摘要:

MAY, 1908. Vol. XXXIII., No. 386. THE ANALYST. OBITUARY. JAMES BELL, C.B., D.Sc., F.R.S. THE recent announcement of the death of Dr. James Bell, at the advanced age of eighty-four, will necessarily have recalled to those readers of the ANALYST who remember the early history of the working of the Sale of Food and Drugs Act many incidents that have gradually grown dim during the fourteen years in which the veteran chief of the old Somerset House Laboratory has lived on in peaceful enjoy- ment of the retirement into which he has been followed by most of those who acted as senior members of the staff of which he w a ~ the principal-principal, perhaps, towards the end rather de jure than de fucto. To chronicle his passing away in the official journal of the Society of Public Analysts without some reference to the past would be incongruous and even disrespectful to his memory, especially as the time has come when it can be looked back at dispassionately and without any unkindly thought towards the memory of one who was in himself always the personification of kindliness.When Dr. Bell succeeded to the headship of the Somerset House Laboratory, the law had but recently created a new body of officers to watch over the purity of the nation's food at a time when, despite the admirable pioneer work of Hassall and Letheby, comparatively little was known about its chemistry, and when adulteration must have been very rife indeed. Not a few of the appointments to Public Analyst- ships made under the Adulteration of Food Act of 1872 were more or less forced on looal medical officers of health who had had practically no training in analytical ohemistry, and there can be no doubt that here and there men were appointed who were not only ignorant of the work they had to do, but unfitted by their experience and by their education to acquire the skill necessary to cope with it.I t became clearly necessary that there should be something in the nature of a court of analytical appeal for those who ahallenged the certificates of adulteration issued against them, and the Sale of Food and Drugs Act of 1875, which succeeded the short-lived Act of 1872, threw the duty of referees upon the staff of the Somerset House Laboratory. I t was, rightly or wrongly, the opinion of the majority of Public Analysts of those days that Dr.Bell and his colleagues failed to realise completely that their positions were those of impartial referees, appointed to assist the magis-158 THE ANALYST. trates, and that the attitude they were apt to assume was, in effect, apt to incline too much towards that of e z parte advocates statutorily retained for the defence. If there was exaggeration in this opinion, a dispassionate and competent chemical historian, undertaking a revision of all that happened in that troubled period, would probably find himself obliged to admit that it had a substratum of truth. There were then not even such isolated statutory regulations as now exist for guidance in reporting on milk and butter, and the Public Analyst had for these, as for all other products, to make his own standards or limits.He made them as well as he could, and in his informally corporate form (as the Society of Public Analysts) he eventually succeeded in laying down limits for milk which, after long years of hard fighting and after various public inquiries, he has now had the satisfaction of seeing fully ratified by Government under the statutory powers conferred by more recent legislation on the Board of Agriculture, The law now definitely states that milk falling below certain statutory requirements shall be deemed to be adulterated unless the contrary be proved. This statement probably presents itself to the common wind as merely an explicit and definite expansion of what was less definitely but implicitly provided in principle in the Sale of Food and Drugs Act of 1875.Without some such assumption the Act would have been more or less waste paper. But the view which appeared to be held by the Government referees of earlier days was rather the converse one-that any sample of milk ought to be regarded as genuine in the absence of extrinsic proof to the con- trary, provided that its deficiency in the natural constituents of milk did not exceed the abnormal limits sometimes reached by the milk of exceptional cows under excep- tional conditions. The Public Andyst, therefore, who certified adulteration in any but a very bad case was Gable to have his finding met by the familiar statement that the Somerset House analysts were unable to affirm ” his conclusion, even when (as was unfortunately not always the case) they agreed with his analytical data. The consequence was that, except when the Public Analyst was fortified by the very full confidence of his public authority, the faithful discharge of his duty often put a con- siderable tax on his moral courage ; and the attitude of (‘ Somerset House ” towards milk adulteration became well known and appreciated in the milk trade.Indeed, a milk vendor, charged with watering, was once heard in court by the writer of this notice, while pleading ( ( not guilty ” to the full charge, to naively add that he had put in no more than ‘‘ the Government allowance.” Perhaps it was to some extent the ineffective drafting of the Act of 1875 which led to the unfortunate difference which prevailed between the views taken as to its administration by the Public Analyst on the one hand and by Dr.Bell and his colleagues on the other. At all events, the official attitude which sprang up was one unhappily inclining more towards hostility than towards co-operation. I t must be acknowledged that Dr. Bell began his duties under the Aot by undertaking a not inconsiderable amount of investigation, which culminated in a treatise on food analysis which contained much that was useful, though perhaps not a great deal that was new; and we are afraid that it must be recorded that, notwithstanding its staff and its resources, the laboratory over which he presided made under his direction but few fundamental contributions towards the rapid and brilliant advancement of food analysis which then began and which has proceeded steadily ever since.This comparative aloofness on the part of a Govern-THE ANALYST. 159 rnent Department from public contribution to the work which was so enthusiastically pushed forward in private laboratories was felt to widen the breach between those who should have been able to regard each other as colleagues, and the position some- times led in hot blood to very regrettable recriminations on both sides, which neither side could now altogether justify in the mood of calm retrospect. The very fact that it is dificult to write or think of the question except as one involving ‘( sides,” when there should have been but common interest for the public weal, is sufficient to in- dicate the unhappy falsity of the whole position. Nevertheless, through all the troubles of that troublous time Bell retained the friendship and regard of many of those who felt most forced to regard his Department as non-progressive, and even at times obstructive; and there is probably no one left of those who were wont to be occasionally brought in conflict with it who has anything but kindly thoughts towards his personal memory.On his retirement a new Government Laboratory, directed by a new chief wisely chosen from the ranks of advanced science and free from the trammels of traditional officialism, arose on the ashes of the old one, and before many years had gone by the relations between Public Analysts and the official referees underwent a happy and progressive change, which has culminated in a position of co-operation and of mutual confidence, to the advantage of the public as well as of those engaged in the administration of the law ; and no one will have been more gratified than the subject of this notice to look on, from his retirement, at the gradual growth of peace and harmony where formerly, under his, at least titular, generalship, there had been much battle, in which he bore his own part, if not altogether blamelessly, at least free from any conscious sense of blameworthiness. His position as referee under the Sale of Food and Drugs Act.covered, of course, but a small part of the very multifarious duties which fell to him in connection with the work of his Department, as is evidenced by even a casual glance at any of his long series of annual departmental reports.He first entered the Inland Revenue Department in 1846, after a course of scientific study at University College, London, and in 1867 became Deputy-Principal of the Somerset House Laboratory, succeeding to the prinoipalship in 1874, on the death of the late Mr. Phillips. In addition to directing the large staff of the laboratory with its many branches, he served from time to time on various Departmental Committees, and his services to the nation were publicly reeognised by his appointment to the Companionship of the Order of the Bath and by his election to the Fellowship of the Royal Society; while the Royal University of Ireland accorded him the honorary degree of Doctor of Science. From 1888 to 1891 he served as President of the Institute of Chemistry, in succession to Professor Odling, and in 1894, at the age of seventy, he retired from official life, spending the remainder of his days in quiet retirement at Hove. He leaves one son, Sir W, J. Bell, who was for some years an Alderman of the London County Council. B. D.

