the paper seals attached to the two documents were chemically different and there were differences in the type in which the passports were printed. Among the printing defects was one which could easily be seen by the jury for in the German version the American eagle had been docked of one of its tail feathers.There were also two other cases in which similar evidence was required. ARTIFICIAL WATERMARKS.-The usual method of fabricating a watermark is to stamp the paper with the required device in a wax medium. Such spurious watermarks can as a rule be removed by treating the paper with a suitable solvent, as was found to be possible with certain notes which were being widely circulated. The fraud can also generally be made manifest by examining the document in ultra-violet light when the artificial watermark will often show a pronounced fluorescence. CHARRED DOCUMENTS.-I have discussed the methods of deciphering charred documents in previous papers (Discovery 1924 5 336; ANALYST 1925 50 174).Photographic methods in which the charred fragment leaves an imprint of printed matter on a sensitised plate depend upon the fact that printing ink which has been burned produces certain products which reduce silver salts whereas charred cellulose has no action. In the communications mentioned above it was shown that different printing inks behave differently in this respect. The other method of deciphering charred fragments is to continue the cal-cination further for which purpose I have found the use of two pieces of wire gauze held in crucible tongs to be the most suitable since the calcination can be controlled so that a coherent ash of the required colour is left. The lampblack of printing inks being less combustible than the char of paper is left in its original black characters on white ash whilst the alumina forming the bases of coloured printing inks remains in white on dark gray or blackish ash.Ordinary writing ink leaves a brownish residue of iron oxide and the graphite of blacklead pencils and of copying ink pencils can be obtained as a residue on either white or grey ash. The reason why so little writing was visible in the charred fragments in the Wood case (sztpra) was that the pigment of the copying ink (Swan) pencil which had been used contained no graphite. This calcination method was found effective in a case in 1923 in which it afforded confirmation of the statement of a prisoner that he had accidentally burnt a bundle of bank notes of high value (cj.ANALYST 1925 50 178). Experiments made at that time showed that banknote paper contains so little filling material that it would be quite possible for a bundle of notes to be burnt and to leave very little coherent ash MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS 153 EVIDENCE ON HA4NDWRITING.-h the Podmore case as in many other cases, questions of the identification of handwriting were raised. Sooner or later every chemist who undertakes the scientific examination of documents will be faced with the difficulty that his work must be incomplete unless it also deals with the examination of the writing on the documents; in fact the Government Analysts of several of the Dominions and Colonies have been compelled by circumstances to take the subject of handwriting into consideration.In the interests of justice this is a move in the right direction for much of the obloquy attaching to hand-writing experts has been due to the fact that the earlier experts were frequently trained observers of minute detail (some were engravers) but they had not had a scientific training and thus were prone to draw deductions which were not warranted by the observed facts. For instance it was not uncommon for a hand-writing expert to swear positively in the box that a given piece of writing was written by a particular person whereas all that his observations justified was the inference that the characteristics of the writing agreed in form or writing habit with those of that person. Hence when (as sometimes happened) it was found that more than one person shared those characteristics a mistake had to be admitted, and discredit was brought upon the whole system of comparing handwriting.Essentially the judgment of handwriting is an analytical process and depends upon the same fundamental rules of inductive logic (isolate vary measure) as are used in chemical analysis but it is only exceptionally that a categorical conclusion can be drawn. The real value of the evidence is that it assists the Court to decide in which direction the balance of probability lies. For example in the Podmore case the demonstrable facts were that the characteristics of the writing on the dirty fragment of paper and of the indented writing in the order book agreed with those of admitted writing of the accused.If it was not his writing either it must have been a deliberate imitation of it or there must have been two persons writing in exactly the same way and having the same initials in the garage at Southampton