摘要:

THE ANALYST. AUGUST, 1887. PROGRESS OF THE BUTTERSUBSTITUTES BILL. THE following is from the Times Parliamentary report of 9th July :- The House went into Committee on this Bill. Mr. KENNY moved to substitute the word “oleomargarine” for the word “butterine.” Mr. JACOB BRIGHT moved to report progress. The motion was negatived. Mr. ILLINQWORTH objected to giving an article of commerce a bad name if it could be avoided. Mr. BIGQAR said that the bad name would be applied to an article made from lard, worth 4d. a pound, and sold as butter at the price of butter. Mr. JACOB BRIGHT said the evidence before the Committee was that butterine was a wholesome article, with which bad butter could not compete. Sir R. PAGET, having originally opposed the name butterine, would now retain it, and thought that the Bill in its present state would sufficiently carry out the object which they had in view.Mr. A. O’CONNOR, as representing an agricultural constituency, supported the amendment. Mr. RITCHIE opposed the amendment as unnecessary for the protection of purchasers. Dr. CLARK supported the adoption of the word (‘ margarine ” without “ oleo.” It was necessary to distinguish between that which came from the living cow, and that which WM made from the cow when it waa dead, and butterine did not sufficiently indicate the difference. Mr. ADDISON disputed the right of Parliament to fix names for articles of commerce. Mr. KENNY said that Parliament legislated against fraudulent trade-marks, and the name butterine had been adopted by the trade because its similarity to butter facilitated the deception of the public.The Committee divided, and the numbers were- For the amendment . . .. .. * b .. 87 Against .. .. .. .. .. .. 70 Majority . . .. .. .. -1 7 The word ‘‘ butterine” was, therefore, struck out. It was agreed to amend the amendment by substituting (‘ margarine ” for “ oleomargarine,” and, after a short con- versation, the word ‘‘ margarine ” was inserted. This involved several consequential amendments by the substitution of “ margarine ” for “ butterine.” Mr. JACOB BRIGHT moved to amend the penalties clause by taking away the option of imprisonment. Mr. KENNY said the Committee on the Bill, after full consideration, determined that imprisonment should be retained. Mr. ILLINGWORTH thought the money penalties would be sufficiently deterrent.Mr. MACLURE opposed imprisonment.144 THE ANALYST. Mr. F. 8. POWELL said there was a tendency in modern legislation to form new crimes. The clause put toomuchpower in the hands of mgktmtes. (Ironical cheers,) Under the Adulteration Acts imprisonment could not be ordered unlm the adulterant were injurious to health. After further conversation the amendment was agreed to, and the penalty of imprisonment was struck out. The provision that small quantities should be labelled ‘( butterine, not butter ” W ~ S altered to ‘6 margarine,” the words (( not butter ” being struck out. Mr. ADDISON moved the omission of Clause 4, embodying the description of the label to be used by retailers, which he criticised as needlessly minute.Several members said the description had been accepted by representatives of the trade, and others replied that the change of name from butterine to margarine had rendered unnecessary the stringent conditions that were accepted with a less objectionable name. Sir R. PAGET said the clause was essential to the Bill, and w&s really framed on the practice and suggestions of traders. The Committee divided, and the numbers were- (Ironical cheers.) For the clause . . .. .. .. .. ,. 106 Against .. .. .. .. .. . . 23 Majority . . * * .. .. --83 The clause was therefore retained. Mr. ADDISON move the omission of Chuse 6, which gives the right to inspect Sir R. PAGET said the clause was inserted at the request of the largest manufacturer The clause ww agreed to. The Bill passed through Committee. On 11th July, this Bill, as amended, was again considered. Mr. MACLURE moved to amend the title of the Bill by substituting “ butterine ” After some discusdon the House divided, and the numbers were- premises. of margarine. for (( margarine.’’ For the amendment . . .. .. 9 . .. 99 Against . * * . .. e . m e 124 After certain amendments had been agreed to, the Bill W&EI read a third time. Majority against . . .. .. -26 The word margarine thus Snally remains in the Bill.