ISSN:0003-2654    

DOI:10.1039/AN9083300157

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

160 THE ANALYST, THE VOLUMETRIC DETERMINATION OF REDUCING SUGARS. Part 11.-The Limits of Accuracy of the Method under Standard Conditions. BY ARTHUR R. LING, F.I.C., AND G. CECIL JONES, S.C.G.I., F.I.C. (Read at the X e c t i i i g , Marcl~ 4, 1908.) IN a previous paper one of us and T. Rendle brought forward a modification of the method of estimating reducing sugars by titration with Fehling’s solution, based on the use of a new indicator, ferrous thiocyanate (ANALYST, 1905, 30, 182). The method was recommended mainly on account of its greater accuracy as compared with the one usually adopted of titrating sugars with Fehling’s solution, in which a solution of potassium ferrocyanide acidified with acetic acid is used as indicator. Daily experience of this modification of the volumetric method since the previous com- munication was published has confirmed the view that in practised hands it is capable of yielding results little, if at all, inferior in accuracy to those obtained by the gravimetric method; still, in order to establish once for all its limits of accuracy, it.THE ANALYST.161 seemed desirable to submit it to a stringent critical investigation. In carrying out the experiments necessary for this work, we have to acknowledge the assistance of Messrs. T. Rendle, G. McLaren, and R. C. Denington, and take this opportunity of thanking these gentlemen. The Indicator.-In the previous paper a misprint in the directions given for preparing the indicator was overlooked, and this, we fear, may have led many workers to abandon all attempts to use the method.The amount of hydrochloric acid pre- scribed should have been 5-0 c.c., and not 50 C.C. (Zoc. cit., p. 184). Such a high proportion of acid a8 this renders the indicator absolutely unworkable. Recently we have carried out a series of experiments in order to determine the effect of varying the constituents on the sensitiveness or otherwise of the indicator. As a result of these, we find that hydrochloric acid is the most satisfactory acid to employ, but that for the quaratities of the other constituents previously given 5.0 C.C. is too much. Better results are obtained when the amount of acid is decreased and that of ammonium thiocyanate increased. We find that the following proportions give the most satisfactory indicator : Ammonium thiocyanate ...... ... ... 1.5 gram. Ferrous ammonium sulphate ... ... ... 1.0 ,, Ordinary concentrated hydrochloric acid ... ... 2.5 C.C. Water.. . ... ... ... ... ... 10.0 ,, As previously stated, it will usually be necessary to decolorise the indicator by the addition of a trace of zinc dust immediately after its preparation, and again after it has been kept for some time. When decolorised too often in this way, the indicator loses sensitiveness. Before commencing the titration, about a dozen small drops of the indicator should be placed on a glazed porcelain or opal glass slab. A drop of the assay liquid should then be removed from the titration-flask and brought in contact with the middle of one of the drops on the slab. If the margin of the drop of indicator is touched with the assay liquid, the results are less satisfactory, possibly because of the greater risk of aerial oxidation.I n any case, it is necessary to perform the test as rapidly as possible. The various sugars used for the determinations to be described were all of high purity and practically free from ash. The dextrose, laevulose, and maltose were specially prepared for the purpose of another piece of work to be published by L. Eynon and J. H. Lane in conjunction with one of us. The dextrose wa8 prepared by hydrolysing cane-sugar with an acid. The product was repeatedly recrystallised from alcohol until the rotation was constant. The final specific rotatory power (c = 8) was [u],, 1 7 ~ + 52-65', The laevulose was prepared from Schering'e com- mercial product.This, after being many times recrystallised from alcohol, had a constant specific rotatory power (c = 10) [.ID- 18.50 - 93.83O. The maltose was pre- pared by J. L. Baker's method by the action of barley extract on soluble starch (Jown. Chem. SOC. Trans., 1902, 81, 1177). I t was repeatedly recrystallised from 80 per cent. alcohol, the specific rotatory power being determined after each recrystallisation on a portion kept in a vacuum over sulphuric acid until its weight was constant. Rzferred to the anhydrous sugar, the final value obtained (c=6)162 THE ANALYST. was [.II, 17.50 137.8", a value substantially identical with that of Brown, Morris, and Millar (Journ. C'hem. SOC. Traits., 1897, 71, 112). Instead of weighing out definite amounts of dextrose, lsvulose, and maltose, the purified sugars were dissolved in water to a concentration of about 6 grams per 100 C.C.The exact concentration in grams per 100 fluid grams was then determined from the specific gravities of the solutions at 15*5°/15*50 by means of the solution factors determined recently by L. Eynon and J. H. Lane in conjunction with one of us; this work will be published later on. Quantities of the solutions corresponding with the required weights of the several sugars were then accurately weighed out and made up to the necessary volume. The invert sugar was made by hydrolysing pure sucrose with hydrochloric acid in the manner described in the previous paper (Zoc. cit.). It will be seen that the values given for invert sugar so prepared are substantially the mean of those obtained with dextrose and lievulose (compare, how- ever, below).I n the paper by one of us and Rendle, previously referred to, the weight of the various reducing sugars equivalent to 10 C.C. of Fehling's solution was given. I t was known that this quantity varied slightly with the concentration, and it was therefore recommended that the concentration of the sugar solution should be so adjusted that 20 to 30 C.C. were required to reduce 10 C.C. of Fehling's solution. The varia- tion of the reducing power due to varying concentration has now been determined with some accuracy, which extends the range of concentration of solutions which can be directly titrated and increases the possible accuracy of any results obtained by the method.Solutions of invert sugar, of dextrose, of lawulose, and of maltose, prepared ac1 above described, were titrated against 10 C.C. of Fehling's solution, with the following results : 1)es trose. Lzv\-nlose. - h A. 13. c'. B. c. 0.125 41.0 195.1 44.2 181.0 0.15 33.8 197.2 35.9 185.7 0.20 24.6 203.2 26% 188.0 0.25 19.4 206.2 21.4 -186.9 Invert. A. 13. C. 0.125 42.4 188-7 0.15 34.7 192.1 0.20 25.7 194% 0.25 20.2 198.0 0.30 0.35 - - 0.40 - - - - JIaltose. 7-' - - 13. c. - - - - 40-7 122.9 32.6 122.7 27.15 122.8 23.3 122.6 20.55 121-7 Column A gives the concentration of the sugar solutions in grams per 100 C.C. Columns B give the C.C. required by 10 C.C. of Fehling's solution. Columns C give the C.C. of Fehling's solution equivalent to 1 gram of sugar. When these numbers are plotted on squared paper, with the concentrations for abscisse, and volumes of sugar solution for ordinates, curves are obtained which, like those given by Brown, Morris, and Millar (Jouru.Chem. SOC. Trans., 1897, 71, 280),THE ANALYST. 163 connecting weight of sugar present with copper oxide reduced under their standard conditions, entirely fail to discover the errors of observation. When, however, the concentration is plotted against the volume of Fehling’s solution equivalent to 1 gram of sugar, the errors are greatly magnified and their extent can be measured. We are only justified in drawing the straight line which makes the sum of the errors of observation least. This we have done, and from it have obtained the numbers given in columns L’, D’, 1’, and M’ of the accompanying table.The plotted results are not of sufficieut importance to justify the expense of reproduction, but the limits of accuracy of the volumetric method can be ascertained by plotting the first and last of these numbers against the corresponding concentrations, and drawing the straight line joining them. If, then, our experimental numbers are plotted on the same paper, it will be found that on the average they deviate from these straight lines by 1 in 400 in the case of dextrose and invert, 1 in 300 in the case of maltose, and 1 in 100 in the case of Iawulose. The lsevulose values are not good, but the mean line drawn through the points is probably determined with some accuracy, as the calculated invert curve-that is, the curve occupying the mean position between the dextrose and lEevulose curves-is a line exactly parallel to the invert curve con- structed from direct experiments and lying very close to it.The invert table has been constructed from the mean of the calculated and directly-determined invert curves. I n the case of maltose we have felt that the only reasonable conclusion to be drawn from our experiments is that for all practical purposes within our limits of concentration the reducing power is a constant. We have, therefore, drawn not the straight line which makes the sum of the errors of observation least, as this would show the reducing power very slightly falling with increasing concentration, but the horizontal straight line which best satisfies this condition. The average error of the method is thus seen to be about 1 in 300, and with the exception of the lamdose numbers, no single observation of ours shows an error so great as 1 in 200.Brown, Morris, and Millar (ibid., 1897, 71, 106) place the maximum experimental error by the gravimetric method for maltose at 0-5 per cent. In their paper dealing with the constants of dextrose, lamdose, and invert sugar (ibid., 1897, 71, 275), they do not discuss the limits of accuracy of their work, which, however, we may assume, represented the highest order of accuracy of which the gravimetric method is capable. Long ago we were struck by the apparently anomalous variation of the numbers in the columns heEtded ‘‘ CuO corresponding to 1 gram ” sugar in the table given by Brown and his co-workers (Zoc.cit., 281). We accordingly plotted these numbers against the amounts of dextrose and Izvulose, and obtained a strange arrangement of points-strange, that is, because the table from which they were taken was not a statement of experimental results, which might well have yielded an irregular figure, but a calculated table for practical use, presumably derived from a smoothed-out curve or calculated equation. We can only conclude that they were derived from the curve connecting weight of sugar present with weight of copper oxide reduced, which, as we have said, is incapable of discovering experimental errors. We next plotted the actual experimental numbers of these workers and compared the amount of sugar present, not with the amount of copper oxide reduced, but with the amount of copper oxide reduced per gram of sugar in varying concentration-that is to say, we subjected their results to the same164 THE ANALYST. rigid test which we applied to our own.By grouping the results of these authors there are obtained four points on a curve in the case of laevulose and five points in the case of dextrose, and from these we are enabled to judge of the limit of accuracy of the gravimetric method in their hands. The average error in the case of dextrose appears to be 1 in 250, in the case of lmulose 1 in 300, and the maximum errors about 1 in 150. This is in close agreement with the limit they themselves place on their maltose values-0.5 per cent. Had we not overlooked that statement, we might have been saved the analysis of their results, which were undertaken with a view to determining how far, if at all, the volumetric process fell in accuracy below the gravimetric under the best conditions.The curves which we have been at the pains t o draw, however, place it in our power to recalculate the table of Brown, Morris, and Millar (Zoc. cit., 28l), and perhaps it may be worth while to extend the same treatment to the maltose table (Zoc. cit., 100). We think we have said enough to show that in our hands thevolumetric method is not only much more rapid, but quite as accurate, as the gravimetric method, to which some workers appear to cling because of the seeming accuracy of a method which gives a precipitate which, however incomplete, can be weighed accurately to 1 in 2,000.Although we have confined our experiments on the development of the volumetric method to the case in which 10 C.C. of Fehling's solution are employed, there are circumstances in which it is desirable to work with a greater or lesser volume of Fehling's solution. I t is interesting to note that, assuming the concentration of the sugar solution to be constant, the number of c.c.'s required for any titration is directly proportional to the volume of Fehling's solution employed-at all events, when this lies between the limits of 5 and 20 C.C. The experiments given in the following table prove this. Volumes of Fehling's solution varying from 5 to 20 C.C. were measured out, and in order to eliminate any possible error due to measurement, these volumes were also weighed and the volume calculated from the weights and the specific gravity of the Fehling's solution, which at 15-5"/15.5" was found to be 1-1618.Experiments with a solution of invert sugar (c = 0.2 gram) titrated against varying volumes of Fehling's solution : A 5 5 10 10 15 15 20 20 B 5.831 5.780 11.601 11.596 17.376 17.448 23.232 23.202 C 5.019 4.975 9.985 9.980 14.956 15.018 19-99 19.97 D 12.9 12.8 25-7 25-7 38.6 38.6 51.3 51.4 E 194.6 194.3 194.9 194.1 193.7 194.6 194.8 194.3 Column A gives the volumes of Fehling's solution as measured out with a Column B gives the weight in grams of the volumes under A. Column C gives the volume in C.C. (fluid grams) calculated from the weights pipette. under B and the specific gravity of Fehling's solution at 15*5"/15*5".THE ANALYST.165 Column D gives the volume of sugar solution in C.C. required for the titration. Column E gives the C.C. of Fehling's solution equivalent to 1 gram of invert sugar calculated from columns C and D. We work with vessels graduated to contain grams of water at 15.5" C., but for the volumetric method it does not matter which system of graduation be adopted, provided the flasks and burette agree. Nor does it matter that a 10 C.C. burette fails to deliver 10 C.C. of a viscous liquid such as Fehling's solution, provided the same pipette be used in standardising and in analytical work. Every preparation of Fehling's solution will need standardising, and this can be easily and quickly conducted under the exact conditions in which it will be used. Our work was carried out with a preparation of Fehling's solution of which 10 C.C.required under our conditions 25-65 C.C. of a, 0.2 per cent. solution of invert sugar, and the table we give is constructed on this basis. Volumc of Solu tioii required by 10 C.C. l~eliling's S o h tion. C.C.. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 ~ DEXTROSE. Gra111, 0-2427 0.2332 0,2226 0.2138 0,2056 0.1981 0.1911 0.1846 0.1784 0.1728 0.1675 0.1625 0-1577 0.1532 0.1490 0.1450 0.1412 0.1377 0.1343 0.1310 0-1 279 - - - C. c. 206.0 205.1 204.2 203.4 202.6 201.9 201.3 200.7 200.1 199.6 199.1 198.6 198.2 197.8 197.4 197.0 196.7 196.4 196.0 195.8 195.5 - - - LEVU LOSE. Gram. - - 0.24 11 0.2312 0.2222 0.2138 0-2060 0.1988 0.1921 0.1857 0-1798 0-1743 0.1691 0.1642 0.1596 0.1552 0.1511 0-1472 0.1 435 0.139 0.1366 0.1334 0.1298 0.1274 C.C.- - 188.5 188.0 187.5 187.1 186.7 186-3 186.0 185.6 185.4 185.1 184-8 184.6 184.3 184.1 183.9 183.6 183.4 183.3 183.1 182.9 182-8 182 6 INVERT SUGAR. Cram. 0,2412 0.2311 0.2218 0.2132 0.2052 0.1980 0.1910 0.1846 Oe.1787 0.1731 0.1678 0.1629 0.1583 0.1539 0.1497 0,1458 0.1421 0.1385 0.1349 0.1319 0.1288 0.1259 - - C . C . 197.5 196.8 196.0 195.5 194.9 194.3 193.9 193.4 193.0 192.5 192.2 191.8 191.5 191.2 190*9 190.6 190.3 190.1 189.8 189.6 189.4 189.2 - - Gmni. 0.3888 0.3711 0.3550 0.3402 0.3266 0.3140 0.3023 0.2915 0.2815 0.2721 0.2633 0.2551 0.2474 0.2401 0.2332 0,2268 0.2206 0.2148 0.2093 0.2041 - - - 122.5 -166 THE ANALYST. If any other worker finds that 10 C.C. of his Fehling’s solution require under his conditions only 25 C.C.of, 0.2 per cent. invert sugar, to use our table he will need to reduce the numbers in columns D, L, I, and M, and increase those in columns D’, L’, 1’, and M’ proportionately. These numbers have been given to four significant figures; the fourth, on our own showing, has no claim to accuracy, but is given to enable the third to be selected accurately when interpolating. I n practice, for example in the analysis of a mixture of dextrose and lmulose, or of dextrose and maltose, it will be sufficiently accurate to take the factor (c.c. Fehling’s solution per gram sugar) to the nearest third place; the maximum error which can be thus introduced is 1 in 250, and will usually be much less. Suppose a, solution of pure laevulose is being examined, and that 25-0 C.C.of it am required to reduce 10 0.c. of Fehling’s solution. Opposite 25 in the first column is found 0.2138 in column L ; the percentage of laevulose in the solution titrated is thus given direct. If 25-2 c.c., or other quantity not a whole number, is required to reduce 10 C.C. of Fehling’s solution, the percentage of lmdose can be easily found by inter- polation between the numbers in column L. The numbers in columns D’, L’, 1’, and M’ are given for another purpose- namely, the separate determination of two reducing sugars in a mixture, by a modification of the method of Morris (Jozcm. Fed. Inst. Brewing, 1898, 4, 162), which depends on the reducing power and the reading in the Ventzke-Scheibler half-shadow polarimeter, when observed in a 200 mm.tube in 10 per cent. solution. An illustra- tion will again best explain this use of the table. A commercial invert sugar gave a reading in 10 per cent, solution in a 200 mm. tube of - 4.7 divisions, and 10 C.C. of Fehling’s solution required 36-45 C.C. of 0.20 per cent. solution for reduction. After hydrolysis with acid only 35-95 C.C. of 0.20 per cent. solution were required to reduce 10 C.C. of Fehling’s solution. The difference between this reading and the last gives the amount of cane-sugar present in terms of invert sugar. From the table, column I, we find 36-45 C.C. =0.1441 per cent., and 35.95 C.C. =0.1460 per cent. The 0.20 per cent. solution of the sample under examination therefore contains cane- sugar equivalent to (0.1460 - 0.1441) = 0.0019 gram invert sugar-that is to say, (0.0019 x 0.95) = 0.0018 gram cane-sugar, or 0.9 per cent.on the sample. A 10 per tent. solution of the sample after fermentation gave a reading in a 200 mm. tube of -0.1 division, and 40.0 C.C. were required to reduce 10 C.C. of Fehling’s solution. Opposite 40 C.C. in colunin I we find 0.1319, the reducing power in terms of invert of the unfermentable residue in 10 per cent. solution. I n 0.20 per cent. solution, therefore, the unfermentable matter would raise the apparent content of invert sugar 0.0026 per cent. In a concentration such that 10 C.C. of Fehling’s solution require from 36 to 37 c.c., a difference of 0,0037 per cent. of invert sugar makes a difference of 1 C.C. in the burette reading; unfermentable reducing sub- stances equivalent to 0-0026 per cent.invert would tberefore reduce it 0.70 C.C. Ten C.C. of Fehling’s solution would therefore require (36.45 + 0.70) = 37.15 C.C. of the 0.20 per cent. solution if this were free from unfermentable reducing substances, or 1 gram of the sample contains dextrose and laevulose equivalent to 10+(37.15 x 9.002) = 10~0.0743 =- 134.6 C.C. Fehling’s solution. The manner of using the table is best explained by an illustration;THE ANALYST. 167 In concentrations such as that in which our first reduction experiment W&8 made-namely, where 10 C.C. Fehling’s solution require 36.45 C.C. of sugar solution- 1 gram dextrose = 196.6 C.C. Fehling’s solution, and 1 gram lavulose = 183.8 C.C. Fehling’s solution (columns D’ and L’) ; but 1 gram of our sample requires 134.6 C.C. Fehling’s solution. If we represent the percentage of dextrose in the sample by D and the percentEtge of Itevulose by L, we have the equation- 1.966 D + 1.838 L = 134.6( 1). The sample was found to contain 0.9 per cent. cane-sugar ; a 0.09 per cent. solu- tion of cane-sugar gives a reading of (3.85 x 0.09) = + 0.3 division when read in a 200 mm. tube in the Ventzke-Scheibler polarimeter. The actual reading ( - 4.7) must therefore be corrected for this amount as well as for the reading of the unfermentable residue ( - 0*1), in order to arrive at the reading due to the dextrose and Iaevulose alone - 4.7 - 0.3 - ( - 0.1) = -- 4.9 divisions, Since 1 per cent. solutions of dextrose or Izvulose give readings of 3.05 and -5.32 divisions respectively, we have 0.305 D - 0.532 L = 4*9( 2). From equations (1) and (2) D = 39-0, L = 31.5 per cent.