at about the same time. It was for the jury to decide to what extent such a coincidence would be probable. Or again in the case of Archdeacon Wakeford the writing in the hotel register of the disputed words “and wife” agreed in all respects with admitted writing, even including the formation of a straight stroke as a sign for “and”-a habit which until it was discovered in a volume of his manuscript was unknown to those best acquainted with him. The only possible conclusion other than that the writing was that of the accused was that it was the work of an abnormally skilful forger and it was then for the Court to decide whether such a forger could have been present at the hotel on two unexpected occasions and could have added the words in such a way as to give the correct colour tones of the inks as well as to reproduce the exact formation and style of the genuine writing.TRACED FoRGERIES.-Exceptional~y it is possible to state a conclusion in more positive terms than has been indicated as for example in the case of Beckerkunst v. Cohen (1929) in which a forged will was produced signed in an abnormal way by a woman whose condition was proved by medical evidence to be such that firm writing such as that of the signature in the document would have been impossible. I 154 MITCHELL SCIENTIFIC DOCUMENTARY EVIDENCE I N CRIMINAL TRIALS this case the results of comparison of the signature on the will with other signatures of the deceased woman supplemented the medical evidence but there are instances when the evidence of documents by themselves may be conclusive.For example, in the case of Rex v. Henry (1929) a will was produced in terms which were practically identical with those on a draft of the will produced some months previously and then photographed. The formation of the words and their coincidence in position on the paper were explicable only on the assumption that one was in part a tracing from the other. When subsequently the production of the draft was again required a third document purporting to be this draft was produced. This differed materially from the original draft which had been photographed, and the space left where a piece had been cut from the edge of the former differed in size and shape from the corresponding space cut out in the latter; this space might have become larger in the interval between the times when the production of the draft will was demanded but it was an impossibility for it to have shrunk.On rare occasions the model which has served for a tracing may be discovered, and when it is it may convert probability into certainty.* The classic instance of this type of forgery is the American case of Rice-Patrick in which the signatures on four pages of a will agreed so closely with one another that it was obvious that they must have been tracings since no one would reproduce all the lines of the words in practically the same relative positions (see Osborn Questioned Documents p.293). When considering indications of tracing there is one possibility which must not be overlooked. Solicitors sometimes indicate by pencilling in a name the place on a document where the signature is required and sometimes a client whose intelligence is not of a high order will attempt to copy the pattern. In the case of Oliver v. Oliver (1930) there were features in a signature which had they been in a letter and not upon a legal document would have been conclusive that the signature was not genuine. The lines were wavering and hesitating there were frequent breaks in unusual places the formation of the letters was abnormal and there were traces of graphite at the edges of some of the strokes.The significance of these points however was discounted by the fact that none of them was inconsistent with the other hypothesis namely that they were the results of an attempt to make a slavish copy of a signature previously outlined by a solicitor in blacklead pencil. DISCUSSION Mr. A. LUCAS confirmed Dr. Mitchell’s statement that chemists who attempted to confine their work to the microscopical and chemical examination of documents were eventually compelled to take up the examination of handwriting. He gave a few examples of cases in his own experience illustrating points which had been raised in the paper. In one of the cases cited an ink that was alleged to be a mixed ink was proved not to be a mixture. In another case an anachronism was discovered in the composition of paper which contained wood cellulose, although the date upon the document was about 60 years before that material was used as an ingredient of paper. Mr. Lucas also confirmed the value of Osborn’s comparison microscope for the examination of documents. * In the case of Rex v. Brown (1931) which was sub judice when this point was mentioned, a signature showing indisputable indications of marks made with a dry point was found and the coincidence of this signature with one on the document in dispute was conclusive evidence that the latter was not genuine