ISSN:0003-2654    

DOI:10.1039/AN8871200143

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

144 THE ANALYST. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYST8 PEPPER. BY THOMAS STEVENSON. R d at the Meetimg, Jzune, 1887. THE following determinations may be of interest. The peppers were ground by myself; and 60 grms. of pepper were operated upon in each case. The ground samples were exhausted with hot methyhted spirit of wine, 60 O.P., an operation extending over several days.THE ANALYST. 145 The alcoholic liquids were evaporated, and the extracts digested with a cold solution of potash. The piperine thus separated was washed with water, dried at looo C., and weighed. It was then re-crystallised from alcohol, and reweighed in a high state of purity. The resin was obtained by precipitating the potash solution with hydrochloric d d , and was no doubt a mixture of resinous and oily bodies.The results are given in terms of air-dried pepper ; and each of the samples lost about 14 per cent. of its weight when dried in the water-oven. Piperine per cent. Resin per cent. Black pepper . . .. .. .. . . . . 7-14 1 *44 White pepper . I .. . . .. . . 6-47 0.63 Long pepper . . .. .. .. .. . . 4.34 1-16 Long pepper is inferior in pungency to black pepper ; but it is doubtful whether the contention that where ‘ I pepper ” only is asked for, and long pepper or a mixture of black and long peppers is supplied a fraud is committed, can be maintained. The term “pepper” was at one time undoubtedly applied to both round and long peppers; and it is only within recent years that long pepper has been removed by botanists from the genus p-pe~. I am clear, however, that if either “black” or “white” pepper be demanded, long pepper, or a mixture, ought not to be supplied. 99 (Trang) . .. . . .. . . 6.62 0.82