ISSN:0003-2654    

DOI:10.1039/AN908330160b

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 167 THE VOLUMETRIC DETERMINATION OF REDUCING SUGARS. Part 111.-The Determination of Sucrose and Invert Sugar in Mixtures. BY ARTHUR R. LING, F.T.C.,ANL) THEODORE RENDLE. (Read at the Meeting, Jfarch 4, 1908.) IT is well known that sucrose, although by constitution a non-reducing sugar, does reduce Fehling’s solution to some extent when boiled therewith, and that in mixtures of sucrose and invert sugar, such as raw sugars, cane molasses, and cane syrups, it is necessary to apply a correction when estimating the invert sugar in these by any method involving cupric reduction. Tables giving corrections for the influence of sucrose in mixtures of the two sugars referred to have been drawn up by Meissl, Zulkowski, Herzfeld, and by others. These corrections, however, refer specially to the particular modifications of the cupric reduction method used in each case.Since, however, the determination in question is purely empirical, each modification of the method requires its own table of corrections. In the present paper we place on record the data necessary for correcting the results obtained by the method previously described by us (ANALYST, 1905, 30, 182). The invert sugar used in the xperiments was prepared by hydrolysing sucrose with hydrochloric acid in the manner previously described (Zoc. cit.). The sucrose employed was of high purity. The ash content was practically nil, and the reducing power, per se, equal to less than 0.04 per cent. of invert sugar.168 THE ANALYST. I n the following tabulated results : Column A gives the amounts in grams of sucrose present in 100 C.C.of the sugar Column B gives the percentages of sucrose present expressed on the total Column C gives the percentages of invert sugar present expressed on the total ColumnjD gives the number of c.c.'s of sugar solution required to reduce 10 C.C. Column E give8 the percentages of invert sugar on the total sugars found by Column F gives the differences between the values given in columns C and E. The values given under column D are in each case the mean of at least two solutions. sugars. sugars. of Fehling's solution. direct experiment. determinations differing by not more than 0.1 C.C. made by different observers. TABLE I. Each solution contained, in addition to the sucrose shown under column A, 0.15 gram of invert sugar per 100 C.C.No. of Exlieriment. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12, A. Nil 0.005 0.025 0.05 0.10 0.25 0.50 1 *oo 2-50 5.00 10.00 15-00 B. Nil 3.2 14.3 25.0 40.0 62.5 "(3.9 86.9 94-3 97 4 98.5 99.0 C. 100.0 96.8 85.7 75.0 60 -0 37.5 23.1 13-1 5.7 3.0 1-5 1.0 D. 34.70 34.70 34.70 34.60 34.45 34.20 33.75 33-05 32.85 31.90 31.25 29.75 E. 100.0 96% 85.7 75.1 60.3 37.9 23.7 13.7 5.92 3.26 1.67 1.17 F. Nil Nil Nil 0.1 0.3 0.4 0.6 0.6 0.22 0.26 0.17 0.1'7 The conwntration of the invert sugar solutions in Table 11. is that at which we prefer to work-namely, 0.2 gram per 100 c.c.--and the experiments recorded in this table are in consequence more numerous than those in the others. A critical examination of the results given in Table 11. shows that the influence of sucrose is practically negligible until the proportion on the total sugar amounts to 30 per cent.(see column B), at which point the invert sugar is over-estimated by 0.2 per cent. This influence of sucrose increases progressively in the same direction until the proportion, expressed on the total sugars, 99.3 per cent., is reached, beyond which it has not been determined (see tho Iast result of the series). At this point the invert sugar is over-estimated to the extent of about 15 per cent. I t mustTHE ANALYST. 169 be remembered, however, that the magnitudes representing the percentages of invert sugar decrease as those representing the percentages of cane-sugar increase, and it will be seen that the correction to be applied is actually the greatest when the percentage of mcrose on the total sugars is between 50 and 80.In the case of a mixture of equal parts of sucrose and invert sugar, the latter would be returned as 50.4 per cent., instead of 50 per cent.-that is to say, it would be over-estimated by 0.8 per cent. ; whilst in the case of a mixture of sucrose 99 parts and invert sugar 1 part, the latter would be returned as 1.14 per cent., instead of as 1 per cent.; or, in other words, it would be over-estimated by 14 per cent. TABLE 11. Each solution contained, in addition to the sucrose shown under column A, 0.2 gram of invert sugar per 100 C.C. No. of Experiment. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26, 37. 28. 29. A. Nil Nil Nil Nil 0.01 0.03 0.05 0.10 0.20 0.30 0.40 0.50 0.60 0.70 090 1-25 1 -50 1-75 1-75 2.00 2 *oo 2.50 3.00 5.00 7 .OO 10.00 20-00 25.00 30.00 B.Nil Nil Nil Nil 4.8 13.0 20.0 33.3 50.0 60.0 66.6 71.4 75.0 77.7 80.0 86.2 88.2 89 -7 89.7 90.9 90.9 92.5' 93.8 96.1 97.2 98.0 99.0 99.2 99.3 C. 100.0 100*0 100.0 100.0 95.2 87.0 80.0 66.7 50.0 40.0 33.4 38.6 25.0 22-3 20.0 13.8 11.8 10.3 10.3 9.1 9.1 7.5 6.2 3.9 2.8 2.0 1.0 0.8 0.7 D. 25.65 25.65 25.60 25-70 25.60 25.60 25.60 25.55 25.45 25.40 25.55 25.30 25.20 25.15 25.10 25-05 24.95 24-85 24.80 24.70 34.80 24.80 24.70 24.20 23.60 92.95 83-40 22.25 22-25 E. - - - - 9530 87.10 80.10 66.90 50.40 40.40 33.80 29-00 25.40 22-70 20-40 14.10 12.10 10.60 10.60 9.45 9.41 7.76 6.44 4.05 3.04 2.23 1-14 0.92 0.80 F. - - - - 0.10 0.10 0.10 0.20 0.40 0-40 0.40 0.40 0.40 0.40 0.40 0.30 0.30 0.30 0.30 0.35 0.31 0.26 0.24 0.15 0.24 0.23 0.18 0.12 0.10170 THE ANALYST. TABLE 111.Each solution contained, in addition to the sucrose shown under column A, 0.25 gram of invert sugar per 100 C.C. No. of Experinien t. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. A. Nil 0.01 0.05 0.50 1.00 5.00 10.00 15.00 20 00 25.00 0-10 B. Nil 3-8 16.6 28.3 66.6 80.0 95-2 97.5 98.3 98.7 99.0 C. 100.0 96.2 83.4 71.7 33.4 20.0 4.8 2-5 1.7 1.3 1.0 D. 20.20 20.25 20.20 20.10 19.85 19.70 19.30 18.70 18.10 17.45 17.10 E. - - - 72-10 34.00 20.50 5.02 2.70 1-92 1-53 1.20 F. - - -_ 0.40 0.60 0.50 0.22 0.20 0.22 0.23 0.20 We believe that for practical purposes it will be found best simply to add the values shown in the tables under column F (which represent the influence of definite percentages of sucrose, expressed on the total sugars present) to the percentages of invert sugar, determined by direct titration.For this purpose, how- ever, it is necessary to know the percentage of sucrose, not calculated on the sample, but on the sugars (invert sugar and sucrose) in the sample. This can be determined either by the Clerget method or by the method of double titration before and after hydrolysis with hydrochloric acid. Since only the approximate percentage of sucrose is required in order to deduce the correction, the value calculated by the usual formula when the titration method is used is sufficiently accurate. This formula is as follows : 95(I’ - I) 100 ’ s= ~ in which S is the approximate percentage of sucrose, I is the apparent percentage of invert sugar-i.e., the direct titration value-and I’ is the percentage of invert sugar obtained by titrating the sample after complete hydrolysis.The appropriate value given in column F is subtracted from the value of I and added to the value of S, the respective results giving the corrected per- centages of invert sugar and of sucrose. In order to express these on the sample, S + I each of the values is multiplied by ----. To be exact, the value added to the 100 approximate percentage of sucrose, S, should be diminished by 5 per cent. ; but the accuracy of the method does not warrant this refinement, seeing that the corrections to be applied are values of comparatively small magnitude. The titrations recorded in this paper were practically all carried out by Messrs.George McLaren and R. C. Denington, to whom our best thanks are due.THE ANALYST. 171 DISCUSSION. Mr. CHAPMAN said that a good many years ago he was in the habit of using the volumetric process entirely, as being the best then in existence. In regard to the end-point, the accuracy with which a trained normal eye could determine the disappearance of colour without the aid of a chemical indicator was extraordinary ; but that, of couree, only applied to solutions which were colourless, or nearly so. During the past two years he had had considerable experience with the use of the ferrous thiocyanate indicator, and he should like to say how admirably it had worked in his hands, and how much it had contributed to making the volumetric process a more accurate and a more generally useful one.He entirely agreed with the authors as to the necessity of adding the sugar solution to the Fehling’s solution in small quantities at a time. Under ordinary circumstances it was not well to run in quantities of more than 4 or 5 C.C. at the commencement, and, of course, much smaller quantities towards the end of the titration. That the authors had been able to so increase the accuracy of the volumetric process as to be able to get results correct to within 1 part in 250 was a notable achievement, and one on which they were to be congratulated. For a good many years he (Mr. Chapman) had used the gravimetric process, and he had found no dificulty in obtaining duplicate weighings of oxide of copper agreeing within 1 milligram, but, of course, the difference might occasionally be a little greater.Some years ago he had made very numerous experiments as to the copper-reducing powers of invert sugar, dextrose, and maltose, for the conditions under which he was in the habit of working in his own laboratory, and he was accustomed to use his own numbers in place of those of Brown, Morris, and Millar, although there could, of course, be not the slightest doubt as to the high degree of accuracy which those chemists had reached. I n regard to the effect of concentration, his results had shown that the copper-reducing power of maltose was very much less affected than that of dextrose or of invert sugar, and that, in consequence, a factor could be used for the conversion of oxide of copper into maltose without introducing any serious inaccuracy. He had also made some experiments with lmulose, but at that time it was exceedingly difficult to obtain that substance in a state of sufficient purity, and so the experiments were not carried very far.In the estimation of invert sugar, the error due to the influence of cane-sugar was not usually very serious, although in the case of molasses and similar products it might be quite appreciable. It would, however, be very useful to have the accurate figures which the authors had given, and to know what the error really amounted to. He should like to hear how the lamdose used by the authors had been prepared and purified. Mr. W. T. BURGESS thought that the necessity was not sufficiently realised of seeing that small pipettes were always quite accurate and used in a, definite manner.He thought it very unlikely that if the same 10 C.C. pipette were used by three observers the respective quantities delivered would agree within 1 part in 300, or .03 C.C. Care would therefore be necessary in measuring the small quantity of Fehling’s solu- tion (10 c.c.), otherwise an error of 1 in 300 might be expected, apart from other experimental errors in the authors’ process.172 THE ANALYST, Mr. JULIAN L. BAKER said he was convinced of the great accuracy of which the volumetric process was now capable, and he felt able to rely entirely upon it, and to eliminate the gravimetric process. Years ago, when potassium ferrocyanide was the only indicator used, the volumetric process was capable of a certain degree of accuracy, provided the amount of reducing sugar measured was small; but the use of this indicator had the great disadvantage that the solution containing an excess of cupric salt had to be filtered through paper, and it had been pointed out by Dr.Divers that the results were apt to be erroneous, owing to absorption of the copper salt by the paper. With pure sugars, etc., giving clear solutions, he thought that, as Mr. Chapman had mentioned, an indicator was hardly necessary, but it was essential in dealing with dark sugar products like caramel, malt extracts, black beers, etc. H e asked the authors if they had investigated the influence of the time of boiling upon the results, because different people’s ideas of bringing to a boil varied somewhat.He was looking forward to studying the authors’ maltose curve, because in some recent work he had obtained very pure maltose-pure to the extent of crystallising from water-and had found its reducing power to be from 101 to 1014. Mr. J. H. Millar had obtained the figure 101, working with pure maltose. Mr. H. HULTON agreed with what had been said as to the necessity for running in the sugar solution in small quantities. He did not think that an indicator was necessary when titrating starch degradation products, because a very good indication of the end of the reaction was given by the characteristic frothing which took place, He thought that the dieculty with Iwulose which had been mentioned was due to the great susceptibilitg of ltwulose to decomposition by strong alkali, and that while part of the lamdose was reducing the copper, some of it was being decomposed by the excess of soda, and he should therefore expect that no amount of repetition would give concordant results.Mr. E. H. JEFFERS asked if the authors had made any comparison between the limits of error when ferrocyanide and ferrous thiocyanate respectively were used. He thought that really the only objection to the use of ferrocyanide was that most operators filtered rather a large quantity in order to get the reaction on a plate, but by the method recently suggested by Messrs. Watts and Tempany, of simply with- drawing a drop on a rod and placing it on a couple of sheets of filter-paper, it was possible to obtain the reaction in a similar way to that adopted by the present authors.Mr. LING, in reply, said that the sugars they had used in their experiments had all been highly purified, recrystallisation being continued until the specific rotatory powers (based on readings in 8 400 mm. tube) were practically constant. The publication of the ltievulose values was justified, not only because they were able by averaging these values with those obtained with dextrose to check the values obtained from the product of the inversion ” of sucrose, as they carried it out, but also because it was now usual to return the percentages of dextrose and lz?vulose separately in the analysis of commercial invert sugars, these latter sugars being sometimes adulterated with starch sugar (dextrose).Seeing that the ltlevulose used was of such a high degree of purity, he did not think much advantage would accrue from a repetition of the values obtained with that sugar. He agreed with Mr.HultonTHE ANALYST. 173 that, in all probability, the lesser accuracy of the values they had obtained with levulose as compared with the other sugars was to be ascribed to its ready de- composition under the influence of alkalies. With regard to the question of time, this was quite as constant with each individual worker in the volumetric process as it was in the gravimetric. The limit of accuracy of the two processes was discussed at length in the paper by Mr. Jones and himself. He had not made any comparison between the ferrocyanide and ferrous thiocyanate indicators recently, but whereas with the latter duplicate burette readings agreed within 0-1 c.c., when ferrocyanide was used it was difficult to get them closer than 0.5 C.C. Over twenty years ago he had used the method of applying the ferrocyanide indicator on a pad of filter-paper, but he did not think that it had any advantages over filtration. Mr. JONES agreed with Mr. Burgess that a pipette which delivered 10 C.C. of water would not deliver that quantity of Fehling’s solution, but a pipette could be chosen which did deliver 10 C.C. of Fehling’s solution ; or, more simply, any ordinary pipette might be marked and set aside for use in this work. Their own practice was to use a graduated pipette, sold to deliver 10 C.C. of water between the marks 0 and 10, and it was a matter of indifference to them whether it delivered 9.9 C.C. or any less quantity, as the difference between any two deliveries was exceedingly small, and the pipette used in standardising the solution was always used in analytical work with that solution.