ISSN:0003-2654    

DOI:10.1039/AN9325700144

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/AN9325700155

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

168 OAKLEY WOODS USED BY THE ANCIENT EGYPTIANS Woods Used by the Ancient Egyptians BY KENNETH P. OAKLEY As no one can hope to have specialised knowledge in all branches of science it is almost essential for the modern archaeologist to obtain the co-operation of technical experts. Is it too much to suggest that owners and curators of archaeological collections should have the materials of which their specimens are made scientifically examined so that the misleading statements at one time so common on museum labels might be avoided ? The accompanying photomicrographs illustrating the structure of two of the commonest woods employed by the ancient Egyptians, may be of interest to those engaged in such research on Egyptian materials. These photomicrographs show sections of specimens in my own collection.The sections were cut and examined for me by Mr. J. C. Maby then of the Forest Products Research Laboratory (Oxford Branch) by whose kind permission I am able to reproduce them. They illustrate a special application of the technique recently described by him (ANALYST 1932 3). FIG. 1.-A transverse section cut from a wooden model of a building-cradle (used in raising blocks of sto,ne) found in a “Foundation Deposit ” under the Temple of Queen Hatshepsut at Der el-Bahari and dating from about 1500 B.C. The wood is that of Ficus sycomorus (?) which was one of the most important indigenous trees growing in Ancient Egypt. Although this wood was extensively used in Egypt when small lengths only were required it has serious limitations, and its coarse grain and light spongy texture make it unsuitable for long straight planks or beams.The hulls of many Nile boats in Egypt were made of this wood, cut up into short rectangular blocks and built “brickwise.” FIG. 2.-A transverse section cut from a block of wood which originally formed part of the side of a Xth-XIth dynasty coffin (circa 2200-2000 B.c.) found at Der el-Bahari. The wood is coniferous and hence must have been imported from abroad. It is in fact almost certainly the wood of Lebanon cedar (Cedrzts Zibani Barrel). FIG. 3.-A transverse section from a piece of coffin wood (probably XIIth dynasty circa 2000 B.c.) which has also been identified as Ficus sycomorzcs ANCIENT EGYPTIAN WOODS Fig. 1 Fig. 2 Fig. 3 Fig. 1. Ficus sycomorus ( ?).Cut from near centre of tree. Transverse section x 50 linear. Fig. 2. Cedrus Zibani Barrel. Transverse section x 50 linear. Fig. 3. Ficus sycomorus. Cut from near the outside of the tree. Transverse section x 50 linear of these woods. Wood. Ficus sycomorus Ficus sycomovus Ficus sycomovus Cedrus libani Tamarix nilotica (a) Acacia seyal or Acacia PtiEoticn (Z) Buxus sempevvirens Tilia sp.* Fagus sylvat ica t OAKLEY WOODS USED BY THE ANCIENT EGYPTIANS 159 As Professor P. E. Newberry pointed out in his Presidential Address to the Anthropological Section of the British Association 1923 Lebanon cedar is not the durable and priceless wood that some writers have thought it to be although it was certainly superior to any wood native to Egypt itself and hence in ancient times formed relatively valuable timber.The wood is reddish in colour and has a silky grain. Never-theless it was one of Egypt’s most valued imports because the one thing that the country lacked was large timber. As early as the 1st dynasty coniferous wood (almost certainly Cedws Zibnni) was being shipped from Palestine to the Valley of the Nile and throughout Egyptian history the trade was continued with the result that Byblos the port of the Forest of Lebanon became one of the chief maritime trading centres on the Syrian coast. The following is a summary of the identifications of the woods from which the Egyptian specimens in my collection were made and I am much indebted to Mr. L. A. Boodle of Kew to Mr. J. C. Maby and to Mr. B. J. Rendle of the Forest Products Research Laboratory Oxford for their assistance in the identification It is apt to shrink and warp badly under some conditions. Object made of the wood. XIIth dynasty coffin XIIth dynasty tomb Model building-cradles X-XIth dynasty coffins Model mattock from Boning-rod with flax strihg Mummy labels with Greek Mummy label with Greek Mummy label with Coptic statuette D& el-Babarri script script script * Lime. f Beech. source Date about of the wood. 2000 B.C. Egypt. 1600 B.C. Egypt. 2000 B.C. Egypt. 2200-2000 B.C. Lebanon. 1500 B.C. Egypt. 1st cent. B.c.(?) Egypt. 3rd-4th cent. N. Africa ( ?!. A.D. ,* , Some country north of Egypt. D D ,* 8 D

