摘要:

T.EE ANALYST. JULY, 1896. NOTE ON THE COMPOSITION O F TWO DEPOSITS FORMED I N WATER-PIPES. BY J. -4. .4ND E. W. VOELCKEIE. (Bend at the Meeting, May 6, 1896.) As in considering the suitability of any water for general domestic use, the question of its action upon metallic pipes is one of great importance, we venture to bring before the Members of the Society two cases which may be of interest. The first case to which we would refer is one that occurred recently, and which shows how the action of a soft water on galvanized iron pipes may give rise to serious inconvenience. We had lately occasion to examine a deposit which had formed in a pipe con- nected with the hot-water apparatus of a private house in the country. The pipe in question was completely blocked up with a white deposit, and the owner of the house was very disappointed to find that the water which we had previouslyreported to be a very soft and pure one, and suitable for general domestic use had, after a, comparatively short time, given rise to a deposit in the hot-water pipes.Upon analysing the material we found that it contained no lime, but consisted almost entirely of a basic carbonate of zinc, together with oxide of zinc. The owner was under the impression that the deposit was due to lime.170 THE ANALYST. The analysis of the deposit was as follows : Oxide of iron ... ... ... ... ... ... ... 0.56 Alumina ... ... ... ... ... ... ... 0.59 Basic carbonate of zinc ... ... ... ... ... 64-32 Oxide of zinc ... ... ... ... ... ... ... 21.95 Silica ... ... ... ...... ... ... ... 4.07 On inquiry we found that the water was lifted by a ram to the height of 300 feet, along about half a mile of galvanized iron pipes. These appear to have been very rapidly attacked by the water, the zinc being dissolved and deposited in the pipes at those points where the water was very hot, and also in the boiler and hot-water cylinder. The next instance shows the action upon iron of a very hard water containing a The well-water in question contained over 40 grains per gallon of total solids. It was noticed that on the pump-rods in the well a black scale was formed, and in the stand-pipe there was a considerable amount of deposit. The analysis of the scale and of the deposit revealed the presence of a notable quantity of free sulphur. I n the deposit in the stand-pipe the free sulphur amounted to over 5 per cent.This, probably, is to be accounted for by the action of the organic matter on the sulphates in the water, sulphuretted hydrogen being produced and then absorbed by the hydrated oxide of iron formed by the rusting of the iron pipes, while the subsequent oxidation resulted in the liberation of sulphur, the action being the same as takes place when the oxide froin gas-purifiers is exposed to the air. good deal of sulphate of lime and organic matter. The analyses were : Ferrous oxide ... Ferric oxide ... Ferrous sulphide Lime ... ... Carbonic acid ... Sulphuric acid ... Free sulphur ... Silica ... ... Alumina ... Deposit in Stand-pipe. ... ... ... 11-31 ... ... ... 2-72 ... ... ... ... 7.11 ...... ... ... 11-45 ... ... ... ... 1-42 ... ... ... ... 5.20 ... ... ... ... 8.55 ... ... ... ... 2.31 ... ... ... ... 38-09) ... Scale on Pump. ... 4.78 ... 2.64 ... 48.63 ... 37-08 ... 0.46 ... 1.65 ... 0.90 ... 0.93 DISCUSSION. The PRESIDENT said that the explanation given of the presence of free sulphur was very interesting, though at first sight it might not appear to be quite satisfactory. Of the actual presence of free sulphur, however, there could be no doubt. A good deal of interest attached to the deposit in the pipe, on account of the very highly basic character of the carbonate. Apparently it wae not the ordinary basic carbonate which was usually formed on the surface of galvanized pipes and on zinc ; that was a much less basic substance than this. Roughly speaking, the ratio of zinc to Co, was about 48: 1, which was quite exceptional, and seemed to point rather to a mixtnre of zinc oxide and the ordinary basic carbonate of zinc than to any other very definite chemical compound.T E E ANALYST.171 Dr. J. A. VOELCKER said that upon first inspecting the pipe in question, he naturally thought that the deposit was of the ordinary nature, viz., carbonate of lime. His brother (Mr. E. W. Voelcker), however, noticed that it was particularly soft ; this led to a further examination of the deposit, when it was found that there was no lime at all in it, but that it consisted mainly of carbonate of zinc. On referring back to the analysis of the water, which had been made some time previously, it was found that the water was distinctly soft, if containing only about 6 grains of total solids per gallon.The portions of the pipes upon which the deposit had mostly formed were those nearest the boiler. The deposit contained something like 64 per cent. of basic carbonate, and some excess of oxide of zinc, which might have been due to change in the basic carbonate consequent on the heating. The instance seemed to be of interest, as showing clearly the production of sulphuretted hydrogen in waters containing a good deal of organic matter, together with calcic and other sulphates. Dr. DYER inquired whether the acidity of the first water had been taken with phenolphthalein. Mr. E. W. VOELCKER said that the acidity had not been determined.* The water was from a Welsh mountain-stream, and contained very little organic matter. The oxygen absorbed was a mere trifle, and the water was not coloured like a, peaty water would be. The other water, of course, was of a different kind. It might be interesting to do this. Mr. KITTO inquired what amount of chlorine was present. Mr. E. W. VOELCKER said the chlorine amounted to about 1 grain per gallon. As regarded the composition of the carbonate, there certainly was a large quantity of oxide of zinc present in the deposit, but ordiqary carbonate of zinc, would, without doubt, have been decomposed by the high temperature and pressure t o which the deposit had in all probability been subjected.