ISSN:0003-2654    

DOI:10.1039/AN9083300167

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 173 LEAD IN CREAM OF TARTAR TARTARIC ACID AND CITRIC ACID. BY R. R. TATLOCK AND R. T. THOMSON. (Read at the Meeting April 1 1908.) SINCE the issue about a year since of Dr. MacFadden’s Report on “Lead and Arsenic in Tartaric Acid Citric Acid and ?ream of Tartar ” to the Local Government Board (ANALYST 1907 32 l89) the question as to the standard for lead in these articles and the best method of estimating it has been of considerable interest to Public Analysts. In dealing with the first of these questions no one can reasonably object to the first of Dr. MacFadden’s conclusions-namely ‘‘ In view of the uses to which tartaric and citric acids and cream of tartar are put recognised definitions of objectionable impurities are needed for application by manufacturers chemists and analysts and for use by importers and merchants selling these materials for food and drug pur-poses.” Nothing would appear to be fairer than this proposal but it is just here that dificulties arise as we must have a rational basison which to rest any standard that may be adopted.This may be arrived a t from a consideration of what can be obtained when purchased in the ordinary way or from a physiological standpoint. Taking cream of tartar first it would appear that Dr. MacFadden has proposed 0.002 per cent. as the highest allowable limit for lead because “ at a meeting held by certain mem 174 THE ANALYST. bars of the trade in 1904 at which several Public Analysts and others attended,” thi8 figure was decided upon. He further states that “ analysts generally have regard ” to this standard but the fact of the meeting referred to and of analysts having accepted the ‘‘ standard” fixed had not as far as we are aware penetrated to benighted Scotland.Now it is apparent that Dr. MacFadden has based his recom-mendation simply upon what is supposed to be obtainable in the ordinary way as he says this standard is corroborated by the analyses he made of seventeen samples of the commercial article showing from nil to 0.0033 per cent. of lead with an average of 0.0015 per cent. E e has thus adopted as his standard somewhat more than the average in the samples he has actually analysed which is surely not the most rational way of proceeding. Our experience of about one hundred samples of cream of tartar taken in various districts in Scotland is that the lead varies from 0.0005 to 0.041 per cent.with an average of fully 0.005 per cent. ; and if a standard is to be fixed in this fashion this one would be based on a much larger number of analyses and in that respect would be more reliable. But surely it would be much more satisfactory to fix a standard on the results of the evidence of experts on lead-poisoning such as was done in the case of arsenic-poisoning by the Commission appointed for that pur-pose. The best evidence on this question appears to show that one-tenth of a grain of lead can be taken daily by an adult without any deleterious effect so that if Dr. MacFadden’s standard is applied to cream of tartar 114 ounces of that article would require to be consumed daily and still the quantity of lead taken would not be harmful.In view of this and from the fact that cream oE tartar of the purity now demanded has not been sold and that no case of poisoning has been reported, it is surely reasonable that a rather higher percentage might be allowed as it is well known that a limit of 0.002 per cent. of lead is a fairly stringent one as regards the manufacturer. In any case a standard should not be fixed if the presence of lead is to be allowed at all without reference to the physiological factor. As far 8s tartaric acid is concerned the average percentage of Iead we have found is about the same a8 in cream of tartar the range in about fifty samples we have examined being from 0.0005 to 0.012 per cent. of lead. Our experience is quite against the usual opinion that cream of tartar is purer than tartaric acid as rggards lead as we have had samples of the former containing respectively 0.015 0.035 and 0,041 per cent.of lead while in the tartaric acid the lead has never exceeded 0.012 per cent. In some ten samples of citric acid examined by us the proportion of lead was practically the same as in tartaric acid the highest being 0.010 per cent. In this connection we may add that in no case when carefully tested have we found cream of tartar tartaric acid or citric acid quite free from lead and even a well-known German make of tartaric acid guaranteed to be lead-free contained 0.0015 per cent. of that metal. In view of the facts we have stated it is quite apparent that a standard for lead in these articles is urgently required but thiR should certainly be fixed on a rational basis.We now come to the consideration of the detection and estimation of lead in the three substances under discussion and little perhaps may be left to say after what has been written on this subject by Teed (ibid. 1892 17 142) when he introduce THE ANALYST. 175 the use of potassium cyanide the elaborate survey of the whole subject by Warington (JOUWZ. SOC. Chem. Ind. 1893 12 97 222) the excellent paper by Budden and Hardy (ANALYST 1894 19,169) and the interesting discussions on all these. There cannot be the slightest doubt that the colorimetric method with ammonium sulphide in an alkaline solution containing a little potassium cyanide is an excellent one but it is beset with difficulties which have partly been referred to in previous papers.Before dealing with these we may just describe shortly the method as employed by ourselves which consists in treating 10 grams of cream of tartar with 50 C.C. of water and 40 C.C. of 2N ammonia solution agitating till dissolved then making up to 100 C.C. with water mixing well and filtering through a dry filter For tartaric acid 10 grams with 81 C.C. of 2N ammonia solution and 9 C.C. water and for 10 grams of citric acid 85 C.C. of the ammonia solution and 5 C.C. of water are employed of course making up the solutions to 100 C.C. with water. In each of these cases the excess of ammonia will be equal to about 14 C.C. of the double normal solution and as we found by experiment 100 C.C. of any of these solutions will dissolve at least 2 grams of sulphate of lead there is no danger of lead remaining insoluble.To 50 C.C. of this filtrate there are now added 0.1 gram of potassium cyanide and 1 C.C. of a colourless or almost colourless strong solution of ammonium sulphide and the usual comparison then made with a standard solution of a lead salt. So far all seems simple and easy but certain difficulties arise some of which have been pointed out in former papers. We have not seen it noted before that ~ o m e specimens of cream of tartar give a brownish tint in the alkaline solution as prepared in the manner stated but as a rule it is similar to the tint given by sulphide of lead under the circumstances. In order to eliminate this error it is only necessary before adding ammonium sulphide to determine how much of the standard lead solution is required to produce this colour and to make allowance for it in the final result.The brownish colour referred to appears to be due to organic matter and it would certainly be advantageous to remove it but trials in this direction have so far been failures. It has been stated that the depth of colour given by equal quantities of lead in a water solution and a solution of a tartrate respectively may be quite different from each other and hence the necessity of using a standard tartrate solution in making comparisons for the purpose of estimating the proportion of lead. As far as our experience goes we are unable to corroborate this view as a general statement but the peculiarity may quite possibly occur under certain conditions.We find that if sufficient water with about 7 C.C. 2N ammonia solution 0.1 gram of potassium cyanide and the amount of standard lead solution required are mixed together before addition of ammonium sulphide a perfectly satisfactory standard solution is obtained. There are two necessary conditions however these being that the amount of lead present in 50 C.C. of the standard solution and of course also in the quantity of sample operated upon should not exceed one-fifth of a milligram and that no lead should be added to make up deficiency after the addition of ammonium sulphide but that a fresh standard should always be prepared. The only other point to consider is the effect of the presence of other metals on the determination of lead by the method in question.Of course we all accept th 176 THE ANALYST. general statement that copper tin and iron do not affect the determination; but we are not aware except in one instance what are the limitations to this as it is obvious that in the case of iron for instance where more or less coloured products (ferricyanide or ferrocyanide as the case may be) are formed there must be a limit beyond which the presence of iron must have an injurious effect. This is said by a correspondent ( ‘ I Plumbum ”) in the Pharmaceutical JozmznZ for February 22 1908, to be when the iron exceeds 50 parts per million; and this seems to be correct as from the results of our own tests we should say that if the iron either in the ferric or ferrous condition does not exceed one-fourth of a milligram in 50 C.C.of the solution operated upon the estimation of the lead may be relied upon ; otherwise the proportion of lead found may be on the high side. As regards copper and tin it was found that these up to 1 milligram in 50 C.C. of solution did not affect the result for lead but we have not tested beyond that; and it was also found that a mixture of 1 milligram of these metals and one-fourth of a milligram of iron had practically no effect. Observations extended to other metals showed that 1 milligram of mercury and nickel under the same conditions had no apparent influence. The only other metal we have examined in this connection is bismuth and we find that in every respect it is similar to lead and eo far we have not found any means of destroying its influence but the potassium iodide test is quite as delicate as that with ammonium sulphide.This can be applied by dissolving 5 grams of tartaric acid or citric acid in 50 C.C. water or 5 grams of cream of tartar with about 27 C.C. of normal hydrochloric acid and 23 C.C. of water then adding 1 gram of potassium iodide and filtering. When treated in this way even one-tenth of a milligram of bismuth produces a bright yellow colour and the proportion can be easily determined by a colorimetric method based on the addition of the requisite amount of standard bismuth nitrate solution to 5 grams of tartaric or citric acid. In order to make certain that any yellow colour is not due to liberated iodine the addition of solution of starch will disclose the presence of this as the double compound of bismuth and potassium iodide gives no reaction with starch.This concludes our investigation so far as we have gone but the question of the influence of iron in the estimation of lead certainly requires further examination as also does that of other metals. As regards tartar substitutes and baking powders containing phosphates and sulphate of lime our experiments are not far enough advanced. DISCUSSIOX. The CHAIRMAN (Mr. Bevan) said that the sugar and extractive matters present had a considerable influence on the colour produced by ammonium sulphide or sulphuretted hydrogen and he thought the President would probably agree with him that although in general it made no difference the use of a lead-free solution of as nearly as possible the same composition as the solution under examination was preferable to the use of plain water.Mr. A. E. PARKES remarked that Mr. J. Colwell and himself in some experiments on the detection of the metallic contamination of tartaric acid and cream of tartar, had found extract of logwood to be a very delicate reagent Although it did no THE ANALYST. 177 differentiate between the metals it gave positive results with quantities too small to be capable of detection by ammonium sulphide. Some pure samples of these substances which they had recrystallised themselves gave no reaction but the majority of commercial samples gave a blue colour with logwood although in many cases they gave no reaction with ammonium sulphide. Mr. C. A. HILL said that his experience during the last four or five years went to show that in unlimited quantity and at competitive prices cream of tartar could be obtained in which the proportion of lead was consistently less than 5 parts per million.That was the best grade and the analyses on which he based that statement would certainly represent many hundreds of tons. I n lower grades such as what was sold as 98 per cent. cream of tartar the proportion of lead might reach 20 and sometimes 25 parts per million ; but proportions like 40 parts per million which were constantly met with years ago had not come within his experience so frequently of late. In tartaric acid of English manufacture the quantity of lead would aertainly not exceed 10 parts per million or half the quantity suggested as a limit in Dr.MacFadden’s report and the foreign-manufactured article could also be obtained of about the same degree of purity. Citric acid was so very much purer that the question of lead contamination hardly ever arose. I t could be obtained contabing as little as 1 part per million which was about the limit of what could be determined with any certainty. Warington had shown very clearly the fallacy of comparing the colour produced in a tartrate or citrate solution containing lead with that produced in a solution of a lead salt in water and that was confirmed by his (the speaker’s) experience and that of other workers within the last four or five years. The coloration given by lead sulphide in a tartrate solution was not only deeper than that given in water but the tint was different being a clear brown while in water it was greyish; so that quite apart from the difference in depth there was the difficulty of comparing two colorations of different quality.Mr. CHAPMAN said that the question of the degree of purity which it was possible to attain in practice in respect of such materials as tartaric acid and cream of tartar was of great importance because it seemed to him that they should be guided not so much by physiological considerations as by a knowledge of the greatest purity that manufacturers could reach without an undue strain. Mr. Hill had just given them some important numbers indicating the degree of purity which manufacturers could observe in the course of ordinary trading and under competitive conditions and he (Mr.Chapman) thought that analysts should not be content with a purity appreciably less than that represented by those numbers. Some years ago maltsters had very freely expressed the opinion that it would be impossible to manufacture malt sufficiently free from arsenical contamina-tion to come within the limits recommended by the Royal Commission on Arsenical Poisoning; but as the result of care and attention it had been found to be quite possible to do this without the infliction of any great hardship or the imposition of any severe strain. Mr. E. HINKS said that within the past six months he had examined a number of samples of cream of tartar and tartaric acid obtained under the Sale of Food and Drugs Act from various parts of the South of England and had in no cas 178 THE ANALYST-found as much as 0.002 per cent.of lead3 Usually there was about 8 third of that quantity. Dr. DYER said it was probably well known that susceptibility to lead-poisoning was largely a matter of idiosyncrasy. In cases in which the water-supply of a whole town was contaminated with lead the majority of the people might be free from any noted symptoms of lead-poisoning while some would suffer acutely. An eminent toxicologist Dr. Luff had stated not long sgo‘in the witness-box that he had known marked symptoms of lead-poisoning to be induced by the daily consumption of 24 pints of drinking water containing as little as & grain of lead per gallon. That was probably the extreme of those cases which had been recorded.Articles like cream of tartar and tartaric acid were used in large quantities for making home-made lemonade and 80 forth and as it was practicable for manufacturers to reduce the lead to SO small a quantity as had been mentioned he certainly thought they should try to keep the standard of purity as high as possible. A great deal had already been done for when this matter was first actively brought forward a few years ago as much as a grain of lead per pound was not infrequently met with and he had had oases in whiuh there was considerably more than that. The proportion had steadily diminished until now it was exceptional to find anything much above the limit laid down in Dr. MacFadden’s report. In country districts it sometimes took 8 long time for materials of this kind to get from the manufacturer to the consumer and it seemed possible that a good many of such lead-contaminated samples as the President had referred to as having come within his experience might have been from remnants of old stocks such as would not be produced now that the matter had received the careful attention of the manufacturers.Mr. E. M. HAWHINS said that there recently came under his notice a sample of tartaric acid taken under the sale of Food and Drugs Act in ti country place which afforded valuable confirmation of the President’s observations regarding the elimination of the influence of copper. While the lead was considerably above the limit which had been suggested the sample also contained copper and after careful experiment he had found it was possible to estimate the lead accurately by the cyanide process substantially as the President had described in the presence of a considerable quantity of copper.The material from which the sample was drawn had been in stock 8 long time and a brass spoon had been used for it so that the presence of copper was not due to any fault in the manufacture but to the conditions of storage. The PRESIDENT in reply said that it was brought to their notice from time to time that Public Analysts had the power-whether they had the right or not he did not know-to evolve out of their inner consciousness standards of an ideal nature, which merely served to harass honest people in a small way of business who had no power to defend themselves and one of his objects had been to emphasiae his view that standards should not be established in that way or even on the recommendation of an official of a Government Department acting alone but only after careful consideration by a11 the various interests concerned and after evidence had been taken such as had to a limited extent been given during that discussion

ISSN:0003-2654    

DOI:10.1039/AN9083300173

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 179 THE ESTIMATION OF NITROGEN. Part 1.-The Nitrogen Factor for Casein. BY H. DROOP RICHMOND, F.I.C. THE object of this investigation was to ascertain whether the factor 6-37, used for the milk proteins, was applicable to both casein and albumin when the nitrogen determination was made by the Kjeldahl method. The starting-point was some observations made many years ago, that whilst preparations of lactalbumin gave results for nitrogen very closely agreeing with those required by the above factor--i.e., 15.7 per cent. N-several preparations of casein gave results seriously below this, the minimum being 14.2 per cent. N. I t was noticed that the more carefully the purification of the casein was carried out, the higher were the results, but the highest was but slightly over 15.0 per cent.I t was thought that this might indicate that Kjeldahl’s method did not give the whole of the nitrogen as ammonia, and a special investigation was made to test this ; as, however, it has been proved that this is not the case, it will not be necessary to give the experiments in full. The first series of experiments was made by estimating the nitrogen by the various modifications of the Kjeldahl method, using several reducing agents, but no difference in the Tesult was obtained. The second series consisted of estimations of the nitrogen by Dumas’ method, and by Kjeldahl’s method in an atmosphere of carbon dioxide. The gases evolved from the Kjeldahl estimation were passed over a layer of manganese dioxide, then over a long layer of heated cuprio oxide and in some cases a layer of lead chromate, and collected over caustic potash solution, the unabsorbed gas being measured and calculated as nitrogen. I t was observed that an appreciable amount of permanent gas was evolved quite early in the heating with strong sulphuric acid.The results were calculated for dry and ash-free casein : Per Cent. Per Cent. Mean. Nitrogen by Dumas .. . ... 16.26, 16.67, 16.71 ... ... 16.55 Nitrogen by Kjeldahl ... ... 15.26, 15.26 ... ... 15-26 Gas as nitrogen ... ... 1.20, 1.40 ... ... 1.30 The agreement of the sum of the Kjeldahl nitrogen and the gas evolved with the Dumas nitrogen appeared to show that nitrogen was evolved as gas, but on testing the gas it was found to burn with a blue flame. On heating 5 grams of casein with strong sulphuric acid in an atmosphere of carbon dioxide, 65-5 C.C.of gas were collected after absorbing the carbon dioxide, and of this 0-5 C.C. were absorbed by alkaline pyrogallol, and 63.0 C.C. by ammoniacal cuprous chloride; the residue was taken as nitrogen, as it did not explode with oxygen, and as it was four times the oxygen, it was evidently due to atmospheric air, which had not been removed from the apparatus. Carbon monoxide was also identified in the gas by the spectroscopic examination of blood treated therewith. I t is evident that no nitrogen is evolved as gas in the Kjeldahl method, and that180 THE ANALYST. the high result in the Dumas method was due to unburnt carbon monoxide. I con- clude that the Kjeldahl method is better and more reliable for the estimation of nitrogen in casein, and probably in all proteins, than the Dumas method.As the casein used had been extracted with ether, it was not previously thought necessary to look for fat as an impurity; but as a possible explanation of the low results, estimations of fat by the Gottlieb and Werner-Schmid methods were made, and in the specimen which gave the above results 1.9 per cent. of fat was found, and the nitrogen corrected for this impurity was 15.56 per cent. I t has been observed (Miller and Richmond, ANALYST, 1906, 31, 321) that milk proteins take up small quantities of aldehyde from ether ; by estimating the aldehyde figure of casein treated with ether, and comparing it with that of casein which has not been treated, it appears that a small correction should be made for this.The following is an analysis of a carefully purified sample of casein : Moisture ... ... ... ... 11.76 per cent. Fat ... ... ... ... ... 1-46 ,, Milk-sugar ... ... ... ... None Ash ... ... ... 1.75 per cent. Nitrogen ... ... ... ... 13.26 ,, Aldehyde condensed' '. ... ... 0.41 ,, Nitrogen corrected for impurities ... 15.67 ,, The experiments give a mean value of 15.65 per cent. nitrogen in casein, which I wish to acknowledge the assistance I have received from Mr. E. H. Miller in corresponds to the factor of 6.39. this investigation. Part 11. -Triazo Nitrogen. Forster and Fierz have described a series of compounds containing the triazo group (Trans. Chem. Soc., 1905, 87, 826 ; 1907, 91, 855, 1350, and 1942 ; 1908, 93, 72j, and they found that, although camphorylazoimide and the aromatic azoimides yielded two-thirds of the azidic nitrogen quantitatively as gas when treated with sulphuric acid, triazo-acetic ester gave abnormal results, only 16.3 per cent.instead of 21-7 per cent. being set free. The explosive nature of the aliphatic azoimides renders their combustion an inconvenient, and sometimes a dangerous, process, making it desirable to modify the treatment with sulphuric acid in such a way as will furnish quantitative results, and so dispense with the more usual method of estimating nitrogen. When the action of sulphuric acid on aromatic azoimi-des is normal an amine is produced, usually an amino-phenol. Moreover, Curtius and Darapsky (Journ. pr. Chern., 1901, ii., 63, 428) have shown that benzylazoimide is converted into imino- benzaldehyde, methylene aniline, and benzylamine. Forster and Fierz (Zoc.cit.) consider that with the aliphatic ketones an unstable ring is formed containing the three nitrogen atoms and the - CO group, and that this breaks down into an imine, though they obtained evidence that a portion of the nitrogen was split off as hydrazoic acid. Accordingly, it appeared to me possible that addition of form-THE ANALYST. 181 aldehyde, tending as it does to undergo condensation with amines and imino- compounds, would 80 regulate the action as to cause two-thirds of the azidic nitrogen to be removed in the elemental form, leaving the remainder to be estimated .by the Kjeldahl process. In the case of compounds of the type R - CH{N3),,, and especially it would be obviously necessary to have a reducing agent present, and formaldehyde would act thus.I t has been found that, while compounds of the types R - CH,N, and ‘‘CHN, Rl/ yield two-thirds of their nitrogen when shaken up in alcoholic solution with sulphuric acid and mercury, and more readily when addition of formaldehyde is made, bis-triazo-acetic ester, which is of the type RCH(N,),, gives but little more than one-third of its nitrogen with sulphuric acid, but yields readily two-thirds if forinaldehyde be added. I n this case evidence that the formaldehyde has acted as a reducing agent is afforded by the formation of formic acid, a portion of which yields carbon monoxide, small quantities of which were found in the gas.As mentioned above, Forster and Fierz found that only 16.3 per cent. of nitrogen was liberated by the action of sulphuric acid alone on triazo-acetic ester, while in the presence of alcohol and mercury I have succeeded in getting nearly 21 per cent. It ia curious that: the small difference in procedure should have led to this divergence. I am inclined to attribute it to the reducing action of the mercury; there is always a mercurous salt present in the sulphuric acid. Incidentally, I may mention that this forms a delicate test for traces of halogens. A precipitate is produced in the acid, whitish in the presence of chlorides and bromides, and green with some red coloration of the acid in the presence of iodides, and the presence of small quantities of halogen derivatives as impurities in some of the compounds experimented upon was at once shown by the formation of a precipitate.On suggesting this method to Dr. Forster, he kindly furnished me with specimens of a number of compounds. The method of analysis was to weigh about 0.1 to 0.2 gram into the cup of a Lunge nitrometer, and wash this in with several successive quantities of about 0.2 C.C. of alcohol; in many experiments 2 drops of 40 per cent. formaldehyde solution were added. Strong sulphuric acid was added little by little, and the nitrometer shaken between each addition. Brisk eEervescence set in after each addition till about 2 C.C. had been added, 10 C.C. being added in all. The nitrometer was shaken, and usually slightly warmed till all frothing ceased ; the apparatus was allowed to stand till the volume was constant, when it was read off, the level of the mercury in the side-tube being adjusted to the level of the iiiercury in the nitrometer.An allowance was made for the pressure of the column of acid (amounting to 6 mm. and 8.5 mm. in ths two nitroineters employed) based on calculation from the density and from actual measurement, the two values agreeing. The gas was taken as dry, and several observations were made of the volumes under greatly differing pressures. As the value of pv. was sensibly constant, it was proved182 THE ANALYST, that there was no appreciable vapour pressure from the acid mixture. The following is an example : (i.) 35.5 C.C. at 16.5' and 757 mm. 23.2.'. = 26.87 x 10" (ii.) 25.5 ,, ,, 16.5" ,, 1053 ,, ,, =26*85 (iii.) 60.3 ,, ,, 16.5" ,, 445 ,, ,, = 26.83 (iv.) 35.5 ,, ,, 16.5" ,, 757 ,, ,, =26*87 B vapour pressure of 2 nm. would certainly have been detected, and this would The acid was transferred to a flask, and the nitroineter washed out with About 2 grams of zinc-dust were added, and a determination have been within the limits of experimental error. 5 + 3 + 2 C.C.of acid. of the nitrogen by Kjeldahl's method made. The following results were obtained : Triazo-acetic ester, N,CH,COOC,H,- Without formaldehyde . . . 28.86 10.33 31.19 ... 20.73 10.20 30.93 Witd' formaldezyde . . . 20.81 10.65 31-46 Calculated., . ... ... 21-71 loss5 32.56 a-Triazo-propionic ester, C E , .CKN3.COOC2H5- Without formaldehyde . . . 19.00 10.21 29.21 ...18.96 10.36 29.32 Wit;' formaldecyde . , . 19.28 9.82 29.10 Calculated . . . ... ... 19.58 9.79 29.37 Second specimen, which contained a little CH, .CHBr.COOC2H5- hT as Gas. N as Aniiuonia. Total N. N as Gas. N as Ammonia. Total N. N as Gas. N as Ammonia. Without formaldehyde . . . 18.65 9.50 With formaldehyde . . . 18.83 9.59 P-Triazo-propionic eater, N,C EB,.CH,.COO C 2H,- N as Gas. N as Ammonia. Without formaldehyde . . . 18.78 9.65 With formaldehyde . . . 18.77 9.59 Bis-triaz9-ethane, N3CH2.CH2N2- N as Gas. N as Amuionia. With formaldehyde . . . 48.95 25.02 Calculated.. . ... ... 50.00 25.00 8 1 $ 7 ... 49.04 24-77 Bis- triaeo-ace tic ester, (N,),C R. COOC2E5--- With formaldehyde . . . 32-98 16.52 7 9 , I ... 32.81 16.50 Calculated.. . ... . I . 32.94 16.47 N a3 Gas. N as Ammonia.Total N. 28.15 28.42 Total N. 28.43 28.36 Total N. 73.97 73.81 75.00 Total N. 49-50 49.3 1 49.41 Batio. 2.02 2.03 1.95 2.00 Ratio. 1.87 1.83 1.965 2-00 Batio. 1.965 1-97 Elatio.. 1.95 1.96 Rati o . 1.96 1.98 2.00 Ratio. 2.00 1.99 2-00THE ANALYST. 183 These results were corrected for the presence of GO in the gas. The following results were obtained without correcting for the presence of CO ; and in the absence of formaldehyde : With formaldehvde . . . ... ~ l l ~ ~ ~ e ~ ~ d l q K as Aniinoniii. Total N .. 33.2 16.5 49.7 U $ 7 9 , ... ... ... 33.8 16.5 50.3 ... 33.7 - - ... Witll'out forGaldehyde . . . ... 19.5 16.S - - 9 7 7 1 .*. ... 19.5 16.5 The gas obtained without formaldehyde smelt strongly of hydrogen cyanide. By diluting the acid solution (2 c.c.) with water and distilling, a solution was obtained which on titration with silver nitrate and thiocyanate indicated 13.85 per cent.of nitrogen as HCN. I t is seen that where two triazo groups are attached to one carbon atom the use of formaldehyde is absolutely necessary, and the results must be corrected for carbon monoxide, Where only one triazo group occurs in combination with a carbon atom the result,s do not greatly differ with and without formaldehyde ; the use of formal- dehyde, however, seems to make the reaction more regular, and it is remarkable that in seven experiments where it was used the ratio of the two forms of nitrogen should only have varied from 1.95 to 1.98. The average of thesais 1.962, which indicates that 1.9 per cent.of the azidic nitrogen is not evolved as gas. I t would appear legitimate to multiply the readings of nitrogen as gas by 1.02, and, applying this correction, the results are- N,CH,.COOC.,H, 21.23 + 10.65 = 81-83 calculated 32.56 CH,.CRN,.C~OC,H, 19.65+ 9.82 = 29.47 ,, 29.37 N3CH,.CEL,.COOC,T1, 19.13 + 9.59 = 28.72 ,, 29.37 Forster and Fierz found by combustion 28.83 N,CH,.CH,N, . . . 49.93 -I- 25.02 = 74.95 ,, 75.00 . . . 7 , . . . 50.02 + 24-77 = 74.79 ,, 75-00 DISCUSSION. Dr. LEWKOWITSCH suggested that it might be possible by ~iieans of the chloramine reaction, which had lately been investigated by Cross, Bevan and Briggs (see p. 1%), to differentiate the proteins, or at any rate a portion of them, into different amino compounds. Dr. DYER said that the figures obtained by Mr.Richmond with the Dumas process seemed to represent nitrogen plus an unknown quantity of something which was not nitrogen. The experiments apparently showed that the Kjeldahl process was the only one that gave correct results. Mr. CHAPNAN said that these experiments seemed to afford another iudication of what, he thought, was now generally recognised-namely, that the Dumas process ought never to be taken as a standard process. I t had been shown that with some substances the process yielded more correct results when cuprous chloride was mixed with the substance, and this might possibly effect some improvement with casein. Nr. L. M. NASH asked how it was that, the casein having been thoroughly184 THE ANALYST. extracted with ether, something over 1 per cent.of fat was found in the extracted casein. Dr. RIDEAL said that MuIder (BerzeZizu Jahyesb., 1840, 19, 734) had pre- cipitated a number of proteins with chlorine, and determined the nitrogen in the precipitates, and in a paper which he (Dr. Rideal) and Mr. Stewart had read before the Society (ANALYST, 1897, 22, 228) the subject was also dealt with; while Allen and Searle (ibid., 1997, 22, 258), using bromine for precipitation, had obtained further results. Mr. RICHMOND, in reply, said that he had not made any experiments on the determination of the amino groups in casein by the chloramine reaction, but thought that this was a line of research which it would be worth while to follow up. He had, however, done what amounted to practically the same thing-namely, estimated the a-amino-acid groups by means of the aldehyde reaction, a little over 5 per cent. of the total nitrogen existing in this form in casein. He had also tried to estimate the total amino groups by treatment of the casein with nitrous acid, but this had not been very successful, because the casein, being insoluble, held back some of the gas. With regard to the nitrogen determinations, he had, perhaps, not made it sufficiently clear that he considered the discrepancies to be due, not to any fault in the Kjeldahl method, but to errors in the other methods. Owing to the comparative coarseness of its particles, the casein, even after extraction with ether, still contained some fat, which could be determined by either the Werner-Schmid or the Gottlieb method, the latter by preference. +?+**+I+&