ISSN:0003-2654    

DOI:10.1039/AN8871200144

出版商:RSC    

年代:1887

数据来源: RSC

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THE ANALYST. 145 NOTES ON THE LOGWOOD TEST FOR ALUM IN BREAD, ETC. BY W. C. YOUNG, F.I.C., F.C.S. (Read at the Neeting, June, 1887.) IN my paper on this subject, read at the December meeting of last year, I assumed, from the results of experiments therein described, that the reaction with the logwood test was only obtained when the alumina was present in a form soluble in water ; and I stated my opinion that it was possible that under some circumstances no reaction would be obtained, even if alum had been added. In the course of the discussion it was pointed out that phosphate of alumina was insoluble in acetic acid, and that therefore my results could not be explained on the assumption that the alumina naturally present in the flour existed in the form of phosphate. To this I replied that it was possible that the alumina, in whatever form it existed, was combined with the gluten ; and this compound might, like gluten, be insoluble in water, and soluble in acetic acid.I have carried the investigation a little farther, and now beg to lay the results before you. With reference to the insolubility of phosphate of alumina in acetic acid, I find it is not so insoluble as is supposed ; for if to a weak solution of alum ZL drop of solution of phosphate of sodium is added, the precipitate formed is dissolved on the addition of acetic acid. Again, no precipitate is obtained by the addition of a drop of solution of phos- phate of sodium to a weak solution of alum acidified with acetic acid. In both instances the precipitate was immediately produced on warming the liquid, but again disappeared when the liquid was set aside in the cold for a few hours.It is therefore evident that phosphate of alumina is distinctly soluble in cold, and insoluble, or nearly so, in hot, acetic acid.146 THE ANALYST. As far as I have been able to ascertain, this peculiar property of phosphate of alumina has hitherto escaped notice? and it will at once be seen that it must affect the accuracy of such processes for the estimation of uhimina in bread, etc., as are based upon the insolubility of phosphate of alumina in acetic acid. I have a number of experiments in progress upon this point, tho results of which I hope to be able to bring before the Society at an early date. Having observed, m described in my former paper, that the addition of acetic acid to bread, which had previously given no reaction with the logwood test, had the effect of producing the blue colour in a very marked manner, I thought it possible, by soaking the bread in acetic acid, to dissolve out the alumina and leave the bread free from it; but I find by experiment that after repeated soakings (the bread being subsequently washed free from acid) the reaction is obtained on again acidifying, the successive acid solutions also giving a marked reaction with alkaline logwood solution.It is therefore evident that the alumina naturally present is so thoroughly diffused throughout the whole substance of the bread that it is almost impossible to extract it in this way. My next experiment was directed towards ascertaining whether pure wheat starch, or gluten, or both, contained alumina sufficient to produce a reaction after treat- ment with acetic acid.I found it extremely difficult to separate the last trace of gluten from the starch; but when I obtained the starch quite free from it I was unable to get the least change of colour with tho logwood reagent after treatment with acetic acid. On the other hand, every sample of gluten I prepared gave a marked reaction when treated in a similar manner. This result shows conclusively that the alumina is contained in the gluten, and is absent from the starch, and explains the difflculty experienced in endeavouring to dissolve the alumina out of bread, as above stated. Some doubt having been expressed as to whether phosphate of alumina had the =me property of fixing the logwood colour as the hydrate, I made the following experiments:- Two portions of a solution of alum were taken, each coloured with tincture of log- wood; to one a few drops of solution of ammonia were added, and to the other a few drops of solution of phosphate of soda.In both cases the colour was carried down with the precipitate. This experiment showed that immediately on. preci@tatiort both had the same pro- perty of fixing the colour, and on repeating the experiment, by adding the tincture of logwood after the precipitation of the hydrate and phosphate of alumina, I found that both precipitates extracted the colour. In order to itscertain whether these precipitates lost this property by keeping, I next prepared some hydrate and phosphate of alumina by precipitation, thoroughly washed the precipitates on filters, and set them aside for ten days j at the end of this time they were still in a gelatinous condition, but were apparently quite free from super- fluous moisture.I then suspended a portion of each in water and added alkaline log- wood solution, when I found that both still retained the property of mordaunts. * Bell, in his 66 The Chemistry of Foods,” part ii., p. 113, gives a modification of Dupr6’s process for estimation of alum in flour, etc., and states that he has found that the whole of the alumina is not precipitated in the cold, and that the remaining alumina could be recovered on boiling.TBE ANALYST. 147 I may here mention that the colour given with the phosphate appears much lighter than with the hydrate when seen by reflected light, which is, no doubt, due to the greater opacity of the former, as when seen by transmitted light the colours are identical.It would seem from the results of these experiments that if the alumina in bread were present in the form of free hydrate or phosphate, a reaction would always be given with the logwood test, and further, that it is necessary to get the alumina into one of those forms in order to obtain the blue stain ; therefore, I was not strictly correct in assuming in my former paper that the logmood test would fail, unless the alumina in tho bread was in a soluble form, although I still believe that practically it is always the case when the reaction is given. Another conclusion which may fairly be drawn from my results is that ths alumina naturally present in, flour is combined with the gluten. This being so, I thought it would be interesting to see if gluten would absorb alumina from a solution of alum.With this object I prepared some gluten, thoroughly dried it, and found the ash equal to 1-38 per cent. A portion of this gluten finely powdered was placed in a 2 per cent. solution of alum, and kept for some hours at a temperature of about 180°F. ; it was then thrown on to a filter, thoroughly washed, and dried. The ash then amounted to 1-32 per cent. Taking into consideration the great difficulty of washing tbe gluten free from excess of alum, I do not think this slight increase of ash is due to absorption of alumina. Although gluten does not appear to have the property of absorbing alumina Prom a solution of alum, yet its properties are affected in a marked degree by contact with such a solution, as i t may then be kept moist in a warm place without giving any indica- tion of decomposition, whilst ordinary gluten, as is well known, darkens in colour, swells, and rapidly decomposes undor similar circumstances, With reference to my former statement that the logwood test may fail, even if alum had been added to the bread, I have tested a large number of samples containing alum in different quantities, and made and baked in a variety of ways, and I am bound to say that in every case I have obtained it reaction, such as could not be in any way over- looked.