ISSN:0003-2654    

DOI:10.1039/AN896210169b

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

TEE ANALYST. 171 THE COMPOSITION O F HUMAN FAT. BY C. A. MITCHELL, B.A. (Read at the Meeting, May 6, 1896.) ALTHOUGH it is not probable that members of this Society will be frequently called upon to make an analysis of human fat, yet one can easily conceive the possibility of such a case occurring, and I have therefore thought that, apart from their purely scientific interest, my figures might have a, practical value. Human fat appears to have been but little studied since the days of Chevreul and Heintz-at least, no description of its characteristics is to be found even in books .of this sample showed the following constituents : -X This has since been done in o fresh sample, and the water found to be slightly acid. The analysis Grains per gallon. Total solids ... ... ...... ... 6.160 Chlorine ... ... ... ... ... 0.960 Nitric acid ... ... ... ... ... traces Oxygen absorbed ... ... ... ... ... 0.022 Ammonia ... ... ... ... ... ... none.172 THE ANALYST. dealing specially with physiological chemistry. Chevreul" found that it consisted of an olein and stearin, the latter being distinguished from mutton stearin by yielding 6 L margaric," and not stearic acid. Heintzt came to the conclusion that the compo- sition of the fat was of a more complex nature, and that, in addition to olein end palmitin, there were small quantities of several other acids, one of them being a liquid acid. The specimen of fat which I have examined, and for which I am indebted to the kindness of Dr. Arnold Chaplin, was separated from the tissue at as low it temperature as possible.It was of a pale yellow colour, and had a consistency somewhat less than that of butter. On crystallization from ether there was only a slight deposit, which, when washed with ether and dried, melted at 51.5" C. Under the microscope the crystals had some resemblance to those frequently obtained from flare lards, being arranged in fen-shaped bunches, while the individual crystals had the characteristic chisel-shaped ends. The determination of the chemical and physical constants of the fat gave the following figures : FAT, Specific Gravity at 25" C. (Water at 25" = 1) ... 0.9033 Melting-point ... ... ... ... ... ... 17.5" Solidification-point ... ... ... ... ... 15" = Equivalent ... ... ... ... ... 287 Reichert Value (2.5 grammes) ...... ... 0.3 alkali. Acidity No. (1 gramme) ... ... ... 6.3 mgs. KOH = 0.32 Saponification No. ... ... ... ... ..+ 195 ... per cent oleic acid. Bromine Heat Vslue .. ... ... ... ... 11-3" C. = Iodine Value, 11.3 x 5.5 ... ... ... 62.15 Iodine Value (Hiibl) ... ... ... ... ... 61.5 Melting-point ... ... ... ... ... ... ... ... 35.5" Solidification-point . . . ... ... ... ... ... ... 30-5" FATTY ACIDS. Iodine Value ... ... ... ... ... ... 64 Iodine Value of Liquid Acids. ... ... ... ... ... 92.1 I n order to obtain some idea as to the nature of the fatty acids, Twitchell's modification of Jean's method of fractional precipitation was employed (ANALYST, xx., p. 165). 1.9478 grammes of the fatty acids (iodine number 64) were dissolved in 25 C.C. of 95 per cent. alcohol ; 1-5 grammes of lead acetate dissolved in 10 C.C.of the same alcohol were added, and the flask well corked, allowed to stand over-night. I n the morning some of the liquid was filtered, the acids recovered by shaking with ether and hydrochloric acid, and their iodine number determined. The precipitate warr well washed with alcohol, the fatty acids recovered, dried, and weighed, and their iodine number also determined. I n each case precautions were taken to prevent oxidation. The results obtained were : Grammes. Iodine No. Per cent. Solid Acids ... ... ... .9779 37 50-2 Liquid Acid (by difference) ... ... -9699 92 49.8 'r .I:eclwrcAes s'ur les Corps Gras, 1823. 5. Poggz. Annal., 1851, p. 230.THE ANALYST. 173 The acids from the filtrate were liquid at 15" C., while those from the precipitate melted at 35.5" C., and had a molecular equivalent of 278.From these figures the amount of liquid and solid acids can be calculated. Per cent. ... ... Liquid Acids in filtrate ... ... ... ... 49.8 ,¶ ,, precipitate reckoned as Oleic Acid ... ... 20.6 37 x 50.2 - 18.57 100 0.9 - - - Total Liquid Acids ... ... ... ... ... ... ... 70.4 ... ... ... .. ... 90.9 64 x 100- - With Iodine No. 7om4 From this it appears that the liquid acids probably consist of oleic acid, with a, small amount of a more unsaturated acid, possibly linolic. With regard to the solid acids, the high molecular equivalent (278) of the lead precipitate, of which only 20 per cent. is accounted for by the liquid acids, leads t o the conclusion that stearic acid, or some other acid of high molecular weight, i s present.Further evidence of the composition of the solid acids was obtained by crystal- lizing the fatty acids from 70 per cent. alcohol. The crystals, after being well washed with the same alcohol and dried, melted at 50.5" C. This melting-point being lower than that of any mixture of stearic and palmitic acid in Heintz's table, points to the presence of myristic acid, since the precipitate was quite free from liquid acids. The filtrate, on standing, yielded a second deposit, which also melted at 50-5" C. Human fat, therefore, would seem to consist of about 70 per cent. of liquid acids, principally oleic acid, 30 per cent. of solid acids, probably palmitic with small amounts of stearic and myristic acids, and traces of lower volatile acids.DISCUSSION. The PRESIDENT said that Mr. Mitchell's figures were very valuable, and he hoped to see them incorporated in future text-books on physiology, in supersession of the very imperfect data at present available on the subject of human fat. The fact that the results now brought forward were perfectly novel, to a certain extent prevented discussion of them ; but they were certainly worthy of consideration, and credit was due to Mr. Mitchell for bringing them forward. Mr. HEHNEH said he would like to ask Mr. Mitchell for some further explanation of the grounds upon which he assumed that the fluid fatty acids consisted chiefly of oleic acid, with a small amount of linolic acid. H e (Illr. Mitchell) had, by means of their lead salts, divided the acids into liquid and solid.He (Mr. Hehner) had shown to the Society that the separation of the lead salts by means of ether was at most but a partial one, and this was borne out by Mr. Mitchell's figures. For instance, the '' solid " fatty acids having an iodine absorption of 37 per cent., should not, theoreti- cally, have had any iodine absorption at all, if the process of separation had worked perfectly; and from the fact that the original fat had an iodine absorption of 61, it would seem that separation had really been effected very imperfectly. Certainly the " liquid " fatty acids had an iodine absorption of 92, practically that of oleic acid, but was it not possible that these liquid fatty acids contained a considerable quantity of174 THE ANALYST.the solid acids ? At all events, this was the conclusion which he (Mr. Hehner) had arrived at from his own investigations in connection with this process of separation. With lards, to which human fat appeared to have a great resemblance, this process seemed also to give very variable results. The figures which Dr. Muter had published in this connection all showed iodine absorptions of about 90 or 91 for the fluid acids, but further investigation had shown that, from American lard, at all events, much higher figures were obtained, indicating that there must have been a consider- able quantity of another fatty acid besides oleic acid, and, considering that solid saturated fatty acids were undoubtedly included in the fluid onss, the amount of the unsaturated fatty acid would be larger than appeared from the iodine absorption.He therefore did not think it followed that because a liquid fatty acid obtained in this way had an iodine absorption of about that of oleic acid, that oleic acid was neces- sarily present. In the case of the pig, the lard varied very considerably, according to the part of the body from which it was obtained. Also whether Mr. Mitchell haddetermined the Valenta number, and the refractive index in the oleorefractometer. Mr. MITCHELL, referring to the question of the iodine absorption of the liquid fatty acids, said that no system of identification which depended simply upon the iodine absorption test could be regarded as conclusive, but that since, so far as he was aware, no acid absorbing less than 90 per cent, of iodine had yet been found in fats, he considered it probable that when an iodine number of about 90 was obtained in the liquid acids prepared by Twitchell's method it represented oleic acid. Twitchell had shown that in his process of separation there was a fractional pre- cipitation, the lead salt of oleic acid being precipitated first, then that of linolic, and finally that of linolenic acid. He therefore calculated any iodine absorption in his precipitate as oleic acid. Since by this fractionation process he (Mr. Mitchell) had found that the acids from the filtrate only absorbed 92 per cent. of iodine, whereas Twitchell frequently had an iodine absorption of over 100, it was highly probable that acids more unsaturated than oleic acid were only present in small quantities. At the same time, the data were insufficient for anything more than a probable conjecture. He believed that the fat he had examined was from the kidneys. He had not determined either the Valenta number or the refractive index. Mr. BEVAN inquired what part of the body the fat had been taken from.