ISSN:0003-2654    

DOI:10.1039/AN9083300179

出版商:RSC    

年代:1908

数据来源: RSC

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184 THE ANALYST. CARAPA OIL. BY J. LEWKOWITSCH, M.A., PH.D. THE information given in the literature on carapa oil is of a very indefinite nature. This is caused to a great extent by the conflict of opinions of the several botanists who have given descriptions of the carapa plant. Thus the Cnrapa guiaizensis, Sweet, or Cnrapa tozdozicozina, Guill. et Perr., has been described as a separate species, differing from the Cnrapn guinnensis, Aubl., which grows abundantly in Guiana, and especially in French Guiana. Several botanists consider the South American and West African species as identical ; especially so Oliver,‘:’ who declares the botanical differences, on the strength of which A. Jussieu, Richard, and others discriminated two species, as too unimportant to call for a subdivision into two species.The difference would seem to be based on the subdivision I of the carapa plants into (1) Pentamer@, with peduncled flowers and parts in fives, and (2) Tetrarnerd, with sessile flowers and parts in four. I n the former are included C. procera and C. szirinamensis, in the latter C. yzhiancnsas and C. moluccensis. In the Kew index Carapa guianensis and Cnrapa tozdozicozma are given as synonyms for Carapa procera, D. C., and according * ‘‘ Flora of Tropical West Africa,” vol. i., 1’. 336 ; cf. Seniler, “ Die tropische Agriknltur,” vol. ii., t Drabble, Qr~nrtcrly JoimnE, Liverpocl University, Institute of Comniercial Research in the 11. 151. Trol)jcs, vol. iii., NO. 6, p. 21.THE ANALYST. 185 to a communication received recently at the Imperial Institute from Iiew (and courteously given me by Professor W.R. Dunstan) on this subject, Carapa guianensis is Carapa procera. In Chateau's book ' I On Fats,"* the oil from Carapa gzcianeizsis is described as " carapa oil." I t is stated to differ from the oil obtained from C. toulozccouiza, which oil is described as " touloucouna oil." collate the numbers given by Heckel : i- This distinction has been emphasized by Heckel. I n the Shells ... ... ... ... ... Kernels ... ... ... ... ... Yield of oil from the total fruit ... Specific gravity at 15" C. ... ... Maumenb test ... ... ... ... Yield of fatty acids by '( saponification process " ... ... ... ... Solidifying-point of these acids ... Yield of fatty acids by '[ distillation process '' ... Solidifying-point of these acids ...Yield of solid fatty acids by [ [ saponi- fication process " ... ... ... Solidifying-point of these acids ... Yield of solid fatty acids by 'L distilla- tion process " ... ... Yield of glycerin ... ... ... ... ... ... Solidifying-point of these acids' ... Caral'a Seeds. 24 % 66 % Carapa Oil. 24.60 % 34O c. 94.9 % - 36.2" C. 86.3 % 39.2" C. 43 % 53" c. 49.28 % 49" c. 9.3 % ... ... ... ... ... ... ... I . . ... ... ... ... ... ... following tables I Touloucouna Setlds. 28.75 71.25 2 Tonloucouna Oil. 4346 % 0.932 30" C. 93-27 % 32.65" C. 83 % 39" c. 27.25 2 51' C. 48 % 48" C. 10.58 % These numbers evidently refer to experiments carried out on a manufacturing scale in candle works. The differences shown do not, however, in the author's opinion, establish a definite distinction between the two oils, and in view of the uncertainty attaching to the origin and to the original condition of the fats, and especially having regard to the conflict of opinions on the part of expert botanists, the author does not consider that there is sufficient justification for considering " carapa oil " and '' touloucouna oil " as two different individuals.Moreover, the name [' touloucouna" seems to be, if not a corruption of the word, at least of the same origin as that of taZloconah, a native name in British Guiana for the carapa tree,.; known there also as Last year Mr. Dawe, of the Forestry Department, sent home from Uganda a large consignment of nuts, which are declared by the authorities of Kew to be distinct from those of Carapa gzcianeizsis. The tree from which they are derived has been named Carapa grandipora, Sprague.crab " and '[ corap." * " Les Corps Gras indnstriels," Paris, p. 293, 1863. t " Les Grainev Graisses Nouvelles ou peu connues des Colonies Fransaises," pp. 141-153. +' Rlalonay, " Sketch of the Forestry of West Africa," p. 296. Paris, 1902.186 THE ANALYST. A considerable quantity of these nuts was sent to me by the Imperial Institute for examination. Oil from Carapa Grandi9ora. A large portion of the kernels were mouldy, and in several lots of nuts, amount- ing to about 10 pounds, the amounts of good kernels and shells were determined quantitatively with the following result : Good kernels, 36.3 to 42.1 per cent. ; bad kernels, 25 to 22-3 per cent; ; shells, 36.7 to 35.6 per cent. The good kernels yielded on extraction with ether 30.26 per cent.of oil. The large quantity at my disposal permitted the preparation of cold pressed oil, hot pressed oil, and cake on a, fairly large scale. For the preparation of the hot pressed oil good kernels were selected, comminuted in a. manner simulating the operations on a large scale, and expressed in the cold in a hydraulic press at a pressure of 150 atmospheres. The amount of cold pressed oil so obtained formed over 10 per cent. of the raw material. The cold pressed cakes were then broken up, comminuted, and heated to 150' F., when they were again expressed in the hot press at a pressure of 150 atmospheres. In this way a further quantity of hot pressed oil, amounting to almost double the quantity obtained by cold expression, was recovered.Quantitative recovery of the oil was, of course, out of the question, and the cakes finally obtained, contained much more oil than would be left in a commercial oil cake. The cold pressed oil, as also the hot pressed oil, were examined side by side, with the result set out below, The colour of the cold pressed oil is almost white, with a tinge of pale yellow. A t the ordinary temperature it solidifies. The hot pressed oil is much darker in colour, and remains solid at the ordinary temperature. The following characteristics were ascertained : Cold Pressed Oil. Specific gravity at 40" C. (water at Specific gravity'at 15.5' C. (water at ... 40= 1) ... 0.9171 15.5=1) ... ... ... ... 0.9261 Solidify ing.-point ...... . . , 8" C. Melting-point . , . ... ... ... 15-23' C. Saponification value ... ... ... 198-1 Iodine value ... ... ... ... 83.7 Reichert -Meissl value ... ... ... 3.75 Unsaponifiable matter . . . ... ... 3.75 Hot Pressed Oil. ... 0.9215 ... 0-9306 ... 10' c. ... 20-30' C. ... 201.8 ... 72.6 ... 3.83 ... 1-59 % Chnrncteristics of the Insoluble Fatty Acids. Cold l'ressed Hot Pressed Oil. Oil. Fatty acids + unsaponifiable . , . ... 94.03 % ... 92.93 % Solidifying-point (Titer test) ... ... 34.9O c. ... 38-9" C. Mean molecular weight of the fatty acids 277.3 ... 277.1 Neutralisation value ... ... ... 202.3 ... 202.4THE ANALYST. 187 The insoluble fatty acids consisted of : Cold Pressed Hot Pressed Oil. Oil. soluble in ether) ... ... 72.82 % ...64.62 % insoluble in ether) ... ... ... 26.47 % ... 34-93 % " Liquid " acids (lead salts of which are '' Solid " acids (lead salts of which are Iodine value of liquid fatty acids . . . 94-74 . . . 94-71 Iodine value of solid fatty acids ... 8.8 ... 9.97 The solid acids from the cold pressed and hot oils yielded respectively 3-15 per cent. and 6.6 per cent. of '' stearic acid " of the melting-point 65.6" C. The oils, as also the cake, have an intensely bitter taste, which seems to be characteristic of all the oils derived from the seeds of the Carapa family. ~ommercial Value of the Kernels aitd Oil.-The oil would be worth about g24 t o 625 per ton. The value of the kernels would depend on what use can be made of the cakes. If the bitter principle in the cakes precludes an outlet in this direction, then the cakes could only be used as manure; in that case the value of a ton of cake would be about 62.Assuming that the cake is only usable as manure, the value of the kernels would be 65 to 66 per ton. The analytical determinations were made by Dr. H. Pick and Mr. G. Warburton, to whom my thanks are due. DTSCUSSION. Mr. L. M. NASH said that the figures yielded by an authentic sample of carapa oil from the seeds themselves would be of great interest to those who in the future might have to examine this oil; for the figures of Deering and Hannau, which were quoted in Dr. Lewkowitsch's book, were so divergent as to render them useless for deciding whether a sample was genuine. I n particular, the figures given for the melting-point of the mixed fatty acids were as widely apart as 38.9" C. and 564" C., and the melting-point of the oil itself was actually given as being 5" C.lower than the solidifying-point. I n the case of Chinese vegetable tallow, there was also a wide divergence between the recorded melting-points (39" to 53.2" C.), due to the fact that the fat surrounding the seeds was more or less contaminated with the oil expressed from the seeds themselves ; and he would like to know whether the variations in the case of carapa oil might be similarly brought about. Dr. LEWKOWITSCH said that, although he had quoted the figures to which Mr. Nash had referred, he took no responsibility for them. The variations in the recorded melting-points could not be accounted for, as in the case of Chinese vegetable tallow, for the carapa oil was obtained from the kernel of the nut only. He might add that it seemed well to put on record investigations such as this, not merely for the sake of any immediate interest they might have, but in case they might lead to more valuable results in some other direction, as happened, for instance, in Power's examination of the seeds of Taraktogenos Kurzii, which ultimately led to the discovery of a new series of optically active fatty acids. NoTE,-After the paper had been read the cold pressed oil was examined for optical activity. It was found that the substance rotated the polarised light 2" 4' to the left in a 100 mm. tube.