ISSN:0003-2654    

DOI:10.1039/AN9325700158

出版商:RSC    

年代:1932

数据来源: RSC

摘要:

OAKLEY WOODS USED BY THE ANCIENT EGYPTIANS 159 A Simple Apparatus for the Rapid Determination of Combustible Vapours in the Atmosphere BY L. C. McNAIR B.Sc. AND H. C. GULL M.Sc. ASSOCIATED with the industrial use of inflammable organic liquids are frequently their poisonous character and the risks of explosion. It is useful therefore to have a simple and rapid method whereby the concentration of the vapour of such liquids present in the atmosphere of a room or tank may be determined with reasonable accuracy. For this purpose the Haldane apparatus (Foster and Haldane 1906, The Investigation of Mine Air p. 100) has been largely used. In order to meet the desire for an apparatus which embodies the principle of that of Haldane but is more portable the instrument to be described was devised.This matter was brought to our notice some three years ago and th 160 MCNAIR -4ND GULL A SIMPLE APPARATUS FOR THE RAPID present modification of the Haldane apparatus is the outcome of experiments made in this laboratory during the last two years. It consists of two glass vessels of approximately 100 ml. capacity one of known volume to contain the sample of air under examination (Vessel A Fig. l), the other a control vessel B. In Fig. 1 for the sake of clearness the manometer Fig. 1. Fig. 2. and burettes are shown displaced to the right whereas in the actual apparatus they are in front of vessels B and A respectively. Both vessels are immersed in a water-bath which is stirred by a current of air. The control vessel By is fitted with a stopcock C opening to the air and is connected with the sample vessel by the manometer M containing coloured water and the cock D.For the construction of the manometer capillary tubing of approximately 0.5 mm. bore is used and the two limbs are connected at their lower ends by a piece of rubber tubing bound with copper wire to prevent kinking. A small bulb of 0.5 ml. capacity is blown in the upper part of each limb to minimise the risk of the coloured water being drawn out of the manometer by a considerable difference in pressure between the two vessels. At its lower end the sample vessel A is fitted with an inlet tube and stop-cock E and at the top with an outlet tube and cock F. This vessel is i DETERMINATION OF COMBUSTIBLE VAPOURS IN THE ATMOSPHERE 161 connection with the manometer and with a graduated burette consisting of two branches; the larger with a capacity of 5.5 ml.is graduated in tenths of a ml., and the smaller with a capacity of 1 ml. in hundredths of a ml. A three-way tap €3 at the lower end of the double burette allows either section to be connected independently with the reservoir R. Mercury or water may be used in the reservoir and burettes. The overall dimensions of the apparatus are loin. x 5 in. x 3 in. It has been found advisable to have the arrangement for combustion as a separate entity. A side tube 1 cm. in diameter is sealed into the upper end of the sample vessel. Into this is ground a glass stopper G carrying a platinum filament together with its supports and electrical connections by means of which the inflammable vapour in the sample vessel is burned to carbon dioxide and water.Fig. 2 illustrates the construction of this stopper in greater detail. To the lower end of the stopper is sealed a short length of thin glass rod terminating in a hook from which is suspended another piece of rod to support the centre of the filament. The ends of the filament are twisted round two stout copper wires which pass to the interior of the stopper through two small holes in the glass one on either side of the support; there they are held in place by a small plug of plaster of Paris, followed by a non-porous layer of shellac cement or sealing wax of high melting point. The remaining space in the stopper which is open to the air may be filled with distilled water to keep the copper wires quite cold in use.Two springs are used to keep the stopper in place and a little tap grease is used as a lubricant to’ ensure a gas-tight joint. This arrangement allows the platinum filament to be easily replaced should a “ burn-out ” inadvertently occur. When carrying out an analysis all taps are opened and the reservoir R is lowered until the liquid level in the burette to be used is near the lower end of the burette. Taps D and H are then closed and the air under examination is aspirated through the apparatus by applying suction