ISSN:0003-2654    

DOI:10.1039/AN8962100171

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

174 THE ANALYST. ON THE COMPOSITION AND ANALYSIS OF COMMERCIAL CREAM OF TARTAR. BY ALFRED H. ALLEN. (Read at the Meeting, June 3, 1896.) WHEN prepared by boiling crude tartar or ‘( argol” with water, filtering, and crystallizing the salt from the clear liquid, cream of tartar always contains more or less calcium tartrate, which, though nearly insoluble in cold water, dissolves with moderate facility in a hot solution of acid tartrate of potassium. In a paper read byTHE ANALYST. 175 me before this Society in April, 1880, I described some experiments made to ascertain the extent to which calcium tartrate could occur unavoidably or legitimately in cream of tartar. To avoid reference, I may recapitulate the nature and results of these experiments, as described in THE ANALYST, vol.v., p. 114. Pure calcium tartrate was prepared by precipitating calcium chloride by neutral sodium tartrate prepared from pure tartaric acid and sodium carbonate. The analysis of the salt showed that it was strictly neutral in composition. Pure potassium hydrogen tartrate was prepared by dividing a solution of pure tartaric acid into two equal portions, neutralizing one with potassium carbonate, and adding the other. Weighed quantities of the last product were dissolved in known measures of boiling water, an excess of moist tartrate of calcium added, the liquid boiled for a, short time, filtered boiling hot, and the crystals of cream of tartar deposited on the cooling of the filtrate were analysed. In this manner, products were obtained which contained as much calcium tartrate as would dissolve in the measure of boiling solution of tartrate of potassium employed.The only variable condition was the pro- portion of water used. It was not found practicable to dissolve the acid tartrate of potassium in fifteen times its weight of boiling water. Hence, one in twenty-five was the strongest solution employed. The following are the percentages of insoluble ash and anhydrous neutral calcium tartrate contained in the different products : Proportion of Water used. Insoluble Ash. x 1.88 = CaC,H,O,. 1. ... 25 parts ... 3-10 per cent. ... 5-82 per cent. 1 A. ... 25 ,, ... 3-28 ,, ... 6.16 ,, 2. ... 50 ,, ... 3.40 ,, ... 6-39 ,, 2 A. ... 50 ,, ... 3.30 ,, ... 6-20 ,, 3. ... 75 ,, ... 4-40 ,, ... 8.27 ,, 3 A. ... 75 ,, ...4-80 ,, ... 9.02 ,, Froin these results it appears that the proportion of calcium tartrate contained in cream of tartar is greater the larger the proportion of water employed for solution ; but that, with the quantity of water likely to be used in practice, the product will not contain more than nine or ten per cent. of calcium tartrate. This is fully confirmed by the experience of myself and others as to the composition of commercial cream of tartar. One or two per cent. in excess of ten may be allowed by the Public Analyst as a margin, but it may safely be concluded that any sensibly higher proportion of calcium tartrate is not a normal constituent of the sample. Cases have occurred in which crude tartar or argol has been substituted for cream of tartar, which is a product refined by crystallization from water.I n crude tartar the percentage of calcium tartrate found may be very high, especially if it be derived from plastered wine ; but in such cases more or less sulphates will also be present. I n a sample of cream of tartar submitted to me some years since I found as much as 20 per cent. of calcium sulphate. This was not crystallized, as it would have been if derived from the plastering process, but had apparently been intentionally added as an adulterant, probably in the form of plaster of Paris. According to the British Pharmacopoeia of 1867, " 188 grains (of cream of tartar)176 THE ANALYST. heated to redness till gas ceases to be evolved, leave an alkaline residue, which requires for exact neutralization 1,000 grain measures of the volumetric solution of oxalic acid.” Nothing is said here about operating on the filtered extract of the ash, so that the neutralizing power of the calcium carbonate derived from the calcium tartrate would be included.As a matter of fact, 1813.1 grains of pure potassium hydrogen tartrate are required to neutralize 1,000 grain-measures of normal oxalic acid, so that the test leaves no room €or any impurity whatever, except calcium tartrate, and the larger the proportion of this substance there is present the better the sample will1 appear. By a coincidence, the molecular weights of KHT and Caq are identical, but the residue left on igniting the latter will have twice the neutralizing power of that yielded by the former. Hence the residue from 188 grains of calcium tartrate would neutralize 2,000 grain-measures of normal acid.I n the British Pharmacopceia of 1885, the foregoing test for the purity of cream of tartar was modified, the directions being as follows :-‘‘ Dried on a water-bath, 204 grains, heated to redness till gas ceases to be evolved, leaves an alkaline residue, which, when treated with distilled water, filtered, and well washed, yields a clear solution requiring for exact neutralization at least 1,000 grain-rneasures of the volumetric solution of oxalic acid.” This amount of acid corresponds to 92.15 per cent. of potassium hydrogen tartrate. Most analysts will avoid using the clumsy amount of the sample prescribed in the British Pharmacopia, and will operate on 5 grammes, which, when ignited, should give a soluble extract which neutralizes not less than 24.4 C.C.of normal acid. I t will be observed that the British Pharmacopceia test allows less than 8 per cent. for calcium tartrate and all other impurities. I n a recent case at Belfast in which a vendor of cream of tartar was prosecuted on the certificate of Sir Charles Cameron for selling an article adulterated with 17.93 per cent. of tartrate of lime, Mr. S. Templeton, F.I.C., of the Belfast School of Applied Chemistry, was called for the defence. In the face of the very precise standard of purity adopted by the Pharmacopccia, Mr. Templeton stated that the British Pharmacopoeia allowed a variable quantity of calcium tartrate up to about 15 per cent., and that he would consider cream of tartar containing that proportion as a fairly good commercial article ! When taxed with this statement iu the Belfast press Mr.Templeton argued that the Pharmacopceia test only refers to 20.9 per cent. of the radical potassium, and that it is not justifiable to assume that all this is present as acid potassium tartrate. Mr. Templeton further suggests that some may be present as neutral potassium tartrate, but he does not explain how he would account for the presence of any notable quantity of such an extremely soluble salt in an article prepared after the manner of cream of tartar ; and, unfortunately for Mr. Templeton’s argument, the British Pharmacopoeia test includes any neutral potassium tartrate, and credits it as bitartrate ! Not only does it do this, but 116 parts of K2F produce on ignition as much K2CO:, as is yielded by 188 of KHT; so that if a sample consisted wholly of neutral potassium tartrate it would show by the British Pharmacopoeia test 162 per cent. of acid tartrate ! The character (of commercial cream of tartar has materially improved of late years, and an article which might be tolerated in 1884, when vol.i. of my L L Coxn-THE ANALYST. 177 mercial Organic Analysis ” appeared, would now be regarded as outside the pale. This is evident from the following facts. In the United States Pharmacopmia of 1885, 6 per cent. of impurity was permitted in cream of tartar, but in the edition of 1890 the standard of purity was raised to 99 per cent., as ascertained by titrating the solution of the original sample with standard alkali, using phenolphthalein as the indicator. The German and Japanese Pharmacopceias also fix the standard of purity for cream of tartar at 99 per cent.I n 1888 (Pharm. Jour. [3], xviii., 1045) Messrs. Southall Brothers and Barclay published the results of the assay by Mr. R. A. Cripps, by the British Pharmacopoeia process, of sixty-eight samples of commercial cream of tartar. Of these, seventeen were found to answer the requirements of the British Pharmacopaia, but almost with- out exception a sample taken after grinding the bulk gave a lower result than a sample taken from the top of a cask, as is done when sampled by a broker. Of the casks the samples from which answered the British Pharmacopmia test twelve were pur- chased, but the contents of these when powdered reached the official standard in three cases only.I n a paper read before the British Pharmaceutical Conference at Leeas in 1890, Mr. H. Broadbent gave the following figures obtained by the analysis of cream of tartar :- Italian. French. German. Number of samples contributing to average ... 40 6 6 Average percentage composition :- Acid potassium tartrate ... ... ... 94-11 93.00 93.05 Neutral potassium tartrate ... ... 1-59 1.73 1 45 Calcium tartrate ... ... ... ... 4.02 4.78 5.00 Insoluble matter ... ... ... ... 0.23 0.28 0.25 Moisture ... ... ... ... ... 0.27 0-30 0.32 The majority of those who took part in the discussion of Mr. Broadbent’s paper were of opinion that the British Pharmacopoeia requirement of 92-15 per cent. on the moisture-free article was not too high.I n a paper read by Mr. T. A. Ellwood in 1891 (Pl~arm. Jour. [3], xxii., 392), he stated that he had never found more than 6.5 per cent. of calcium tartrate in cream of tartar, and was of opinion that the Pharmacopceia might advantageously limit the amount of this impurity to 4 per cent. I n a protest against this suggestion (ibid., page 448) Mr. R. A. Cripps quoted the results obtained by him in 1888 and already mentioned. Quite recently Mr. M. Conroy has expressed the opinion that the British Phar- macopoeia standard should be raised to at least 96 per cent., and Messrs. Kirkpatrick, Barr and Guthrie, a leading firm of importers, who were the first to raise the trade- test to 95 per cent. independent of the British Pharmacopceia, express the opinion that the standard shonld be raised to 99 to 100 per cent., as in other countries (Pharm.Jour. 141, ii., 346, 420). I t is evident, therefore, that it is very generally considered that the existing British Pharmacopoeia standard of purity is quite low enough, and that there is no178 THE ANALYST. excuse for the sale, under the name of cream of tartar, of such an article as formed the subject of the recent proceedings at Belfast. Of late years a good deal of cream of tartar has appeared on the market which has been prepared by 5t method essentially different from that hitherto considered. I t appears to have been produced under one of the modifications of the patent of A. Martignier (No. 20,078, of 1889). According to this process, neutralized wine-lees are treated with an excess of a saturated solution of potassiuni sulphate, whereby calcium sulphate and neutral potassium tartrate are formed. The gypsum is separated, and the solution of potassium tartrate decolorized with animal charcoal and treated with sulphuric acid in quantity sufficient for the reaction :- 2K,T-+ H,SO, = K,SO, + 2KHT.I t is evident that an article manufactured in this manner will be free from calcium tartrate, but will be liable to contain sulphates of potassium and calcium. I n fact, much of the creain of tartar of commerce now contains several units per cent. of calcium sulphate, just as an article made in the old way contained more or less calcium tartrate as a normal impurity. Both impurities are perfectly neutral, useless and harmless, so far as the consumer is concerned, but with a little trouble they both could, and would, be removed, if the present British Pharizlacopceia test were raised to the standard adopted in some other countries.I made a very complete examination some years since of a sample of cream of tartar prepared by the sulphuric acid process, and which yielded no trace of free sulphuric and tartaric acid to alcohol. I adopted the following line of reasoning as to the normal constituents of cream of tartar. The acidity of the sample may be due to :- a. Potassium acid tartrate, KH'I'. b. Potassium acid sulphate, KHSO,. c. Calcium tartrate, CaT. d. Potassium sulphate, K,SO,. e. Calcium sulphate, CaSO,. f. Neutral potassium tartrate, K,T The neutral salts which may possibly be present are : Of course, no neutral potassium tartrate can possibly be present in an article crystallized froni water containing sulphuric acid, and I very much doubt its occur- rence in creani of tartar manufactured by the old process. On ignition, the following changes would occur :- (a) KHT would yield K,CO, in amount just corresponding with the original tartrate ; so that one gramme of ignited KHT would exactly neutralize one gramme of unignited KHT.