ISSN:0003-2654    

DOI:10.1039/AN9083300184

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

188 THE ANALYST. ABSTRACTS OF PAPERS PUBLISHED IN OTHER JOURNALS. FOODS AND DRUGS ANALYSIS. Estimation of Alcohol in Concentrated Nitrous Ether. W. A. Pearson. (dmcr. Jozwn. Pharm., 1908, 80, 101-105.)-Twenty to 35 grams of the preparation are rapidly weighed into a 200 C.C. flask containing ice-cold water, and the flask immediately connected with an upright spiral condenser, into the top of which is poured ice-cold water. If the lower opening be quite small, a spiral column of ice- water will be held in the condenser by the pressure developed by the volatilising nitrous ether. The ethyl nitrite evaporates at the ordinary temperature in about three days under these conditions. An alternative form of apparatus is one in which the vapours from the flask are made to pass through a series of five small wash- bottles contaihing ice-cold water.When volatilisation of the nitrite is complete, the solution in the condenser or wash-bottles is mixed with the liquid in the flask, and diluted to such volume that 20 C.C. contain about 0.1 to 0-3 gram of alcohol. The alcohol in 20 C.C. of solution is then determined by the method of DuprB, which consists in oxidising the alcohol to acetic acid by chromic acid and distilling the acetic acid from the liquid after destroying the excess of chromic acid with metallic zinc. The usual corrections for traces of sulphuric acid carried over in the distillation, and for any aldehyde or unvolatilised ethyl nitrite in the liquid before oxidation, should be made. A, R. T. Simple Method for the Estimation of Alcohol in Distillery Wash by Means of the Zeiss Immersion Refractometer.B. Wagner, F. Schultze, and J. Rub. (Chem. Zeit., 1908, 32, 297-298.)-The method consists in determining the refractive index on 5 or 10 C.C. of the filtered wash, and also determining the refractive index of 20 C.C. of the same solution after evaporating to 10 C.C. to expel the alcohol, and making up to 20 C.C. with distilled water. The difference of the two result8 is added to the value for the refractive index of water at the temperature used, the percentage of alcohol present being found by reference to II table contained in the original paper. For accurate work a correction amounting to 0.3 to 0.4 per cent. must be made to allow for the presence of insoluble matter (yeast) in the wash.A. G. L. Detection of Butter-Fat, Cocoanut Oil and Palm Oil in Cacao Butter. F. Strube. (Zeit. ofentl. Chem., 1508, 14, 67-70.)-The method employed was originally proposed by R. Cohn, and is based on the fact that the soap formed on saponifying cacao butter is quite insoluble in sodium chloride solution, whilst the soap obtained from cocoanut oil, etc., cannot be salted out completely from its aqueous solution, The method is applicable to the testing of the fat obtained from chocolates, etc. About 2.5 grams of the fat are saponified by heating withTHE ANALYST. 189 alcoholic potassium hydroxide solution, and the alcohol is evaporated on the water-bath. The residue of soap is dissolved in 55 C.C. of hot water, and, when the solution is cold, 50 C.C. of saturated sodium chloride solution are added.After the lapse of fifteen minutes, during which time the mixture is stirred frequently, the whole is poured on a filter, and to 60 C.C. of the filtrate a further quantity of 50 C.C. of the sodium chloride solution is added. I n the case of pure cacao butter the solution remains clear or exhibits only a faint turbidity ; the fat from (‘ milk chocolate ” also yields a clear solution, whilst cocoanut oil and palm oil give more or less heavy precipitates. If, after a short time, the solutions be again filtered and the filtrate acidified‘ with hydrochloric acid, the solution remains quite clear should the fat be cacao butter or the same mixed with butter-fat, whilst with cocoa- nut oil and palm oil a further turbidity is produced.The solution has also the characteristic odour of cocoanut oil fatty acids. The presence of butter-fat may be detected by the odour of butyric acid when the filtrate is acidified. I t is mentioned that the fat obtained from pressed and alkalised cocoas has the same melting-point and iodine value as pure cacao butter, showing that the treatment does not alter the composition of the fat, whether the alkali used be ammonia, potassium carbonate, or both. w. P. s. Estimation of Cocoanut Oil in Butter. G. R. Thompson and A. R. Tankard. (Chem. News, 1908, 97, 146.)-The authors have submitted the process described by T. R. Hodgson (ANALYST, 1908,49) to a critical examination, and find that the method is quite valueless for the estimation of cocoanut oil in butter.This conclusion is in agreement with that of Ross and Race (ibid., 1908, 122). The figures obtained in the experiments failed to differentiate butter from butter-substitutes or cocoanut oil. In the absence of any fatty acids, the sulphuric acid employed was found to have a, considerable action on the permanganate solution. w. P. s. Estimation of Mustard Oil. M. Kuntze. (A~chiv. Pharm., 1908, 246, 58-6Y.)--The following conditions are given for the volumetric estimation of mustard oil in alcoholic solutions of the same : Five C.C. of the tincture, containing about 2 per cent. of the oil, are placed in a 100 C.C. flask, 10 C.C. of ammonia and 50 C.C. of .& silver nitrate solution are added, the flask is attached to a reflux condenser, and its contents heated for one hour by means of a water-bath, which is kept boiling gently.After cooling, thc mixture is diluted with water to a volume of 100 C.C. and filtered. Fifty C.C. of the clear filtrate are then acidified with nitric acid, 1 C.C. of animonium ferric sulphate is added, and the excess of silver nitrate is titrated back with ;k ammonium thiocyanate solution. The author finds that a portion of the mustard oil is converted into allyloxythiourethane if an alcoholic solution of the oil be kept for a long time. This change may account for the untrustworthy results sometimes obtained on the analysis of old samples of the tincture. w. P. s. A New Vegetable Oil. P. Buttenberg. (Zeit. Untewich. Nahi.. Geizzissm., 1908, 15, 334-338.)-The author has recently examined an oil said to be obtained190 THE ANALYST.from the seeds of a Chinese plant; no particulars of the seeds are given, except that they are stated to resemble linseed. The oil had the following chemical and physical constants : Refraction at 40" C. ... ... ... ... ... 47.0 Acid value ... ... ... ... ... 9.4 Reichert-Meissl value.. . ... ... ... ... 34.8 Polenske value ... ... ... ... ... 0.5 Saponification value ... ... ... ... ... 234.7 Iodine value ... ... ... ... ... ... 64-6 Uneaponifiable matters ... ... ... . . . . 0.38 per cent. ... The oil gave a feeble reaction for sesame oil, but no reaction for cotton oil. Phytosterol acetate, melting at 180" C., was obtained from the unsaponifiable matters present in the oil. This melting-point is considerably higher than that of pure phytosterol acetate, and indicates the presence of dihydrophytosterol (ANALYST, 1907, 32, 424).w. P. s. Composition of Oil of Tarragon. M. Daufresne. (Bull. SOC. Chim., 1908, [iv. J 4, 330-335.)-0iI of tarragon (drtemisia draczmczdiu), which is largely used for flavouring condiments, consists of from 60 to 75 per cent. of estragol, 15 to 20 per cent. of tarpenes, and 0.5 to 0.6 of 23-methoxycinnamic aldehyde. Anethol is not present. The author has separated the terpenes into various portions, from which he has isolated an unsaturated substance analogous to myrcene and ocimene, and probably identical with the latter, and a cyclic hydrocarbon having dextro-rotary properties and closely resembling phellandrene. Two samples of the oil gave the following figures on examination : Specific gravity at 15" C.... ... ... Refractive index ,, ,, ... . . . Rotation at 20" C. ... Distilling under 1 4 mm. pressure at: 70" to 90" C. (Terpenes) ... ... 90" to 110' ,, (Estragol) .. ... 110" t o 160" ,, ... ... 160' to 180' ,, (Aldehydes) ... ... Residue, by difference ... .. ... ... 9 , ... ... French Oil. 0.949 1.517 + 7.8" German Oil. 0.945 1.5165 + 7.24" 17.6 grains 77.0 ,, 0.8 gram 1.2 grams 3.4 ,, w. P. s. Analysis of Oil of Lavender. P. Jeancard and C. Satie. (Bull. SOC. Chim., 1908, [iv.] 4,155-159.)-0f late years, owing to the increase in its price, there has been a hndency to adulterate oil of lavender, and the authors give certain limits within which, in their opinion, the chemical and physical'constants of oil of lavender ought to fall.The chief of these limits are : Specific gravity at 15" C., 0.880 to 0.890 ; rotation, - 6' to - 10" ; saponification value after acetylation, over 160. The figuresTHE ANALYST. 6.5 per Cent. Alcohol. 191 Before Acetylstion. are arrived at after the examination of a number of pure oils of lavender, the results of which analyses are given in the following table : LAVENDER FROM UPPER ALPS TO SUMMITS OF LOWER ALPS. -8.4" to t o - 9 " --6'to - 8.4" - i.1" to - 9.3" Yew. 1.7 2 t o 2.1 1.9 1905, 3 samples. 1906, 2 sninples. 1907, 4 samples. 2.6 t o 2.5 2.2 t o 2'6 3.0 t o 3'9 1906, 5 samples. 1906, 2 samples. 1907, 3 samples. 33.1 t o 65'1 65'1 t o 72'8 62.3 t o 8t.i Specific Qravity. 0.8854 tc 0 * 89 00 0.5872 t c 0.8580 0.8Si5ti to 0*5000 0.8828 to 0'8848 0.8836 t o 0.8848 0'8840 t o 0.8870 Rotation.- 7.10" LO -. 6.1" t o - 6.4" -;9 t o -- 8.3' - .L - 4 3olubility in Parts of- Saponification Value- 0 per Cent. Alcohol. 2 t o 2.7 2-4 to 2.5 2.3 t o 2.6 4.6 to 20 5.1 t o 20 20 91.7 t o 1 23 '9 100.1 t o 111 94 5 t o 131.6 I After icetyliition. 171 '5 to 179.9 166'6 t o 172.8 1;5 t o 194.5 16.5'9 t o 1 72.2 164-4 t o 167.2 170.9 to 188.3 Estcrs. 32 09 t o 43.36 35-05 to 38'85 33 07 to 46-06 20.33 to 22-79 25'46 t o 22.79 21'81 t o 29.64 The saponification value after acetylation is of importance, as it is a measure of the alcohols present in the oil. Adulteration with oil of spike-lavender increases the specific gravity and diminishes the saponification value, that of oil of spike-lavender Detection of Bilberry Juice in Red Wines.W. Plahl. (Zeit. Unterszcch. Nahr. Genussm., 1908, 15, 262-269.)-The reaction for bilberry juice, described previously (ANALYST, 1907, 32, 92), may be applied to the detection of this juice in completely fermented red wines. Fifty C.C. of the wine are rendered feebly alkaline in reaction by the addition of sodium hydroxide solution, and evaporated to a volume of about 25 C.C. After diluting to the original volume, the colouring matters of the wine are precipitated by the addition of lead acetate, and the mixture is filtered. A portion of the clear filtrate is treated with sodium sulphate, the lead sulphate is filtered off, the filtrate is acidified with hydrochloric acid, and heated on a, boiling water-bath. The blue coloration is obtained if the wine contains not less than 2 per cent. of bilberry juice. In some cases the colouring matters are not completely precipitated by lead acetate, and a faint red coloration may be produced on adding the hydrochloric aoid; this red coloration, however, appears at once (while the solution is cold), and the blue coloration, due to the bilberry juice, becomes visible being below 100. (See also ANALYST, 1900, 25, 297.) w. P. s. only when the solution has been heated for a little time. w. P. s.

ISSN:0003-2654    

DOI:10.1039/AN9083300188

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 191 BACTERIOLOGICAL, PHYSIOLOGICAL, ETC. Formation of Aldehydic or Ketonic Substances during Acetic Fermenta- tion, K. Farnsteiner. (Zeit. UnterszLch. Nuhr. Geizussm., 1908, 15, 321-326.)--All liquids which have undergone more or less complete acetic fermentation contain a192 THE ANALYST. neutral, volatile substance which reduces Fehling's solution. The copper reduction may in certain cases cause an apparent increase in the sugar percentage of 0.75 per cent., but the amount of the substance produced during the fermentation varies con- siderably, and bears no relation to the amounts of sugar, acetic acid, etc., present. The estimation of reducing sugars in vinegars and similar products should, therefore, be carried out on the partially evaporated sample. In its behaviour towards Fehling's solution and sulphurous acid the substance resembles acetol, which Kling (Compt.Rend., 1901, 133, 231) has shown to be the product of the action of Mycoderma aceti on glycol. I t differs from acetol in that its osazone melts at 243" C., whilst acetol osazone melts at 145" C. Besides the osazone, an oily substance is obtained when a solution of the substance is treated with phenylhydrazine. w. P. s. Changes in the Composition of the Body-Fat of Rabbits when the Animals are Fed or Inoculated with Cotton-seed Oil. K. Lendrieh. (Zeit. Untersuch. Nahr. Genussm., 1908, 15, 326-334.)-A number of experiments were carried out, in which five rabbits were fed with food containing cotton-seed meal, four with food mixed with cotton-seed oil, and five were inoculated every eight days with cotton-seed oil.Two rabbits were fed on ordinary food and served as a control. The experiments extended over a, period of from 21 to 402 days; in some cases the animals received ordinary food after the experimental period. The results of the examination of the fats'obtained from the rabbits show that continuous feeding with substances containing cotton-seed oil, although the daily quantities taken be small, has a retarding action on the deposition of the fat in the animal. The glycerides of the oil are deposited, and plainly alter the composition of the body-fat. After-feeding with other foods causes the gradual disappearance of the constituent which gives the reaction with Halphen's test, but the glycerides of the cotton-seed oil appear to remain for some time in the body-fat.Phytosterol was not detected with certainty in t,he fat of the animals fed with cotton-seed oil. When the rabbits were inoculated with the oil, the latter was absorbed rapidly, the presence of both the cotton-seed oil glycerides and phytosterol being detected in the body-fat. The latter also gave reactions with Halphen's test. w. P. s. The Cause of Poisoning by Arsenical Wall-Papers. B. Neppe. (Scienxa Pratica, 1908, 1, 82-84.)-1t has been found by Gosio that cases of poisoning by arsenical wall-papers are to be attributed, not, as commonly believed, to the dry dust given off by the paper, but to a volatile organic arsenic compound produced by the action of certain mould-fungi in the presence of carbohydrates (the paste by which the paper is attached to the wall).This action is strictly specific, and has only been found to be possessed by the following mould-fungi, arranged in the order of decreasing activity ; Penicilliuna brevicaule, Aspergillus clavatus, A . fumigatus, A . glaucus, A . virens, A . candidus, and Mwor mucedo. A certain degree of moisture is required, and it is stated that there is no risk of poisoning from an absolutely dry wall-paper. The optimum temperature for the action of the mould-fungi is about 25" C., and the process appears to be a direct vital phenomenon, and not due toTHE ANALYST. 193 diastatic action, Above a certain proportion of arsenic the mould-fungi themselves are poisoned, but they can gradually be rendered immune to larger quantities.The volatile organic compound was identified as diethyl arsine, H A ( C,H,),. When passed into a solution containing 8 to 12 per cent. of mercuric chloride and 20 per cent. of hydrochloric acid, it yielded the compound : /C&, + HgC4 H'As\C,H, + HgC1,. C. A. M. Iron Contents of Fats, Lipoids, and Waxes. W. Glikin. (Bey. dezbt. Chem Ges., 1908, 41, 910-915.)-Bone-rnarrow, purified by dissolving in ether and shaking with dilute acid, contains small quantities of iron. The iron contents of the fat are highest at the time of birth of the animal, and decrease from then onwards. Iron has been detected and estimated in fats other than bone fats, also in vegetable fats and various waxes. The iron exists in combination with the lecithin and cholesterol components of the fats, and purified samples of lecithin have shown as much as 0.5 per cent.of iron ; purified cholesterol may contain 0.06 per cent. In many cases the quantity of iron in the various fats was in constant proportion to the quantity of phosphoric acid in the ratio of Fe,O, to 3P,O,. J. F. B. Studies on Melanogenesis : The Action of Tyrosinase on Substances Similar to Tyrosine. G. Bertrand. (BzLZZ. SOC. Chim., 1908 [iv.], 4,335-343J-It is known that in the phenomenon of melanism-that is, the production of black pigment in vegetable or animal tissues-the oxidising enzyme, tyrosinase, plays an essential part. The blackening of the sugar in beetroots and in dahlia tubers, the coloration of brown bread, etc., ia due to this ferment, and in many cases the chromogen has been separated and identified. The results of experiments are now recorded, showing that tyrosinase has an oxidising effect on other substances than tyrosine, For instance, p-oxyphenylethylamine, p-oxyphenylamine, p-oxyphenyl- propionic acid, p-oxyphenyl-acetic acid, p-oxyphenyl-benzoic acid, p-creBo1, and phenol, are acted on by tyrosinase, the colorations obtained ranging from yellow to black. The dipeptide, glycyltyrosine, is readily oxidised in the presence of tyrosinase, the colour produced being red. On the contrary, phenylalanine, phenylethylamine, phenylaminoacetic acid, phenylacetic acid, alanine, glycocol, etc., do not give colorations when acted on by the ferment. w. P. s.