at F until the original air in the sample vessel has been replaced. It usually suffices to aspirate about 400 ml. Taps C E and F are then closed and D and H are opened. The water-bath is well stirred for a minute or so and the liquid level in the burette is adjusted so that the water levels in the two manometer limbs are equal.The burette reading is noted and taps D and H are closed. The filament leads are connected with a battery in series with a small variable resistance and the filament is raised to a dull red heat for five minutes. At the end of this period the current is stopped and the apparatus is allowed to cool for six minutes the water-bath being stirred meanwhile. Tap H is first opened and then D cautiously and the liquid level in the burettes is readjusted so as to bring the liquid levels in the manometer back to equality. It has been found that the times given are the least that are necessary to ensure satisfactory results. I t should be noted that a considerable pressure is developed in A during combustion and all taps must be closed and be quite gas-tight before switching on the current.In order to test the apparatus mixtures of benzene and air and of hexane and air in known concentration were prepared and examined in the following way: A suitable quantity of the liquid solvent was weighed in a thin-walled sealed In use it is essential that the insides of both vessels be kept moist 162 APPARATUS FOR THE RAPID DETERMINATION OF COMBUSTIBLE VAPOURS ETC. glass bulb and dropped into a clean dry bottle of 11,200ml. capacity together with 100 ml. of clean mercury. The bottle was fitted with a closely-fitting glass stopper (a gas-tight joint being ensured with a little tap grease) fitted with a three-way tap and held firmly in position with a clamp.Some two litres of clean air were then pumped into the bottle the tap closed and the bottle shaken vigorously until the glass bulb was broken. A small mercury manometer was connected with the bottle and the pressure in it was measured. The bottle was then connected with the inlet tube of the analysis apparatus by means of a short length of glass tube rubber connections being reduced to a minimum and the gas in the bottle was allowed to flow through the combustion vessel replacing the air therein. An analysis was then carried out as described above. The composition of the gas issuing from the bottle was calculated from the weight of solvent used, capacity of the bottle pressure and temperature of the gas in the bottle and the barometric pressure.It was found that the inflammable vapour in these mixtures was partly removed by contact with rubber or water. Results of these test analyses are given below. In blank tests a contraction of 0.01 per cent. was always obtained. This was due not to leaks but possibly to the formation of oxides of nitrogen since after combustion these were detected in the air from the combustion chamber. A% deduction was made from all observed contractions to allow for this small error. RESULTS OF ANALYSES Substance. Calciilated. Per Cent. (by vol.). Benzene 1.18 , 0.807 1 0.023 8 0.107 3 0.025 Hexane 1 *05 Found. Per Cent. (by vol.). 1-18 0.816 0.022 1-04 0.107 0-025 Contraction observed in vessel of 98 ml., less 0.01 ml. ml. 2.90 2.00 0.055 4.56 0.470 0.110 The results agree with those calculated. Quantities greater than 2.5 per cent. of benzene or 1.2 per cent. of hexane could not be determined as a contraction greater than 5.6 ml. could not be measured in our burette. Mixtures rich in inflammable vapour should first be tested in a stout glass bulb, fitted with a stout filament for firing to see if an explosion is possible. In conclusion it may be stated that several forms of this apparatus were constructed and found unsuitable in one respect or another. Among these was an apparatus with a brass combustion chamber which gave consistently high results, due to interaction between carbon dioxide and the walls of the vessel in the presence of moisture. We desire to tender our thanks to the Government Chemist for permission to publish this work. THE GOVERNMENT LABORATORY, CLEMENT’S INN PASSAGE STRAND W.C.2

ISSN:0003-2654    

DOI:10.1039/AN9325700159

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/AN932570163b

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/AN9325700164

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/AN9325700168

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/AN9325700173

出版商:RSC    

年代:1932

数据来源: RSC