( b ) Any acid sulphate of potassium would react with the K,CO, thus :- SKHSO, + K,CO, = 2K,SO, + H,O + CO,. I n practice this would occur during the ignition. Any K,SO, produced is neutral, and hence any KHSO, originally present will reduce the alkalinity of the ash. It does this not only by not yielding alkalinity itself, as KHT would do, but also by neutralizing an equivalent ainountTHE ANALYST. 179 of K,CO, from the tartrate.Hence, if a sample contained KHT and KHSO, in equivalent proportions, on ignition it would give only K2S0,, and the ash would not be alkaline. Only trifling quantities of acid sulphate of potassium are likely to occur as a normal impurity in cream of tartar. (c) CaT on ignition yields CaCO,, and hence the ignited sample will neutralize a proportionate quantity of acid. But CaCO, being nearly insoluble in aqueous liquids, the portion of the ash soluble in water will be deficient in acid-neutralizing power as the CaT increases. But if the insoluble ash be included in the titration, the neutralizing power will exceed the acidity of the original sample.( d ) K,SO, is not affected by ignition, and hence may be left out of consideration. ( e ) CaSO, is not affected by ignition, but will react with the K,C03 (derived from the KHT) thus :- CaSO, + K2COtI = CaCO, + K,SO,. Hence calcium sulphate will reduce the alkalinity of the aqueous solution of the ash (and so cause a low British Pharmacopaeia test), but the acid-neutralizing power of the total ash will not be affected. (f) K2T will burn to K,C03, and the ash will have a higher neutralizing power than that yielded by an equal weight of KHT. From these considerations it follows that if a sample of cream of tartar be free from uncombined sulphuric and tartaric acids, and contains only calcium and neutral potassium sulphates and potassium acid tartrate, it will before ignition neutralize a volume of standard alkali exactly equivalent to the acid required to neutralize the sample after ignition, including the alkalinity of the insoluble ash.I f KHSO, be present, ihe acidity of the original sample will be in excess of the total alkalinity of the ash. If Ca? be present, the acidity of the sample will be less than the alkalinity (total) of the ash. As KHSO, and CaT are incompatible in solution, both impurities cannot be present in the same sample of genuine cream of tartar. I n an article prepared by crystallization from water, and subsequently adulterated with KHSO, (which has been actually used as a substitute for cream of tartar, under the name of A sample containing neutral potassium tartrate would yield on ignition an ash having a greater acid-neutralizing power than the acidity of the original cream of tartar.It is evident that when applied to samples of cream of tartar containing calcium sulphate, the existing British Pharmacopaeia test will indicate a proportion of acid potassium tartrate materially below the truth. Every unit of (anhydrous) calcium tartrate present will reduce the indication of acid potassium tartrate by 2.77 per cent., so that a sample containing only 4 per cent. of CaSO, will show by the British Pharmacopoeia method only 88.92 per cent. of acid tartrate. Such a result is manifestly intolerable, and it is to be hoped that the next edition of the British Pharmacopoeia will abolish this anomaly, and place the tests for cream of tartar on a level with those adopted in other countries. I may say that I have communicated with Dr.tartaline”), the two salts might co-occur.* * As acid potassium sulphate is deliquescent, its presence in cream of tartar as an intentional On the other hand, I have found notable traces in an article prepared by the adulterant is improbable. acid process.THE ANALYST. Attfield on the subject, but he declined to furnish any indication of what might be expected, though in his own practice he favours direct titration. It is, of course, important that the Pharmacopaeia methods should be as simple as possible, but the existing test for cream of tartar scarcely complies with this requirement. A direct titration of the original sample with standard caustic alkali and phenolphthalein would be preferable in every respect, if adulteration by acid potassium sulphate were prevented by fixing a limit to the amount of sulphates admissible.Where further inforination is required, it is readily obtainable by noting the acid-neutralizing power of the soluble and insoluble ash, and comparing them with the acidity of the original sample as already described. For this purpose I would propose the following process :- 1. Dissolve 1.881 gramrnes of the moisture-free sample in hot water and titrate with decinormal caustic alkali and phenolphthalein. In the absence of acid potassium sulphate (and of free tartaric acid), each C.C. of alkali required represents 1 per cent. of acid potassium tartrate in the sample. 2. Ignite 1.881 grammes of the moisture-free sample at a dull red heat for ten minutes, without attempting to burn off all the carbon.Boil the product with water, filter, and wash the insoluble carbonaceous residue. (a) Titrate the filtrate with decinormal hydrochloric acid and methyl-orange. In a pure sample the measure of acid required will be exactly equal to that of the alkali consumed in process 1. Each C.C. of deficiency represents 0.50 per cent. of calcium tartrate, CaC,H,O,; 0.36 per cent. of calcium sulphate, CaSO, ; or 0.60 per cent. of neutral potassium tartrate. Any cxccss points to the presence of acid potassium sulphate KHSO,, each C.C. of diflerence representing 0.71 per cent. of that salt. If the titrated liquid be treated with barium chloride, the weight of the precipitate of barium sulphate obtained will give the means of directly determining the proportion of calcium or potassium sulphate, and of deducing the calcium tartrate. ( b ) Ignite the carbonaceous residue, dissolve in 20 C.C.of decinormal acid, filter if necessary from any insoluble residue of sand, barium sulphate, etc., wash, and titrate the filtrate with decinormal alkali and methyl-orange. The measure required represents the calciuiii of the sample. Each C.C. corresponds to 0.50 per cent. of calcium tartrate, or 0.36 per cent. of calcium sulphate (anhydrous). The quantity of cream of tartar directed to be employed in the foregoing process is somewhat smaller than is desirable. Hence, in cases of importance, it would be preferable to operate on a double quantity, that is 3.762 grammes.Of course, the percentages of constituents corresponding to each C.C. of decinormal acid and alkali would, in this case, be one-half of the amounts stated above. In the above process, I have followed the direction of the British Pharmacopceia to operate on the moisture-free sample, but in practice it would be easier to analyse the original sample, and determine the moisture on a separate portion, making any allowance that might be necessary, I n exceptional cases, it may be necessary to examine cream of tartar by deter- mining the total tartaric acid, but the analysis of such samples is outside the scope of this paper.THE ANALYST. 181 DISCUSSION. The PRESIDENT said that some years ago he had analysed a large number of samples of commercial cream of tartar, and had found that as a rule they contained from 89 to 92 per cent.of the pure salt, as tested by their acidity. He was a little at a loss to understand how a sample of cream of tartar could normally contain potassium bisulphate. It seemed to him that the presence of both bisulphate and bitartrate would give rise to the presence of free tartaric acid. It appeared to be a matter of discusfiion whether a sample of genuine cream of tartar really could contain any sulphuric acid in the form of a bisulphate. Sulphate of lime used to be commonly found in samples of cream of tartar, and also very conimonly barium compounds in small quantities. These barium compounds were in an absolutely insoluble form, but in such small quantities that it was difficult t o imagine them to have been added intentionally.He was very glad to hear that pure, or almost pure, bitartrate of potassium wa6 an article of commerce. It was not very many years ago that he had experienced very great difficulty in getting a single pound prepared containing, say, 97 per cent. of real bitartrate of potassium. Sir CHAS. A. CAMERON said that the specimen referred to by Mr. Allen was the worst specimen of cream of tartar on sale in Ireland that he had ever examined. A great many samples had been examined in his laboratory, and the general average was fairly good. He might say, he was rather surprised that a member of his own profession should regard as commercially pure an article of which nearly one-fifth consisted of a foreign ingredient.Since the publication in the Belfast papers of the correspondence referred to, several manufacturers had written to him, sending samples of cream of tartar, and stating that they had for a considerable time been putting on the market an article containing 96 per cent. of pure cream of tartar. Dr. DYER said he had examined a great many samples of cream of tartar, and it was quite a common thing for them to contain 96 per cent. and more of the pure article. Samples of such high quality always contained sulphate of potash, and were generally quite free from lime. He had often heard complaints of darkening taking place in cream of tartar. This generally occurred in samples made by the sulphate process, and was evidently due to traces of iron forming traces of sulphide when, through organic decomposition, the sulphates became ’‘ reduced.” He would like to ask Mr. Allen whether he had had any experience of the going bad of cream of tartar by clogging and forming lumps. On several occasions samples had been submitted to hini of cream of tartar which had arrived after a voyage to Australia in this condition, and he had invariably found an enormous quantity of fungus running completely through the material and matting it together. The per- centage of moisture was usually small, and it would be interesting to know what were the actual circumstances in packing or storing that determined this free fiingoid growth, Mr. HEHNER suggested that the presence of barium compounds might possibly be accounted for in the following way : All Southern wines used to be very heavily He remembered two samples which contained 98 per cent.182 THE ANALYST.plastered, which converted the acid potassium tartrate into calcium tartrate and potassium sulphate. This was done partly because the colour of the wine was thereby heightened, and partly because the precipitate of calcium tartrate carried down any suspended impurities along with it, leaving the wine clear. Excessive plastering, however, and the consequent presence of a large amount of potassium sulphate in solution, were said to have very baneful effects, and several processes had been devised with the object of converting the potassium sulphate into potassium tartrate again. This was generally effected by means of barium tartrate, or barium hydrate and tartaric acid, the result being the re-formation of the acid potassium tartrate, together with a precipitate of barium sulphate. An edict had now been passed in France regulating the practice of plastering, and limiting the proportion of sulphates to 2 grammes per litre, calculated as K,SO,.Mr, ALLEN said that if barium sulphate was in any way a natural constituent of creatn of tartar, it would certainly be present in an amorphous form. It had, how- ever, been found in the form of crystallized heavy spar, which clearly showed that it had been fraudulently added. Besides, for gome years past it had entirely dis- appeared. With regard to the acid sulphate of potassium, he agreed with the President that it was a very unlikely constituent of cream of tartar, in notable quantity, unless purposely added. I t had, however, been used as a substitute for cream of tartar under the name of tartaline, so that its occurrence as an adulterant of that material seemed not altogether impossible. I t was known that fungoid growths were liable to develop in cream of tartar, but he had always imagined this to be due to excess of moisture. The low percentage of moisture in the cases referred to by Dr. Dyer negatived such a conclusion in this instance, and he was quite unable to offer any other explanation of the phenomenon. He had in his possession a letter, written as long ago as in 1893, stating that there were five factories in America turning out weekly, in the aggregate, 200 tons of bitartrate containing 99 to 100 per cent. of the pure salt, which was good evidence that it could be obtained on a large scale. But there was no encouragement for manufacturers to place a superior article on the market, while the British Pharma- copceia requirement was so much below that of other countries and the official test in certain cases gave a result materially below the truth.