ISSN:0003-2654    

DOI:10.1039/AN9083300191

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 193 ORGANIC ANALYSIS. Further Notes on the Simplified Method of Ultimate Combustion Analysis. M. Dennstedt. (Bel-. deut. Chem. Ges., 1908, 41, 600-604.)-The author gives a minute description of the manner in which his improved combustion apparatus should be worked when dealing with any substance of unknown properties. This general method is not so rapid as the special methods applied to known substances, but it is often necessary to use it. When the substance in the insertion tube has been placed in the combustion tube, the stream of oxygen is adjusted, and the194 THE ANALYST. oombustion flame is gradually advanced under the contact material until the back portion of the platinum next to the insertion tube begins to glow. The roof of the furnace is placed so that it covers not more than 1 cm.of the insertion tube. The volatilisation flame is then turned up as far behind the substance in the boat as possible ; only very volatile substances are so far affected, most substances remain unchanged. When the contact material is glowing brightly, the volatilising flame is advanced about 1 cm. every three or four minutes, until the substance melts or deoomposes; it is then allowed to remain stationary for fifteen minutes, provided signs of combustion are visible. If not, the combustion flame, with the cover, is advanced 1 or 2 mm. at a time towards the boat, until combustion begins. When combustion slackens down the flame is advanced a little more, until the substance is either volatilised or oarbonised. The adjustment of the combustion flame and cover must be such that the platinum in front of the insertion tube is maintained at a bright red heat.The volatilising flame is only brought further forward when no more combustion can be obtained with the combustion flame. Finally the cover is placed over the volatilising flame, and the stream of oxygen is increased in order to complete the combustion of the carbon. The calcium chloride used for absorbing the water of combustion should be gently ignited before filling the absorption tubes, and the latter should then be saturated with carbon dioxide. The soda-lime used for absorbing the carbon dioxide of combustion may often be too dry for its purpose. When very high temperatures are necessary for the combustion, the fusion of the end of the insertion tube to the walls of the combustion tube may be prevented by winding a few turns of platinum wire round the former.In the determination of sulphur care must be taken to wash out not only the insertion and combustion tubes, but also the boat after the combustion, since small quantities of sulphuric acid are retained by them. The boat should also be extracted with hydro- chloric acid before commencing an estimation of sulphur. (Cf. ANALYST, 1908,146.) J. F. B. New Volumetric Method for the Estimation of Albumin by Phospho- Tungstic Acid. Tsuchiya. (Zentralbl. inn. Med., 1908, 29, 105 ; through Chenz. Zeit. Rep., 1908, 32, 149.)-The reagent used consists of alcohol (96 per cent.) containing 1.5 per cent. of phospho-tungstic acid and 5 per cent.of concentrated hydrochloric acid. I t is stated to give no precipitate with normalurine, to give more accurate results than Esbach’s reagent, to give approximately correct results even with large quantities of albumin, and to give a precipitate containing approximately the same percentage of nitrogen 8s that contained in the albumin present in urine. A. G. L. The Quantitative Conversion of Aromatic Hydrazines into Diazonium Salts. F. D. Chattaway. (Proc. Chem. SOC., 1908, 24, 74-75.)-AAll primary aromatic hydrazines can be quantitatively converted into the corresponding diazonium salts either by chlorine or by bromine. If either halogen be allowed to act at a low temperature on the hydrazine dissolved in alcohol, the diazonium salt separates out in a pure state.Unless, however, the solid salt is required, theTHE ANALYST, 195 operation can be most easily carried out by dissolving the hydrazine in glacial acetic acid, cooling the solution to about -15" C. by the addition of crushed ice, and either passing in a rapid stream of chlorine or adding the calculated quantity of bromine dissolved in acetio acid and similarly cooled by ice. The formation of the diazonium salt is without doubt of two atoms of hydrogen in the hydrazino group by elimination of halogen acid, thus : C8H, .N.H C,H,.N.CI H.N.Cl -3 I -+ I H.N.H effected. by a substitution halogen, followed by the C,H,.N.CI Ill N As in other cases where hydrogen attached to nitrogen is replaced by halogen, an additive product is probably first formed, in this instance by the addition of four halogen atoms, each nitrogen atom becoming quinquevalent ; the elimination of halogen acid then gives rise to the diazonium salt, which, being stable under the conditions of the experiment, can be isolated.Determination of Benzene in Illuminating Gas. L. M. Dennis and E. S. Mecarthy. (Jozirn. Amer. Chem. Soc., 1908, 30, 233-247.)-The ammoniacal nickel nitrate reagent proposed by Dennis and O'Neill was found to be inefficient as an absorbent of benzene, except in those cases where the gas also contained cyanogen, and this led to the preparation of ammoniacal nickel cyanide. This reagent quantitatively removes benzene from its admixture with air, and completely removes it from coal-gas in two minutes, while it does not absorb ethylene or other constituent of coal-gas, with the exception of those gases soluble in caustic potash.These should, of course, be first removed before treating with the nickel cyanide reagent. The reagent, which is capable of absorbing four times its volume of benzene, is prepared by adding 25 grams of potassium cyanide, dissolved in 40 C.C. of water, to 50 grams of cryatallised nickel sulphate, dissolved in 75 C.C. of water; 125 C.C. of ammonia (specific gravity 0.910) is then added to the mixture, which is shaken until the nickel cyanide is dissolved, and then cooled to 0" C. After twenty minutes the separated crystals of potassium sulphate are removed, and 18 grams of citric acid, dissolved in 10 C.C. of water, added to the clear solution. After ten minutes at 0" C.the greenish-blue supernatant liquid is decanted, and shaken in a Hempel gas pipette with 2 drops of liquid benzene for two minutes. This addition of benzene is advisable, since it was found that the freshly prepared reagent does not absorb well until it has been used a few times. The absorptions should be carried out in the Hempel pipette used for treating heavy hydrocarbons with fuming sulphuric acid, but it is better to have the upper bulb, which is filled with the broken glass, of a diameter of 4.6 cm. The gas to be examined should be repeatedly passed into this pipette containing the reagent, and back again, for two minutes, when the ammonia vapour left in the residual gas is absorbed by similar treatment with 5 per cent. sulphuric acid. The insoluble compound formed in the reaction, Ni(CN),.NH,.C,H,, should be filtered out after the reagent has been in use for some time, to prevent clogging of the pipette.The authors state that Morton's method for the estimation of benzene by196 THE ANALYST. means of strong sulphuric acid (ANALYST, 1907, 32, 61) gives inaccurate results, frequently failing to completely remove benzene, while absorbing a variable but considerable amount of ethylene. A. R. T. The Estimation of Phenols in Gas Liquors. F. W. Skirrow. (Jouriz. Gaslight, 1908, 100, 357-360.)-Cf. ANALYST, 1908, 134. For the colorimetric estimation of phenol in the gas itself, 50 to 60 litres of the sample are filtered through cotton-wool to remove tar-fog, and passed through two flasks containing 500 C.C. of 20 per cent.sodium hydroxide solution. The liquid in the flasks (after removal of cyanogen as iron ferrocyanide) is titrated with iodine and thiosulphate, and diluted until the red colour of the tri-iodophenol is only just visible, the solution then containing 0.00025 per cent. of phenol. The tar-acids in gas liquors were separated into (a) phenol, ( b ) cresols and crystal drainings, and (c) residues of high boiling-point. The original tar contains more cresol than phenol, but in the washing out with arumoniacal liquor, more of the phenol is dissolved. The presence of homologues of phenol introduces an error in the estimation of the phenol, the results being about 5 per cent. too low. Deter- minations of the oxygen absorption by means of permanganate, as in the method used in sewage works analyses, showed that 1 gram of phenol absorbed 1,401 grams of oxygen, 1 gram of cresol 1,245 grams of oxygen, and 1 gram of the average tar- acids from gas liquor 1,343 grams of oxygen.C. A. M. Determination of the Solidifying - Point of Commercial Paraffin. R. Kissling. (Chenz. Rev. Fett- 21. Hnrx-Ind., 1908, 15, 46-49.)-1t is here shown that in the determination of the solidifying-point by Shukoff's method considerable C T ~ O ~ S may result unless the conditions are invariably identical. Thus the results are influenced by such factors as the method and duration of shaking. If, for example, the tube be shaken and then allowed to stand, the thermometer becomes constant after a certain period of initial shaking, but the solidifying-point differs from that obtained by alternately shaking the tube and allowing it to stand until the paraffin froths and the thermometer becomes constant.To obviate such sources of error, the author has devised the following modification of the method : The Dewar's vacuum tube containing the melted paraffin is immersed to within about 10 mm. of the top in water a t a temperature about 5" C. above that of the solidifying-point expected, and as soon as the temperature of the paraffin is the same as that of the water the tube is vigorously shaken. When frothing of the paraffin takes place, the tube is allowed to stand, and the temperature taken from minute to minute, until three or more reading8 are identical, the mean solidifying-point being thus obtained. Owing to the influence of the varying proportions of the different constituents, the temperature curves of paraffins having the game mean solidifying-points may vary considerably. C.A. M. The Estimation of Tarry Substances in Mineral Oils. E. Lecocq. (Bull. SOC. Clzirn. Belg., 1908, 22, 81-87.)-Holde's method of extracting tarry substances from mineral oils by means of petroleum spirit or a mixture of 4 partsTHE ANALYST. 197 of alcohol with 3 parts of ether (cf. ANALYST, 1903, 28, 154, 299) has given good results in the author's hands, but in the case of cylinder oils containing paraffins the residual tarry matter frequently contains paraffin in spite of prolonged washing. The author therefore recommends distillation of the oil in a current of superheated steam before applying Holdds method.By this means both the solid and liquid hydrocarbons are removed, and the residue will finally consist only of tarry substances mixed with traces of oil adhering to the sides of the flask. A few glass b e d s are introduced to break up the residue, which is then treated with, e.g., 50 C.C. of the mixture of alcohol and ether. The closed flask. is vigorously shaken for some minutes, and allowed to stand for several hours, the liquid being then decanted and the deposit washed with the mixture of alcohol and ether until the filtrate ceases to be fluorescent. The residue may now be dissolved off the filter by means of a few C.C. of hot benzene, the solution evaporated in a tared basin, and the residue dried at about looo C. until constant in weight.Used with this modification, Holde's method gives exact results for all kinds of oil. With regard to the permissible limits for tarry matters in cylinder oils, the author considers that such oils should fulfil the following requirements : For Temperatures Corresponding to about 1 atmosphere Coinsponding to about 4 crtmos heres Corresponh'ing to about 5 to 7 aniiosphcres Corresponding to nhout 9 to 12 atmospheres Corresponding to higher pressures and for superheated steam Specific Viscosity a t 50'' C. 8 to10 About 15 About 20 About 25 30 t o 50, according to temperature of usage Distillation in Steam. About 75 per cent. should distil botweeii 150" and 130" C. About 7 5 per cent. between 150" arid 200" C. 7 5 per cent. between 160" and 220" c. 7 5 per cent. between 170" and 230" c.Variable ; highest observed, 75 per cent. between 2-10" iilld 260" c. Limit for Tarry Matter. None None 2.00 3.0 3.0 to 4.0, xcording to teiii 1)rrature o t usage. Limit for Pnrilffins. Per Cent. 3 '50 3.50 3.50 1.0 (locomotives), 3-50 (0 the I' machinery) 4.0 I I C. A. M. The Keeping Power of Fehling's Solution, and the Volumetric Process of Estimating Sugars with It. F. Watts and H. A. Tempany. (Jount. SOC. Chem. Ind., 1908, 27, 191-193.)-1t is stated that Violet's modification of Fehling's solution may be kept ready mixed for many months without fear of deterioration if light and air be excluded from it. For determining the end-point of the titration in the volumetric estimation of reducing sugars, the authors use potassium ferrocyanide solution acidified with acetic acid.A drop of the titration liquid is placed on a thrice-folded filter-paper, and when the liquid has soaked through the three layersI98 THE ANALYST. the lowest one is tested with a drop of the indicator. The reducing sugar content of the solution under examination should be confined within narrow limits (0.3 to 0.8 gram of sugar per 100 c.c.), in order to prevent the results obtained from being influenced by continual alterations of the bulk of the solutions during the titration ; the error introduced then becomes approximately constant. Allowance is also made for it if the Fehling’s solution be standardised under similar conditions. In the estimation of reducing sugar in raw sugars, a correction must be made for the reducing action of the sucrose itself.As the reeult of their experiments, the authors state that 1 gram of sucrose dissolved in 100 C.C. of water possesses a reducing power equal to 0.0033 gram of invert sugar dissolved in the same volume of water. w. P. s. The Chloramine Reactions of the Proteins and Industrial Applications. C. F. Cross, E. J. Bevan, and J. F. Briggs (Jounz. SOC. Chem. I d , 1908, 27, 263-264).-The authors have extended the work of Raschig (Chem. Zeit., 1907, 31, 926), who obtained monochloramine by the action of hypochlorites on ammonia, and have shown that the proteins and their derivatives, in virtue of their amino groups, form similar compounds. ,411 these chloramines possess the property of liberating iodine from potassium iodide and oxidising sodium arsenite, and thus resemble hypochlorites, but they differ from the latter in the fact that fhey are not destroyed by hydrogen peroxide and possess no apparent bleaching action.Soluble chloramines may exist in bleaching liquors which have been used on substances like flax, which contain residues of protein matters, and in the ordinary assay of such liquors they wopld wrongly be estimated as ‘‘ bleaching chlorine.” The amount of chloramine in these liquors may be estimated approxi- mately by destroying the hypochlorite with an excess of hydrogen peroxide, discharging this excess by acidified permanganate from a burette, adding potassium iodide and starch, and titrating the iodine liberated by the chloramine with & thio- sulphate. The chloramines of any insoluble protein substance may be prepared by means of hypochlorites, hypochlorous acid, or moist chlorine gas ; under this treatment gelatin becomes insoluble in hot water.The action tends to be superficial, owing to the fact that the chloramine produced constitutes a semi-permeable membrane through which further quantities of the chlorinating agent cannot penetrate. The active chlorine fixed in the form of chloramine is estimated, after thorough washing, by steeping the substance in a known excess of sodium arsenite for a sufficient length of time to ensure complete osmosis (about one hour) and titrating back the excess of arsenite by iodine. A dissolved protein-e.g., gelatin- may be estimated by means of the chloramine reaction by distributing a known weight of it on a porous material, such as cotton yarn, and exposing it, in the moist state, for about one hour in an atmosphere of chlorine gas. The excess of chlorine is then removed most conveniently, not by washing, but by suspending the yarn in a strong current of air from an electric fan for at least an hour and a half.The estimation of the fixed chlorine is then carried out, by means of standard arsenite. The value for air-dry gelatin determined in this way was 15.4 per cent. of active chlorine. This empirical factor may be used for the estimation of gelatin inTHE ANALYST. 199 paper, etc. ; previous combination of the gelatin with formaldehyde does not affect the result. Proteins in solution may be treated with a basic solution of hypochlorite, and estimated by the peroxide method mentioned above.A rapid qualitative test for the general or localised presence of proteins in natural or manufactured products is carried out as follows: The material to be tested is either damped with water and exposed to an atmosphere of chlorine gas for half an hour, or it is steeped directly in a dilute acidified solution of bleaching-powder. The chlorinated substance is rinsed in water, and the excess of chlorine is removed by immersing the substance for five minutes in a 2 per cent. solution of sodium phosphate previously heated to 45' C. The material is then treated with a solution of potassium iodide and starch, a blue stain being developed in those places where protein is present. The sodium phosphate also precipitates traces of ferric salts which would liberate iodine in the acid state.J. F. B. Quantitative Estimation of Phenolic Hydroxyl Groups. J. Herzog and V. Hancu. (Ber. deut. Chem. Ges., 1908, 41, 638-639.)-Herzog (Bcr. deut. Chena. Ges., 1907, 40, 1831) has shown that diphenylurea chloride yields well crystallised diphenylurethanes with phenolic substances, and that these compounds are very readily saponified by potassium hydroxide yielding diphenylamine, which is volatile with steam, and the potassium salt of the phenol, which is not volatile. The saponi- fication of these urethanes affords a convenient means for the estimation of the percentage of hydroxyl groups in the original phenol. For this purpose about 1 gram of the urethane and 8 C.C. of alcohol are heated with an excess of potassium hydroxide in 8 pressure-bottle for one hour in a boiling water-bath. The product is transferred to a distillation-flask, the bottle being rinsed out twice with 2 C.C.of alcohol. The distillation with steam, which follows, should be conducted slowly, so that the distillate containing the diphenylamine comes over drop by drop. Any solid deposit in the condenser is removed at the end of the distillation by allowing the condenser to become warm. After standing for twenty-four to forty-eight hours the distillate becomes clear, and the diphenylamine is collected on a tared filter and dried at 30' C. J. F. B. Quantitative Estimation of Methoxyl and Methylimino Groups. A. Kippal. (Ber. dezd. Chem. Ges., 1908, 41, 820-821.)-The author records a case- that of the methylic ether of @-hydroxypyridine betaine-in which the determination of the inethoxyl group by Zeisel's method gave results which were much too low owing to the fact that, under the action of boiling hydriodic acid, the methyl group is liable to migrate and attach itself to the nitrogen.On the other hand, the method of Herzig and Meyer, for the inclusion in the estimation of the methyl residue attached to nitrogen, gave too high results owing to the splitting up of the betaine, with the formation of methyl iodide from other portions of the molecule. J. F. B. Action of Ozone on Compounds with Triple Bonds. E. Molinari. (Ber. dcut. Chem. Ges., 1908, 41, 585-589.)-1n a recent paper (ANALYST, 1908, 22) the author proposed a method for the differentiatios of compounds with triple bonds200 THE ANALYST.from those with double bonds by means of ozone. The observations on which this method was based met with a direct contradiction on the part of Harries (ANALYST, 1908, 99). The author now reaffirms all his previous statements, and attributes the difference between his observations and those of Harries to the fact that he used ozonised air, whilst Harries always employed ozonised oxygen. J. F. B. Physical Constants of Mixtures of Water and Glycerin. P. M. Strong. (Clwm. Zeit., 1908,32, 334.)-The values given in the following table were determined at 18" C., the specific gravity being found by means of a Westphal's balance, the refractive index in Abb6's refractometer, the surface tension by means of a Duclaux's pipette of 5 C.C.capacity, delivering 100 drops of distilled water at 15" C., and the viscosity in Ostwald's viscosimeter : Glycerin. Per Cect. 0 10 20 30 40 50 60 70 80 90 100 Specific Gravity. 1.000 1 *0295 1.0681 1.1094 1,1340 1.1602 1.1860 1.2142 1.2330 1.2599 1.0800 (?) Refractive Index. 1.3277 1.3390 1.3528 1.3650 1.3787 1.3891 1.4020 1.4129 1.4386 1.4529 1.4650 Surface Tension. Number of' Drops. 102 106 110 114 119 124 130 136 147 158 172 Viscosity Coefficient. loO0O 1.3137 1.7197 2-5340 3.6451 5.4108 7.0716 14.2094 48.1632 81.0256 777 -5382 C. A. &I. The Goldenberg Method for the Estimation of Tartaric Acid in Argol, Wine Lees, and other Crude Materials containing Tartaric Acid. Chemische Fabrik, formerly Goldenberg, Geromomt and Co. (Zeit. Anal. Chem., 1908, 47, 57-69.)-The following manner of carrying out this process is put forward in the hope that it may form the basis of an international method for estimating tartaric acid in crude articles of commerce.Six grams of the sample containing more than 45 per cent. of total tartaric acid, or 12 grams if the sample contain less than 45 per cent. of the acid, are digested for ten minutes with 18 C.C. of hydrochloric acid (specific gravity 1-10), The whole is then transferred to a 200 C.C. flask and diluted to the mark with distilled water. After mixing, the contents of the flask are filtered through a dry filter. One hundred C.C. of the filtrate are placed in a 300 C.C. beaker, in which 10 C.C. of 66 per cent. potassium carbonate solution have been placed pre- viously, and the mixture is boiled for twenty minutes in order that any calcium car- bonate may be converted into the crystalline form.The solution, together with the precipitate, is then rinsed into a 200 C.C. flask, cooled, diluted with water to the mark, mixed and filtered. One hundred C.C. of the filtrate are evaporated to a volume ofTHE ANALYST. 201 15 c.c., and, while the solution -is still hot, 3.5 C.C. of glacial acetic acid are added slowly, with constant stirring, the mixture being then stirred for a further five minutes. After the lapse of ten minutes, 100 C.C. of 95 per cent. alcohol are added, and the stirring is continued for five minutes. The whole is next allowed to stand for ton minutes, then filtered, and the precipitate is washed with alcohol until free from acidity. The filter and precipitate are then washed into a porcelain basin with 200 C.C. of hot water, and the boiling solution is titrated with 2 sodium hydroxide solution, using litmus paper as indicator. The sodium hydroxide solution must be standardised by titration on a known quantity of pure potassium hydrogen tartrate. As no allowance is made for the volume of the insoluble matters when the sample is made up to the volume of 200 c.c., the results obtained are corrected as follows : in the caw of samples containing less than 45 per cent. of total tartaric acid 0.80 per cent. is subtracted from the quantity of acid found ; for samples containing from 45 to 60 per cent. the correction is 0-30 per cent. ; for those containing from 60 to 70 per cent., 0.20 per cent.; whilst no correction is applied to the result if the sample contain more than 70 per cent. of total tartaric acid. w. P. s.