ISSN:0003-2654    

DOI:10.1039/AN8871200145

出版商:RSC    

年代:1887

数据来源: RSC

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TBE ANALYST. 147 QUANTITATIVE DETERMINATION OF PEPPER MIXTURES. BY A. W. STOKES, F.C.S., F.I.C. Bead at the Meeting, June, 1887. SEVERAL methods have been suggested for the estimation of mixtures of pepper with other substances, though none, 1 believe, has resulted in a quantitative formula. Thus, Mr. W. Blyth suggests that the nitrates and nitrites might form a guide; but as he finds they vary in genuine peppers from *038 to .118 per cent. (when calcu- lated as nitric acid) little reliance can be placed upon this for a quantitative method. The quantity of piperine has been proposed also as an index; but in genuine peppers, including long pepper, this varies from 1.7 to 9-38 per cent. Even in avariety148 THE ANALYST. of blackpepper samples the piperine ranges from 4 to 9-38 per cent.Nor is the estimation of piperine an easy and rapid operation. Mr. C. Heisch lays great stress upon the percentage of starch natural to pepper, stating that he would ‘‘ view with great suspicion ” a pepper containing less than 50 per cent. of starch. Yet his own analyses (THE ANALYST, vol. xi, p. 188) show a sample of genuine Acheen Penang containing only 48.53 per cent,, while a mixture of 90 per cent. of black pepper with 10 of Poivretteis shown to contain 49-98 per cent. of starch. In nine samples of black pepper, Mr. Heisch’s analyses show a variation from 48.5 to 56.6 per cent. of starch. In two samples of long pepper the starch is given as 46.1 and 68.9 per cent. Pepper-starch cannot be rapidly or easily estimated. For these reasons the quantity of starch found in a mixture would not well serve for quantitative purposes in fixing the amount of adulteration.The amount of ash is sufficient to show any abnormal proportion of sand and dirt ; but for admixture with olive-stones, rice, and starch generally, no quantitative method is known. In my opinion the determination of the woody-fibre will, as a rule, be sufficient for obtaining a very close approximation to the extent of admixture, In separating woody- fibre by the usual method of boiling the substance, first with acid, and then with alkali, constant results are difficult to obtain. The alkali always dissolves up part of the fibre ; how much, depends upon the fineness to which the substance is ground. From pepper mixtures, to obtain the woody-fibre, we have to get rid of starch, ash, piperine, and resinous bodies.This I find can best be done by taking, say 1 grm. of the sub- stance, boiling it in a flask for five minutes with 100 C.C. of distilled water. This swells out the starch granules. Now 50 C.C. of distilled water containing 6 C.C. of strong sul- phuric acid are added, and the whole is boiled for one hour under an upright condenser. The contents of the flask are then washed on to a weighed filter-paper, carefully washed with hot distilled water, then with hot alcohol, and lastly with ether. The filter-paper is placed in a weighing tube, dried, and weighed. Some allowance should be made for loss of weight of the filter-paper when extracted by hot sulphuric acid solution, alcohol, and ether. Filter-papers (English) of 541 inches diameter lost 0012 gramme when sub- mitted to this process.It is then incinerated, and the weight of the ash subtractedfrom the former weight. Thus determined, closely cmcordant percentages of fibre are ob- tained from the same sample. Taking a number of samples of the same peppers, etc. (for some of which I am in- debted to the kindness of Dr. T. Stevenson), I find the following percentages of fibre (in the dried samples). Black pepper 21-0 to 26.3 with an averago of 24.4 per cent. White ,, 12.7 to 13.8 ,, 9 , 13.3 9 , Long ,, 20.0 to 22.3 ,, 9 9 21.0 9 , Olive stones 62.2 to 64.2 ,, 9 , 62.6 ?9 Rice 0.8 to 1.6 ,, $ 9 1.0 9 , A more extended series of analyses might perhaps alter these averages slightly, but not, I think, materially.THE ANALYST.149 Accepting these averages as correct a general formula for calculating a mixture of olive stones with pepper would be lOOa - loom @-P Where n: = percentage of dry pepper. x = a = Y7 77 fibre in dryolive stones. m= 7 9 77 77 mixture. P = 17 9 9 7, Pepper. The formula for a mixture of black pepper and olive-stones would be for 6250 - 100% instance :- x = - - ~ - 38*l Mixtures of pepper with the above adulterants were made, and the fibre deter- A mixture of black pepper and olive stones containing :- mined. 10percent.oli~~estonesgave 28*6percent. fibre,usingformulagives 11.1 per cent. olive stones. 20 99 9, 33.8 7 7 7, 9 9 24-7 ), 7, 30 7 9 Y7 36.6 7 7 $9 9 , 32-1 ,, Y7 A mixture of white pepper and olive stones containing :- 10percent.olivestonesgave 18.4 percent, fibre, this formulagives 10.4 per cent.olive stones. 20 9, 9, 23'5 97 17 97 20-s ,, 1, 30 19 97 28.7 7, ,9 9 , 31-3 ,, 77 A mixture of long pepper and olive stones containing :-- 10 per cent. olivestonesgave 24.9 percent. fibre, this formulagives 9*4per cent. olive stones. 20 99 9, 29.0 7, 7 7 ?> 19.3 77 7 9 30 $ 9 97 33.3 97 9 7 97 32.1 ,, 9 7 A mixture of rice with white pepper containing :- 10 per cent. rice gave 11.9 per cent. of fibre, this by formula gives 11.3 per cent. of rice. 20 >7 22 11.0 7, 7 9 9 , 18.7 ,, 9 7 30 17 9 9 9.8 7 7 99 77 28-4 ,) ' 9 Rice is usually added only to white peppers, so that the formula in such case would 1330 - lOOm be Rice, per cent. = 12-3 I n the w e of mixtures of white and black peppers to which olive stones have been added,it is necessary to estimate by the appearance and by the ash the probable proportions of white and black present, and then to take as the percentage of fibre naturally present some number between 13.3 and 24.4 for the formula in calculating results. The result will necessarily be only approximate. Of course the presence of olive stones and of starch (foreign) should fht be discovered by the microscope before applying the quantitative method indicated. For mixtures of long pepper with other peppers the process is not applicable. I would here express my thanks to my assistant, Mr. E. Michael, for care and attontion in carrying out much of the above work. Conclusion of the Society's Proceedings.