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DOI:10.1039/AN8962100174

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年代:1896

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182 THE ANALYST. DETERMINATION OF LACTOSE IN MILKS BY DOUBLE DILUTION AND POLARIZATION. H. W. WILEY AND E. E. EWELL. IN vol. vi., p. 289, of the American Chemical JownaZ, one of us (Wiley) published an article on the determination of lactose in milks by optical methods. The principal novelty in this process was the substitution of mercuric nitrate as the reagent for precipitating proteids in place of the other reagents which had usually been employed for that purpose. By the use of mercuric nitrate in an acid solution, it was shownTHE ANALYST. 183 in that paper that it was possible to practically throw out all of the proteids dissolved in the milk. Inasmuch as these soluble proteids are optically active, and deflect the plane of polarization in a direction opposite to that produced by lactose, the presence of any notable quantity of them in the solution to be polarized tends to diminish the apparent percentage of lactose present.The reagent proposed, viz., acid mercuric nitrate, when used in the cold and in the quantities specified, produces no inversion effect whatever upon the lactose. I n the paper referred to, an arbitrary correction was made for the volume of the precipitate produced, and this was fixed at 2-5 c.c., when approximately 60 C.C. of milk were used in a 100 C.C. flask. This method of estimating lactose, on account of the ease with which it can be operated and its accuracy, has been generally adopted by chemists. Attention has been called, however, to the fact that the arbitrary correction allowed for the volume of the precipitate is too small, Theoretically, it is evident also that the arbitrary correction admitted is too small except in cases of well-skimmed milk. In order to eliminate this arbitrary factor from the method, we undertook a series of experiments to determine the actual percentage of sugar and the proper correction to be allowed for the volume of the precipitate by the method of double dilution and polarization originally proposed by Scheibler for sugar solutions, and suggested by Bigelow and McElroy for use in the polarization of milk sugar.(Journal of the American Chemical Society, xv., 694.) The results of our determinations are extremely satisfactory, and show that the volume which is occupied by the precipitate in a milk varies from 2.5 C.C.in the circumstances mentioned above, to 6 c.c., according to the richness of the milk in fat. It' appears, however, that this correction is less in quantity than the combined volume of the fat and albuminoids, which may be safely assunied to be 1 C.C. for 1 granime. All the flasks which were employed in the determinations were carefully calibrated, and the instrument used was the new triple-field shadow polariscope, made by Schmidt and Haensch, which enables readings to be accurately made to within 0.05 of 1 per cent. All readings were made in duplicate by each of us and entered hefore com- parisons were made, and in the polarizations given in the table the means of these four readings, which never differed by more than one-tenth of 1 per cent., are given. The polarizations were made on the contents of a 100 and a 200 C.C.flask, after clarification of the milk by means of acid mercuric nitrate. I n each case, double the quantity of the normal weight of milk for the instrument used was taken. The readings were calculated by the formula given by Scheibler, which requires that the reading obtained from the solution in the large flask be multiplied by 2 and subtracted from the reading obtained in the small flask. I n all cases, in order to secure greater accuracy, our readings were made in a tube 400 rnillimetres in length, Therefore the data obtained in reading the solution in the small flask were divided by 4 in order to obtain the apparent percentage of sucrose. The application of the formula given by Scheibler does not give absolutely accurate results.The true polarization in any given case is calculated according to the following scheme : Let x equal the volume of the precipitate and y the correct reading. Let a equal (See ANALYST, vol. xii., p. 64; vol. xx., p. 126.)184 THE ANALYST. the reading obtained from the solution in the small flask and b equal the reading of the solution from the large flask. We then have : 200-z : 100-x : : a : b 300 b-bx=100 a-ax az-bx=lOO a-200 b x=100 ( a - 2 b) (1) -- a - b 100-z : 100 : : w : a 100 ( a -‘(a - 2 b) = 100 y y=a- ( a - 2 b ) -4 a - b U LZ - b (21 a2-ab-a2+2 ab ab -- l j = - U - b a - b The rule derived from formula No. 2 is as follows : The true polarization, as determined by double dilution, is found by dividing the product of the two readings made from the solutions in the large and small flasks by their difference.I n order to test the accuracy of the method, known volumes of insoluble material, as, for instance, quartz sand, were added to the flasks in order that the volume of the precipitate might be increased by a certain definite amount. The determinations were also made on the whole milk as purchased, on the same milk deprived of the most of its cream, and on the cream thus secured. I n all cases the results obtained were satisfactory. Blyth has recently described a method of precipitating the casein with acetic acid, and of washing the precipitate free from sugar on a filter, and polarizing the filtrate (ANALYST, vol. xx., p. 122). The percentage of milk-sugar in the mixed filtrate and washings is about one and the polariscopic reading should be corrected for that degree of solution.This method evidently is better suited for preparing milk whey for the gravimetric estimation of the sugar by copper, since it takes no account of the albumins left in solution, which serve to a certain extent to counteract the polarizing power of the lactose. I n the presence of sucrose he proposed to estimate its quantity from the property possessed by citric acid of inverting the sucrose and leaving the lactose unchanged. Raumer and Spiith (Zeit. Angezo. Chcm., 1896, p. 72) suggest that the polarization of milk should be preceded by boiling, since it is probable that the lactose may exhibit birotation. The data which they adduce, however, are far from con- vincing, since, after the boiling, they clear the mixture with lead subacetate, and i t has been shown that this reagent does not remove all the proteids.The deficit in rotation is therefore probably due to the residual soluble left-handed proteids. They further suggest that the presence of a dextrinoid body, as indicated by Ritthausen (Joziriz. Prakt. Chem., ( 2 ) , xv. 348) may serve to increase the actual rotation of theTHE ANALYST. 185 1 2 3 4 5 6 7 8 9 10 11 12 13 milk-sugar. I n the samples which showed the apparent increase, however, they made no attempt to prove the presence of the alleged disturbing dextrin. There seems to be no just reason, therefore, for insisting on the slow and tedious gravimetric method when a quick and accurate optical method is at hand.Inasmuch as the time required for carrying out the method of double dilution and polarization is scarcely any longer than that required for a single polarization, it is recommended that it be done in all cases, instead of correcting the results of a, single polarization by any arbitrary factor. When the determination is conducted as suggested the analyst has at hand an easy, rapid, and accurate method of estimating milk-sugar in milk, which is as desirable in all respects as any gravimetric method whatever. The data obtained are given in the accompanying table. 2.9 4.8 3-1 4.0 1.4 5.5 4.4 2.0 17.6 POLARIZATION OF MILK BY DOUBLE DILUTION. No. Per cent. ~ Fat. Polarization in 200 C.C. Flask. 9.37 9.59 9-36 9 -60 10.15 10.31 9.49 10.01 9.44 11-05 9.57 9.75 8.72 Polarization in 100 C.C.Flask. 19.26 20.33 19-20 20.25 20.84 21 -21 19-41 2045 19-26 22-68 19.47 19-93 19-13 Apparent per cent. Lactose. 4-82 5.08 4.80 5-06 5.21 5.30 4.85 5.11 4.82 5-67 4.87 4.98 4.78 True per cent. Lactose. 4-56 4-54 4.57 4.56 4.95 5-00 4-64 4.90 4-63 5.38 4-71 4.77 4.01 True volume in 100 C.C. Flask. 94.4 88.8 95-0 89.7 94.8 94.5 95.7 95.9 96.1 94.8 96.5 95.8 82.4 Volume of Precipitate. With 5 C.C. quartz sand. Without sand. Without sand. With 5 C.C. quartz sand. Same as No. 8, after separation of cream. 5- Same as No. 6 , after separation of cream. 7 Whole milk. 8 Skimmed milk. Cream. Summary of AIethod.--For the scale of the instrument used, 32.91 grammes of pure lactose in 100 C.C. give a reading of 100. This number is derived from the following data : For sucrose, concentration 26 grammes in 100 c.c., [a]:'" = 66.37.For lactose, 33 grammes in 100 c.c., [a] ro = 52.53 ; then 66-37 : 52.53 :: x : 26.048 ; whence, x = 32.91. The temperature of the working room should be kept at about 20" C., since the rotatory power of lactose rapidly diminishes as the temperature rises. Double this quantity, viz., 65.82 grammes of milk, is placed in a 100 C.C. flask, clarified with mercuric nitrate solution, the volume completed to the mark, the contents of the flask well shaken, poured upon a filter, and the filtrate polarized in a 400 mm. tube. A similar quantity of the milk is placed in a 200 C.C. flask, and subjected to the same treatment. The polarimetric data obtained are used for calculating the true volume of the liquid in the flask, the true percentage of lactoseTHE ANALYST.and the true volume occupied by the precipitate, in accordance with the rule already given. Dissolve mercury in double its weight of nitric acid, specific gravity 1-42, and add to the solution five volumes of water. This solution is more dilute than the one recominended in the original paper, it having been noticed that a stronger solution colours the precipitated proteid matter slightly yellow (xanthoproteic reaction). Ten C.C. of the reagent are to be employed instead of two, as directed for the stronger solution. In preparing the solution of niilk in the 200 C.C. flask, it may be necessary at times to use more than this quantity of the acid mercuric nitrate, in order to secure a filtrate entirely free of turbidity. An inspection of the data in the table shows a general agreement between the volume of the precipitate found and the percentage of fat in the sample, with the exception of one instance, viz., No. 11. It is evident that in solutions so dilute a slight variation in the volume has a very small influence on the percentage of sugar found. An error of 0.05' in the reading of the dilute solution (200 C.C. flask) makes an error of 0.05 per cent. in the result. The error due to 1 C.C. of the precipitate in the dilute solution is approximately 0-05 per cent. I t is therefore evident that with proper care the percentage of sugar can be determined to within one-tenth of 1 per cent. by t,he polariinetric method, and this is entirely sufficient for all practical purposes. The acid mercuric nitrate solution is prepared as follows : CHEMICAL LABORATORY OF THE UKITED STATES DEPARTXENT OF AGRICULTURE.