ISSN:0003-2654    

DOI:10.1039/AN9083300193

出版商:RSC    

年代:1908

数据来源: RSC

摘要:

THE ANALYST. 201 INORGANIC ANALYSIS. The Affinity Constants of Bases as determined by the Aid of Methyl- Orange. V. H. Veley. (Trans. Chem. SOC., 1908, 93, 652-666.)-The author has extended the work of which a preliminary account has already appeared (ANALYST, Results are given for the hydrochlorides of (1) bases not containing an alkyl grouping, (2) aliphatic amines, (3) amino-acetic acids, and (4) uric acid derivatives. As regards hydrazine in (1) and all cases of (3), it is shown that the results obtained by the methyl-orange method are concordant with those obtained by the electric conductivity method, although the dilutions were about forty to eighty times greater. The tentative conclusion was drawn that either there is a limiting value of V in the Arrhenius equation Kb/Kto = (1 - z)V/x2, or that the hydrolytic reaction becomes reversible. As regards cases of (4), the general agreement of the results obtained by the methyl-orange method with those of the solubility method was con- sidered, although the increase of hydrolysis relative to dilution is less than that required by Arrhenius' formula.1908, 54). Valuation of Barium Peroxide. A. Chwala. (.Zeds. aizgczo. Chenz., 1908, 21, 589-592.)-The available oxygen in barium peroxide can be accurately determined gasometrically by Quincke's method by dissolving the substance in dilute hydrochloric acid, and allowing this solution to react with an alkaline solution of potassium ferricyanide, the evolved oxygen being measured. The reaction is best carried out in the flask devised by Lunge, which, in addition to the central compartment containing the ferricyanide solution, must be provided with a receptacle from which the hydroohloric acid can be added to the barium peroxide in the outer compartment without disturbing the ferricyanide solution.This receptacle may consist of a small202 THE ANALYST. tube which can be readily inverted in the outer compartment, or else of a small siphon tube, provided with a tap near its middle; both limbs of this siphon are inserted in the stopper, the tube is filled with hydrochloric acid (2 or 3 c.c.), the whole apparatus connected, and the acid allowed to flow on to the peroxide by opening the tap. Accurate results are also obtained by the following iodometric method : To an emulsion of 0.1 gram of barium peroxide and 200 C.C.of water, contained in a flask, 100 to 150 C.C. of a, standard solution of potassium ferricyanide (65.9 grams per litre) are added. As soon as the reaction slackens, the liquid is slowly heated to boiling, with occasional shaking. After boiling for one or two minutes, the liquid is allowed to cool somewhat, and 5 C.C. of hydrochloric acid (specific gravity 1.15) and then 1.3 to 1.5 gram of zinc sulphate dissolved in the smallest quantity of water are added, followed by 2 or 3 grams of potassium iodide. The flask is stoppered, well shaken, and heated at 40 to 4 5 O C. for ninety minutes. The amount of iodine liberated is then determined, either in slightly acid solution with thiosulphate, or else in alkaline solution with arsenite solution.I n either case, an excess must be added, and then titrated with iodine solution. A blank should be carried out at the same time on the reagents, One molecule BaO, corresponds to two of K,Fe(CN),, and one molecule of the latter liberates one atom of iodine. The function of the zinc sulphate is simply to render the ferrocyanides insoluble. Useful results can also be obtained by dissolving the barium peroxide in the minimum quantity of dilute hydrochloric acid, adding dilute sulphuric acid, and titrating with potassium permanganate solution. The results are constantly about 0.5 to 0.7 per cent. too low. Substitution of the sulphuric acid by manganese sulphate, according to Lob, leads to similar results. Kassner's method ( d ~ c h . Pl~amz., 1890, 228, 432) gives results several per cent. too low.Ordinary iodometric methods-e.g., distillation with hydrochloricacid and potassium iodide-also give very low results. A. G. L. The Influence of Temperature on the Electrolytic Precipitation of Copper from Nitric Acid. J. R. Withrow. (Jozun. Amer. Chem. SOC., 1908, 30, 381-387.)-The author finds that, using stationary cathodes, 0.25 gram of copper was completely precipitated in thirteen hours from both sulphate and nitrate solutions (125 c.c.) containing no free acid, at a temperature of 25" C., and with a current of N.D,,,=0*25 ampire at 3-3 to 2.6 volts; the deposit obtained from the nitrate solution whs, as usual, more adherent than that given by the sulphate solution. Addition of 0.25 C.C. nitric acid to the sulphate solution improved the character of the deposit without retarding the deposition ; further addition of nitric acid, up to 2.5 c.c., did not improve the deposit, and caused but little retardation ; but beyond this amount nitric acid led to slow or incomplete deposition.When the copper sulphate solution containing 0.25 C.C. of nitric acid in 125 C.C. of solution was kept at 40" C. during electrolysis, the time necessary was shortened to seven hours; at 60" C. it was six hours; whilst further heating did not hasten the deposition, and heating above 70" C. had the reverse effect. A. G. L.THE ANALYST. 203 Estimation of Ferrous Iron in Minerals. N. Knight. (Chenz. News, 1908, 97, 122.)-It has been pointed out by R. Manzelius (Geological Survey of Sweden) that considerable oxidation of the ferrous iron present in minerals and rocks occurs if the sample be ground to a fine powder, and that a more accurate result may be obtained by working on the coarsely ground sample.The author found that specimens of siderite, showing 2.68 and 2-67 per cent. of ferric oxide when in a coarsely ground condition, gave a content of 3-26 and 3.11 per cent. respectively on subsequent reduction in an agate mortar to a fine powder. The oxidation is promoted by the heat caused by friction. The amount of ferric oxide in the minerals was determined by dissolving about 1 gram in hydrochloric acid in an atmosphere of carbon dioxide, quickly cooling the solution, and adding barium carbonate until all the ferric iron was precipitated. The precipitate was rapidly filtered, washed thoroughly with cold water, redissolved in acid, and the iron pre- cipitated by ammonia after the removal of the barium as sulphate.A. R. T. Purification of Hydrogen from Arsenic. H. Reckleben and G. Locke- mann. (Zed. angew. Clzem., 1908, 21, 433-436.)-A saturated solution of potassium permanganate is recommended as the most suitable fluid absorption agent for arsenic in hydrogen required for laboratory purposes. A 5 to 10 per cent. solution of silver nitrate also gives good results, and has the advantage of enabling an approximate estimation of the amount of arsenic to be made from the quantity of precipitate. A solution of silver nitrate is also valuable as a final test of the purity of the washed gas. Mercuric chloride solution only absorbs the arsenic effectually so long as the resulting precipitate appears white or pale yellow, and as soon as it becomes orange-coloured arsenic may be carried on by the gas.Of solid absorption agents cupric oxide takes the first place, since it not only retainsjhe arsenic, but also other impurities (hydro- gen sulphide), in the hydrogen. Iodine loosely packed with cotton-wool in the tube is also an effective absorbent for arsenic, but the hydrogen must subsequently be conducted through some agent, such as potassium iodide solution, to retain the resulting hydriodic acid, and traces of iodine mechanically carried forward. C. A. M. Estimation of Magnesia in Magnesite. J. Mayrhofer. (Zeit. angezu. Chem., 1908,’21, 592.)-The author finds that Pozzi-Escot’s method (Ann.Chirn. anal. 1902, 7, 126) for the direct determination of magnesia without previous removal of alumina, ferric oxide, or lime, gives unreliable results. He has, however, obtained values differing by less than 0.3 per cent. from those obtained in the ordinary way by adding to a solution containing about 0-1 gram of magnesia, after freeing from silica, 5 C.C. of concentrated sulphuric acid, 100 C.C. of a solution containing 100 grams of citric acid and 333 C.C. of ammonia (specific gravity 0.91) per litre, 20 C.C. of a 10 per cent. solution of sodium phosphate, and 15 C.C. of concentrated ammonia, in the order named. The warm solution is well stirred for five minutes, filtered after standing for two hours, and the precipitate treated as usual. A. G. L.204 THE ANALYST.Detection of Mercuric Chloride in Nitro-Cellulose. J. Moir. (Chem. News, 1908, 97, 133.)-Mercuric chloride is frequently added to wet collodion-cotton to prevent its becoming monldy, and also to make defective material pass the official heat test. Owing to its affinity for organic matter, this mercuric chloride cannot readily be separated, excepting by volatilisation. The first of the two methods described is a combination of Hargreave and Rowe’s process with that of Mann. (1) A piece of ignited silver foil is placed in a flask containing some of the moist cotton, and the flask immersed in boiling water. Air is aspirated through the flask, and then through bulbs containing 2 per cent. sulphuric acid. After two hours any mercury which has escaped the silver foil is deposited on it by the electrolysis of the sulphuric acid, using the silver as the anode, with a current of 4 volts for two hours, The mercury deposited on the dried silver foil is sublimed on to a glass microscope-slide. (2) The cotton is extracted with a hot, very dilute solution of potassium iodide, and the solution electrolysed as before, after evaporation to small bulk.Iodine collects on the platinum basin used as cathode, and any mercury on the gold or silver foil anode. The mercury is then sublimed. A. R. T. Estimation of Lead, Copper, and Silver in Complicated Organic Salts. M. Rind1 and H. Simonis. (Ber. clezit. Clzcm. Gcs., 1908,41,838-840.)-The authors have submitted the various methods available for the estimation of lead, copper, and silver in organic compounds to a critical investigation.Lead.-The most convenient and accurate method is the simple ignition of the substance with strong sulphuric acid. I n special cases the estimation of the lead may be combined with that of sulphur by Carius’s method, provided there is more than one equivalent of sulphur to one of lead--e.g., lead salts of sulphonic acids. The excess of sulphuric acid is then determined by means of barium chloride in the filtrate from the lead sulphate. Copper.-Neither of the methods recommended by Hans Meyer-viz., burning with ammonium nitrate or with mercuric oxide-is accurate. The best method is that recommended by Liebermann, simple ignition with strong sulphuric acid, the copper remaining as cupric oxide. SiZ?ieT.-With silver salts containing halogens the usual method of heating in a tube with fuming nitric acid, with the addition of the potassium salt of the halogen, gives good results if the silver precipitate be very thoroughly washed. Evaporation of the substance with aqua regia (in the case of bromo-compounds with hydrobromic acid) is more rapid. Vanino’s method of reduction with formal- dehyde and potassium hydroxide may also be applied to silver salts containing sulphur, but it is necessary to reduce several times. Silver salts containing sulphur or nitrogen leave metallic silver on incineration, but the former require heating to fusion. By the addition1 of a weighed quantity of silver nitrate, the estimation of silver may be made simultaneously with that of the halogen by Carius’s method, the excess of silver being determined in the filtrate. J. F. B.

ISSN:0003-2654    

DOI:10.1039/AN9083300201

出版商:RSC    

年代:1908

数据来源: RSC