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DOI:10.1039/AN8962100182

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年代:1896

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186 THE ANALYST. OFFICIAL METHODS FOR THE ANALYSIS OF FERTILIZERS, ISSUED BY THE GERMAN MANURE MANUFACTURERS’ ASSOCIATION, HARZBURG, MAY 28, 1895. CONTXIBUTED BY H. H. B. SHEPHERD, F.I.C., ANGLO-CONTINENTAL GUANO WOEKS, LONDON. (Coiztinuedfrom p . 156.) D. Water Determination.-In inuriate of potash and similar salts the water is determined by heating 10 grammes of the sample in a covered crucible to a, dull-red heat for about ten minutes. I n the case of salts rich in magnesia, the error due to the decomposition of the magnesium chloride by heat may be avoided by covering the weighed portion in the crucible with a layer of thoroughly burnt lime; or, the chlorine may be determined by titration before and after heating, and the necessary correction made, taking, of course, into account its replacement by oxygen.Appendix to Section IV.-(l) Preparation of Platiizic Chloride from the Alcoholic Washings and Precipitates from Potash Determinations.-The alcoholic washings, diluted with about one-third water, are boiled in a large porcelain basin on the water- bath with sodium carbonate, the potassium platinum chloride precipitates being added a little at a time. The evaporation is continued until the liquid standing over the reduced platinum becomes quite clear and almost colourless. The liquid is then poured off and the reduced platinum purified by boiling with hydrochloric acid and water, after which it is dried and then ignited, to get rid of organic matter. TheTHE ANALYST, 187 platinum-black thus obtained is, before dissolving, rubbed to a fine powder and boiled once with pure concentrated nitric acid, the nitric acid being poured away.Its solution is effected by heating in a large porcelain basin on the water-bath with four times its weight of hydrochloric acid, and adding nitric acid by degrees, in the proportion of 1 part nitric acid to 4 parts hydrochloric acid. When it has com- pletely dissolved, the solution is evaporated until a drop taken out on the end of a, glass rod crystallizes. The resulting platinic chloride, which forms into a cakg on cooling, is dissolved in water, the solution filtered and adjusted by addition of water so that 10 C.C. of the solution shall contain 1 gramme of metallic platinum (specific gravity 1.18). Special care must be taken that the solution contains neither platinous chloride nor nitrogen oxides.Any platinous chloride can be converted into platinic chloride by treatment with fuming hydrochloric acid and a little nitric acid, and nitrogen compounds can be expelled by alternate evaporations with hydrochloric acid and water. If scrap platinum is used for making the solution, the platinic chloride will be contaminated with a little iridium. This can, however, be separated by precipitating the platinum with ammonium chloride, and then re- ducing it to the metallic state. The purity of the solution can be most conveniently tested by means of an 80 per cent. muriate of potash sample of known composition, and prepared from pure materials. (2) Preparation of Barium Chloride Solution.-One hundred and twenty-two grammes of crystallized barium chloride are dissolved in water with 50 C.C.of con- centrated hydrochloric acid, and the solution made up to 1 litre. (3) AZcohoZ.-For washing the precipitate, alcohol of at least 96 per cent. must be used. (4) Filters.-Munktell Swedish filters, No. 1 F, are the most suitable for filtering off the potassium platinic chloride. V. Determinatioiz of Oxide of I r o n and Alamina in Phosphates.-The only method yielding serviceable results is Eugen Glaser's, modified by R. Jones.':: Ten grammes of substance are dissolved in 25 C.C. HNO,t of 1-2 specific gravity, and the solution made up to 500 C.C. Fifty C.C. of this solution (equal to 1 granime substance) are evaporated to 25 c.c., and mixed while still warm with 10 C.C. sulphuric acid (1 part concentrated H,SO, to 5 parts H,O).After stirring, 150 C.C. of alcohol are added, the mixture again stirred and allowed to stand for at least three hours. The calcium sulphate is then filtered off and washed with absolute alcohol, the filtrate being collected in an Erlenmeyer flask of 400 to 500 C.C. capacity. The washing must be continued until 10 drops diluted with an equal quantity of water give no red tint on addition of a drop of solution of methyl-orange. A small Bunsen pump may be usefully employed in the washing. The alcohol is now distilled off, tho liquid washed out into a beaker, made feebly alkaline with ammonia, and then heated until all excess of ammonia is expelled ; this is an important point, as other- wise the precipitate may contain magnesia.The precipitate is then collected upon a filter, using the ordinary rubber and cold water to remove any that may adhere to * Zeitschrift fur angewandte Chemie, 1889, p. 636. t The use of nitric acid as a solvent in the Glaser process results in the inclusion of iron pyrites as See paper by the Translator, ANALYST, vol. xviii., oxide of iron. This is contrary to the English usage. p. 261.-EDITOR.188 THE ANALYST. the sides of the beaker, and washed four times with boiling water, by pouring out of the mouthpiece of the wash-bottle, so as not to disturb the precipitate. In this way clear filtrates can always be obtained. If still greater accuracy is desired, Fresenius’s proposal may be adopted, which consists in adding some ammonium nitrate (of course not acid) to the wash-water.The precipitate is finally burnt off and weighed. I t is regarded as ferric phosphate and aluminic phosphate, and half its weight taken as oxide of iron and alumina, Should it be desired to weigh the calcium sulphate, it may be transferred while still moist to a platinum crucible, the filter-paper laid over it, the spirit burnt off, and the precipitate and paper ignited at a moderate tempera- ture until the weight remains constant. The calcined calcium sulphate is not too hygroscopic to prevent the use of an open crucible. It is not needful to resort to Jones’s modification, except in cases of dispute. The simple Glaser method, without the eva,poration of the phosphate solution or the washing of the calcium sulphate-merely filling up to the mark-gives sufficiently accurate results, and is much more rapidly carried out.VI. Nitrogen Deter.mination.-The methods we possess for the determination of nitrogen in its several forms are, on the whole, so accurate that discrepancies are easily avoided. (1) Nitric Nitrogen.-A number of processes have for years been known by which the old indirect method* of analysis of nitrate of soda can be replaced by the direct determination of the nitric nitrogen. These methods depend upon the raduction of the nitric acid by nascent hydrogen, and conversion of the nitrogen into ammonia. The first simple and reliable method was that of Ulach: 0.5 gramnie of the nitrate dissolved in 25 C.C. of water is placed in a flask with 5 gramnies of reduced iron and 10 grammes of dilute sulphuric acid of 1.35 specific gravity.I n the neck of the flask is hung a long pear-shaped glass bulb filled with cold water, which serves the double purpose of condensing the gases and preventing loss through spirting. The reaction coinmences at once in the cold, but after a little while the contents of the flask are cautiously warnled and finally raised to the boil. The reduction takes at the most ten minutes ; when it is finished, the glass bulb is carefully rinsed with the wash-bottle, about 150 C.C. of water and 25 C.C. of soda solution of 1-30 specific gravity added, the ammonia distilled off into standard acid, and the excess of acid determined by titrating back with soda, potash or baryta. The whole analysis can be performed in half an hour.I t is necessary to test the iron for nitrogen before use, as reduced iron frequently contains as much as 0.3 per cent. ; should any be present, the amount so introduced must be deducted from the result. Numerous modifications and improvements have been proposed which it is not necessary to enumerate. The method, however, of Devarda, which iE equally simple and quite reliable, can be very strongly recommended : 10 grammes of nitrate are dissolved in 1 litre of water and 50 C.C. of the solution (=Om5 gramme of substance) introduced into a flask of 9 litre capacity. To this are added 80 C.C. of water, 40 C.C. * It must here be remarked that the old indirect method for the analysis of nitrate of soda by determining the moisture and impurities, and taking the nitrate of soda by difference, is still the inter- national trade method, and is, therefore, retained by the import houses.THE ANALYST.189 of solution of soda of 1.3 specific gravity, 5 C.C. of alcohol, and 2-5 granimes of an alloy (in powder) consisting of 50 parts of copper, 45 parts of aluminium, and 5 parts of zinc. The flask is then at once connected with a condenser, and very cautioiisly and gently warmed to assist the reaction. I t takes about 20 or 25 minutes, and as soon as the disengagement of hydrogen ceases, the ammonia is distilled off. The alloy can be prepared by melting in a Hessian crucible 50 parts of copper, and adding first 45 parts of aluminium and then 5 parts of zinc to the molten mass. I t can, however, be purchased ready prepared from T. Srpeck, 62, Stumpergasse, Vienna, VI.I t is very brittle, and is easily pulverized. These two methods (Ulsch's and Devarda's) have taken the place of the older nitrometer method of Lunge," though the results obtained by the latter are quite satisfactory. The follow- ing is a description of this method : The nitrometer (see sketch) being firmly screwed in its holder, the tube 72 gf is raised, until the lower end is on a level with the three-way stopcock b. Mercury is then poured into the apparatus by means of a funnel, until the bulb c is completely filled and a little passes through the stopcock into a. The tap is now turned so as to shut off c, the tube 12 y f lowered, and about 0-360 gramme nitrate with 1 to 14 C.C. water introduced into the cup ct. The solution is allowed to flow into c, care being taken to prevent any air froin entering, and is followed by 15 C.C.of concentrated sul- phuric acid)(specific gravity 1.84). Gas is evolved at once, but after a time the part a c d c is cautiously shaken to assist the disengagement. The gas evolved forces the mercury into the bulb f and up the tube JL 9. The apparatus is allowed to stand for about an hour, and is then cool enough to read off. The tubes d c and h 9 are adjusted so that the mercury stands higher in 71 q than in d c by an amount corre- sponding to the pressure of the column of sulphuric in the latter (one division of mercury is equal to 7 divisions of sulphuric acid). The atmospheric temperature and pressure are then observed, and the volume of N,O, reduced to 0" C.and 760 nini. pressure. Each C.C. of N,O, corresponds to 0.003805 grammes of saltpetre. The nitrometer can also be used for the determination of nitrogen in mixtures of nitrate and superphosphate, only in this case it is more convenient to employ the original form of nitrometer, without the bulb c, as so much more substance is required to produce sufficient gas to fill the bulb. If this process is used, the substance can either be weighed direct, or a portion of the solution made for the determination of the soluble phosphoric acid can be taken. I n other respects, the process is carried out as above described. (2) dnzmoniacal Nitrogen.-20 grammes of substance are dissolved in 1 litre of water, and 50 C.C. (equal to 1 gramme), distilled with a 5 per cent.soda solution, or with thin milk of lime, until it is of the consistence of syrup. The method is carried out as follows : the 50 C.C. of solution are placed in a hard glass flask of about 600 C.C. or 700 C.C. capacity, 40 C.C. of soda solution of 1.3 specific gravity added, and the whole * Chcm. Industrie, 1881, p. 347. O190 THE ANALYST. diluted to 250 C.C. By means of a caoutchouc cork a Reitmeier's apparatus is then attached to the mouth of the flask. This apparatus consists of a glass bulb with two glass tubes blown on to it. The tube connecting the bulb with the flask, when the apparatus is attached, is short and straight, but that inside the bulb and connecting it with the condensation tube is bent. upwards. By this arrangement any spray that might pass over into the receiver is caught and returned to the flask.Tincture of cochineal makes the best indicator, as it admits of sufficiently sharp readings being obtained by gaslight. The method lately relied upon, viz., distillation with magnesia, is untrustworthy. Its introduction resulted in numerous discrepancies not before experienced, not only in the analysis of pure ammonia salts, but also of mixed manures containing nitrogen wholly in the form of sulphate of ammonia. The theoryupon which the process was based, viz., that by the ordinary soda distillation, some nitrogen, existing as organic compounds of ammonia salts, was converted into ammonia, proves to be erroneous, such compounds not occurring at all. Consequently, as it has been found to give rise to differences of as much as a half per cent.in the nitrogen with sulphate of ammonia samples, it is not for the present recommended. These differences would, however, disappear if the nitrogen sohble in water were determined, as in the case of the phosphoric acid. (3) Organic Nitrogen.-For the determination of nitrogen existing as organic matter and ammoniacal salts, the old method of combustion with soda-lime is in the first place applicable. A combustion tube of hard glass, 40 c.m. long and 10 mm. to 12 mm. wide, is closed at one end by drawing out to a point, and sufficient fine granular soda-lime introduced to occupy 4 c.111. to 5 c.m. from the end. The weighed portion, carefully mixed with soda-lime, is then passed into the tube, followed by some coarser soda-lime, leaving a few centimetres free at the mouth for the asbestos.The nitrogen bulb is then attached, and the combustion proceeded with. At first only the part containing the pure soda-lime is heated, but afterwards by degrees the whole tube, until gas ceases to come off. The point of the tube is then broken off and air sucked through the apparatus while it cools. The method introduced by Kjeldahl (Zeit. Anal. Chem., 22, 366) is, however, now generally used in place of the above. This method has been greatly modified and improved since it was first brought out, so that now indeed almost every laboratory has in use some special modification peculiar to itself. The Kjeldahl method is based upon the principle that nitrogenous compounds, on heating Tith concentrated sulphuric acid, in the presence of oxidizing agents, are converted into ammonia.One gramme of substance is introduced into a hard-glass flask of 300 C.C. to 400 C.C. capacity, 8 to 1 gramme mercuric oxide, and 15 C.C. concentrated sulphuric acid added, and the mixture heated-at first gently, afterwards strongly-until completely colourless. While being heated, the flask is supported upon wire gauze in an inclined position, and its mouth is closed by a loosely fitting long glass stopper, as a precaution against loss by spirting. A flask with a long neck answers the same purpose. After cooling, the fluid is washed out into a flask, and 150 C.C. of sodium hydrate solution of 30" BB., 25 grammes of a 10 per cent. potassium sulphide solution, and a few small pieces of zinc added, and the ammonia is then distilled off. I nTHE ANALYST.191 presence of nitrates this method cannot be used, as nitric nitrogen is only partly converted into ammonia. If & to 1 gramme of anhydrous copper sulphate is used in place of the mercuric oxide, the addition of the potassium sulphide is not required. The numerous modifications of this method are neither simpler nor more accurate than the above, and it is, therefore, unnecessary to describe them. (4) Total Nitrogen-For the determination of total nitrogen, i.e., organic, amnioniacal and nitric, we have two equally good methods, as follows : Jodlbauer's method. 1 gramme of substance is placed in a flask, and 50 C.C. of a solution of 20 grammes of phenol in 1 litre of concentrated sulphuric acid (66" B6) added.A combination takes place in a few minutes between the nitric acid present in the substance and the phenol, producing nitrophenol. Two to 3 grammes of zinc- powder (free from nitrogen) and & to 1 gramme of metallic mercury are then added, and the mixture boiled. I n from a half to three quarters of an hour the whole of the nitrogen compounds are transformed into ammonia, and amidophenol takes the place of nitrophenol. It is allowed to cool, some water cautiously added, allowed to cool again, an excess of sodium hydrate solution added and the ammonia distilled off. The weighed portion is placed in a 300 C.C. flask, and sufficient water added to bring it into a pasty consistence. From 1 to 4 grammes of reduced iron, and 5 to 10 C.C. of dilute sulphuric acid (1-35 sp. gr.), according to the approximate quantity of nitric nitrogen present, are added, and the mixture heated, as directed for Ulsch's method, until the evolution of gas ceases. Half a gramme of anhydrous cupric sulphate, and 15 C.C. of an acid solution containing 200 grammes phosphoric anhydride in 1 litre sulphuric acid are then added, and the mixture heated, very carefully at first, until a clear green liquid is obtained. Finally, the ammonia is distilled off in the usual way. This method is usually preferred to Jodlbauer's on the grounds of simplicity and rapidity of execution. The value of the sulphuric acid used for the absorption of the ammonia, is found by making repeated determination by precipit'ation with barium chloride. Kjeldahl's method combined with Ulsch's. (Coizcludecl.)

ISSN:0003-2654    

DOI:10.1039/AN8962100186

出版商:RSC    

年代:1896

数据来源: RSC

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THE ANALYST. 191 ABSTRACTS OF PAPERS PUBLISHED IN OTHER JOURNALS. TOXICOLOGICAL ANALYSIS. Estimation of Alkaloids by Titration with Iodine Solution. C. Kippen- berger. (Zed. anal. Chenz., 1896, xxxv., 10-27.)-1n his former paper (ANALYST, Abstracts, xx., 201) the author stated that, in titrating alkaloids with a solution of iodine in potassium iodide, in most cases the free iodine combined with the alkaloid to form the compound Alk.HI.1,. His later investigations show that the amount of potassium iodide has considerable influence on the results. Thus, when an iodine solution containing the smallest possible amount of potassium iodide was employed, more iodine was consumed than was the case in another series of experiments in which the iodine solution contained four times as much potassium iodide.On the other hand, the amount of iodine in the precipitate varied according to the quantity192 THE ANALYST, of iodine solution used. the reaction correctly described by the equation : With strychnine the theoretical two atoms of iodine are consumed if the potassium iodide is first added, and then an excess of iodine, but with narcotine and atropine the quantity taken up is always more than two atoms. The variations are explained by the theory that (1) the free iodine and water combine under the influence of the alkaloid superiodide; (2) that the hydriodic acid is partly oxidized to iodic acid; and that (3) iodine is again liberated and mechanic- ally retained by the superiodide precipitate. Hence, the author considers that only in certain cases is A1k.HCI + K I + I, = Alk.HI.1, + KCl. (1) 31, + 6HOH = 6HI + 3H,O,. (2) 6H1+ 3€I,O, = 5HI + HIO, + 3H,O. (3) HIO, + 5KI + 6HCl= 5KCl+ HCl + 31, + 3H,O. The fact that iodine could often be extracted from the precipitates by potassium iodide solution is urged in confirmation of this view. Where alkaloids other than strychnine are to be estimated, it is advisable to standardize the iodine solution with known quantities of the pure alkaloid, the con- ditions of the actual estimation being observed as far as possible. C. A. M.

ISSN:0003-2654    

DOI:10.1039/AN8962100191

出版商:RSC    

年代:1896

数据来源: RSC

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192 THE ANALYST, ORGANIC ANALYSIS. On Cold Saponification, 11. R. Henriques. (Zeit. angezu. Chem., 1896, 221-225.)-1n this communication the author describes further experiments on his method of cold saponification (,ANALYST, xxi., 67). A caution is given as to the preparation of the alcoholic soda, which must not contain any considerable amount of water, or it will not mix with the petroleum spirit. It is to be prepared by dissolving the alkali in 96 per cent. alcohol and filtering. The process has been tried on a large number of beeswaxes, the saponification number and acid value being determined in one operation. Three grammes of the wax were dissolved in 25 C.C. of warm petroleum benzine, and immediately titrated with seini-normal alcoholic soda, phenol-phthalein .being used as indicator.This gave the acid value. Twenty-five C.C. of normal alcoholic soda were then added, the whole warmed, and left for twenty-four hours in the cold, after which the excess of alkali was titrated. The ether value thus obtained, added to the acid value, gave the saponification number. The following results were obtained with five samples of pure beeswax : Acid Valne. Ether Value. Saponification No. Hiibl's Ratio. 1. Beeswax, yellow ... 20-6 ... 765-76-8 ... 96.6- 97-4 ... 3.72 2. 9 , 9 , ... 20.4 ... 72.9-73.9 ... 93.3- 94.3 ... 3.58 3. ), 8 , .. 20.6 ... 73-6-75.1 ... 94.2- 95.7 ... 3.6 4. ,, white ... 22.4 ... 76-1-76.9 ... 98.5- 99.3 ... 3-41 5. 3 , Y , ... 28.4 ... 76.6-77.1 ... 105.0--105*5 ... 2.71 The high figures given by the last sample are attributed by the author to a new method which had been employed for bleaching the wax.Waxes adulterated with cerasin and paraffin wax can also be readily saponified in this way, the experimentsTHE ANALYST. 193 described proving that no saponifiable matter is left undecomposed. The acid value and saponification number of three other substances used to adulterate beeswax were : Carnauba wax A ... ... 3.4 ... ... 78.4 78.4 83-4 220.0 131.4 Acid Value. Saponification No. I , ,, B ... ... 7.0 ... ... 83.4 Japan wax ... ... ... ... ... 221-2 Spermaceti ... ... ... 2.8 ... ... 130.6 Liver-oils gave results agreeing well with those obtained by the usual method of saponification, but with wool-fat constant figures could not be had. This is attributed to the soaps of wool-fat fatty acids decomposing in the presence of water more readily than the soaps of other acids.The substitution of alcoholic semi-normal hydrochloric acid for aqueous hydrochloric acid gave higher results, but still not always constant. Hence the author concludes that cold saponification, while applicable to all other fats and waxes, is not suitable for the class of wool-fats. Experiments on the saponification of various esters are described at length. For the most part they are readily saponified in the cold, but with acetates of the phenol series it is essential to have a considerable excess of alkali, or the results will be too low. C. A. M. Estimation of Caffeine by Means of Wanner's Reagent. M. Gomberg. (Jour. Amer. Chem. SOC., 1896, xviii., 331-342.ner's statement that caffeine (and one or two other alkaloids) is not prec by a solution of iodine in potassium iodide has hitherto been accepted witmout question. The author shows that this is only true of caffeine as a free alkaloid, and that when the addition of Wagner's reagent is either followed or preceded by the addition of dilute mineral acids, a dark-reddish precipitate, having the composition of CsHloN402.HI.14, i B obtained. When dry this periodide is a violet-blue amorphous powder, which melts at 213" C. The precipitation is quantitative, and the precipitate loses but little of its iodine when suspended in water. The method of estimation is substantially the same as that of Kippenberger (ANALYST, xx., 203), the acidulated solution of caffeine being precipitated by iodine solution, and an aliquot portion of the supernatant liquid titrated with decinorma 1 thiosulphate solution.The amount of alkaloid is calculated from the amount of iodine taken up by the formula : 41 : C,HloN,O, : : 506 : 194, i.e., one part of iodine represents 0.3834 parts of caffeine. the iodine was in considerable excess. strongly acidulated-about 1 C.C. of strong sulphuric acid to 50 C.C. of the liquid. large excem of acid, however, interfered with the reaction. The test experiments were very satisfactory, the best results being obtained when In every case the caffeine solution was A For the estimation of caffeine in drugs the following process is recommended :194 THE ANALYST. The drug is thoroughly digested in hot water, cooled, made up to definite volume, and filtered.An aliquot portion of the filtrate is treated with lead acetate, the precipitate allowed to settle and removed by filtration. The lead in the filtrate is removed by precipitation with sulphuretted hydrogen and filtration, and the filtrate, after boiling off the sulphuretted hydrogen, is divided into two portions. To each of these a definite volume of the standard iodine solution is added, the first without the addition of any mineral acid, the second with the addition of some hydrochloric or sulphuric acid. After standing five or ten minutes, the residual iodine in the solutions is estimated as described above. Since caffeine is not precipitated in neutral solutions or in presence of tolerably strong acetic acid, any absorption of iodine in the first portion is due to other materials in the drug.This must be subtracted from the amount of iodine taken up by the second portion; the difference represents the iodine used in the formation of the periodide of caffeine, This, multiplied by 0.3834, gives the amount of caffeine in the aliquot portion of liquid taken. The author considers that the experimental evidence on which the above method is based entirely contradicts Kippenberger's conclusions on the action of iodine solution on alkaloids (ANALYST, xx., 201, and preceding extract) ; and that, whatever the case may be with other alkaloids, his (Kippenberger's) theory as to the production of hydriodic acid from iodine and water does not hold good in the case of caffeine. C.A. M. Commercial Analysis of Glucose. V. Denamur. (Bzd1. de ~ ' , h s . be@ Chim., 1896, ix., 341-343.)-Twenty grammes of the sample are made up to 200 grammes with distilled water, the solution filtered, and the specific gravity taken at 17.5" C. The extract corresponding to this gravity in Balling's table multiplied by 10 gives the amount of solid matter in 100 grammes of the glucose. This figure subtracted from 100 gives the moisture. To determine the unfermentable portion, 100 granimes of the above solution are weighed into a tared Erlenmeyer flask, 1 or 2 gramrnes of pressed yeast added, the flask stopped with cotton-wool, well agitated, and incubated at 25" to 30" C. After fermentation the liquid is filtered, the flask washed out over the filter, and the filtrate replaced in the flask. The liquid is then evaporated to about 50 C.C. on a sand-bath, so as to completely expel the alcohol, and after cooling is again made up to 100 grammes. The specific gravity is then taken, and the corresponding figure in Balling's table multiplied by 10 gives the amount of solid non-fermentable matter in 100 gralnmes of glucose. The following results were obtained with four samples of glucose syrup : Moisture. Solid Matter. Unfermentable Solid Matter. Per cent. Per cent. Per cent. Syrup (I.) ... 21.523 78.477 30.970 (11.) ... 25.734 74.266 3 1 -060 (111.) ... 23.131 76-869 29.592 Very thick syrup ... 14.854 85.146 38-062 C. A. MI.

ISSN:0003-2654    

DOI:10.1039/AN8962100192

出版商:RSC    

年代:1896

数据来源: RSC

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THE ANALYST. 195 INORGANIC ANALYSIS. The Solution of Phosphates for Analysis. Henri Lasne. (Ann. de Chimie Analyt., i., 85-89.)-The methods of dissolving the phosphate proposed by different experimenters are selected chiefly with reference to their bearing on the subsequent operations, and the final results differ in each case on account of the varying pro- portions of gangue attacked by the solvents. I n selecting from among them the method which fulfils the greatest number of essential conditions, attention must chiefly be directed to the solubility of the silica, iron, alumina, and especially fluorine, present, because the phosphoric acid and protoxides are sure to be dissolved whichever process be employed. Most phosphates contain fluorides, and the hydrofluoric acid, liberated by the acid solvents, attacks the silica, in the gangue, bringing it into solution as silica and f-luosilicates, the presence of which is a cause of error in all the subsequent deter- minations.The fluorides should, therefore, be removed at the outset, and this is most conveniently effected-when volatile acids are being used-by evaporating to dryness, as in this case the fluoride of silicon is disengaged, and the silica remaining is rendered insoluble. The results will, however, differ according as the evaporation is effected in presence of the residue, or after the liquid has been separated therefrom. As a solvent for phosphates nitric acid, used alone, is unsuitable ; it attacks the ferric oxide with great difficulty, and leaves behind an unknown quantity of this substance--a circumstance sufficient to condemn it for general use. The action of dilute sulphuric acid is very slow, owing to the slow solubility of the calcium sulphate, This acid is therefore only suitable for such special cases as when the iron is to be estimated by permanganate.Under the action of concentrated boiling sulphuric acid, as a rule nothing remains in the washed residue but silica and alumina, and, whatever acid solvent is used, a good deal of the alumina will certainly be left unattacked, and have to be determined separately in a complete analysis. Generally, however, the investigation is confined to the alumina that has become dissolved and is capable of ' reducing ' the superphosphate. I n practice as small an amount as possible of acid of 50" B.(specific gravity, 1-532) is used, conse- quently the unaffected matter is in contact with free phosphoric acid and acid phosphate of lime, and not with concentrated boiling sulphuric acid. The varying action of the solvents on the alumina is shown in the accompanying table, the figures (which refer to the insoluble residzie, this being the most convenient for the estimation) being given in relation to phosphorus pentoxide =loo. I n the original crude phosphate the alumina amounted to 7.635 per cent. of P,O, : Alumina. Silica. ... ... ... ... Residue from superphosphate 0.805 11.940 Besidue from phosphate acted on by : 1. Concentrated boiling sulphuric acid ... 0.644 7.000 3. Aqua regia ... ... ... ... ... 1.065 7.910 5. Aqua regia ... ... 0.807 10.200 2.Hydrochloric acid, boiled for ten minutes 1.152 6.222 4. Hydrochloric acid, evaporated to dryness 0.895 10.250 ... ... ...196 THE ANALYST. This shows that the action of boiling concentrated sulphuric acid is too energetic, and that of the volatile acids is the reverse, the results obtained in practice being most nearly approached by employing the latter solvents and evaporating to dryness without removing the residue. I n order to render the silica completely insoluble the residue must be moistened and re-dried several times. It is then taken up with a minimum quantity-say 1 C.C. of 20" B. (specific gravity, 1.161) hydrochloric acid, and 20 C.C. of water per gramme of phosphate-maintained at a temperature of about 100" for at least half an hour, and filtered through a tared filter into a graduated glass, the liquid being afterwards made up to 100 C.C.per 1 gramme of phosphate ; or the liquid may be made up to the desired volume before filtering. The addition of nitric acid to the hydrochloric acid will destroy most, if not all, of the organic matter frequently present in crude phosphate, but it is perhaps better to use the latter acid alone, and to estimate approximately both the organic matter left in the residue and the small quantity that passes into solution. The evaporation is generally performed in a flat porcelain capsule over a sand- bath, avoiding heating the latter too strongly, but where the residue is small, or greater accuracy is required, a platinum dish must be used, in which case no nitric acid should be added.I t is sometimes useful to add a known quantity of silica, which is subsequently deducted from the weight of the residue. When higher oxides of manganese are present their action may be neutralized by a little oxalic or formic acid, or alcohol. If oxalic acid be used any excess in the solution must be neutralized. The estimations are made with aliquot parts of the hydrochloric acid solution, portions of which may, if desired, be transformed into nitrates or sulphates by evaporation in presence of an excess of the corresponding acids. c. s. Inaccuracies in the Estimation of Manganese in Ferro-Manganese. H. von Juptner. (Oestcrr. Zeits. Berg. ZL. Hiittenw., 1896, xliv., 15 ; through Chem. Zeit. Eep., 1896, 52.)-Although one cause of the want of agreement often shown in these analyses is due to the different atomic weights used in the calculations, the chief reason lies in the errors of standardizing the permanganate employed. Mohr's salt, ferrous ammonium sulphate with 6 molecules of water, is apt to contain ferric oxide, and it is also liable to lose ammonia in the presence of stronger bases. On exposure to air, it changes to a ferric ammonium sulphate with (theoretically) 3 molecules of water; but as more than this amount is given off during the action of the atmo- spheric oxygen, the crystals are liable to be dainp. The use of steel of known com- position is to be avoided, as some of the metal may become oxidized during solution in the acid, while the combined carbon is capable of reducing permanganate. Oxalic acid gives exact results and is the best substance to employ. F. H. L.

ISSN:0003-2654    

DOI:10.1039/AN8962100195

出版商:RSC    

年代:1896

数据来源: RSC