ISSN:0003-2654    

DOI:10.1039/AN8871200147

出版商:RSC    

年代:1887

数据来源: RSC

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150 THE ANALYST. METHOD OF SEPARATION OF COLOURING MATTERS I N BUTTER, IMITATION BUTTER, AND SO-CALLED BUTTER COLOURS. BY PROF. ALBERT R. LEEDS, PH.D., Professor of Chemistry in Stevens Institute, Hoboken, N. J. IN the case of butter and imitation butter which contain minute quantities of colouring matters, 100 grams. of the sample are dissolved in 300 c.cm. of petroleum ether. The specific gravity of this ether, which I have myself used, has been 0.638. It evaporates completely, leaving no residue or trace of colour behind. A graduated cylinder or ‘‘ test- mixer ” can be advantageously used in making the solution. The ethereal solution of the fats and colouring matters is separated from the water and salts by means of zt separating funnel. It is washed with 100 c.cm. of water in successive portions, and these wash-waters are drawn off by the separating funnel.The ethereal solutions of tho fat are allowed to stand, in winter, in the cold, or surrounded by ice-cold water, for 16 or 20 hours, when a large quantity of stearin crystallises out. I n some cases the stoarin thus separated amounted to 20 per cent. of the total weight. The clear yellow ethereal solution, after being decanted from the separated stearin, is shaken up in the test-mixer with 50 c.cm. of a decinormal solution of potash. This is usually sufficient to dissolve out all the colouring matters which are capable of being dissolved by dilute alkali. After the aqueous solution of the colouring matters has been drawn off from the ethereal solution of the fats, this aqueous solution is very carefully acidified with dilute hydrochloric acid until just acid to test paper.The colouring matter (accompanied by a small amount of fatty acid, which unfortunately is always formed by the saponification of the fats and subsequent setting free by the acid) then separates out. It is filtered through a tared filter and washed with cold water. I n one experiment, in which only 50 grams. of oleomargarine were thus treated, the colouring matter and some fatty acid accompanying it weighed 0.145 gram. It is important to note that in all cases which I have encountered the ethereal solution of the fats had a pale yellow colour. This slight colour was left after the first separation of the ethereal solution of the fats from the aqueous solution of the colouring matters in dilute alkali.It was not removed or lessened by any subsequent treatment with potash solution, however oft repeated. This residual pale yellow colour is due to the fats and oils themselves, and it is not due to any added colouring matters. This remark is true of butter, imitation butter, and 6‘ oleo oil.” It is the slight yellow d o u r natural to the fat itself. It may be entirely removed without the use of chemical agents, and without any change whatsoever in the fat itself, except the abstraction of that very minute portion which carries with it the yellow colour. BUTTER COLOURS. Three mmples of butter colour were similarly treated, using, of course, smaller quantities of the samples. About 5 grams. were dissolved in 20-25 c.cm. petroleum ether, and 10 c.cm.of a 4 per cent. solution of potash were used for separation. The aqueous solution in alkali was then just acidified with dilute hydrochloric acid, and the colouring matter filtered and washed on a tared filter. It was then left behind in a resinous condition.THE ANALYST. 151 REACTIONS OF COLOURING MATTERS. Solutions and reagents were used in equal proportions, two to three Ammonia gave with Turmeric Reddish-Brown, return- drops of each. ing to original colour on driving o f NH,. Concentrated H,SO, Concentrated HNO, Concentrated HC1 No change, or only slight Dirty Yellow and Brown. Colouring Matter. Blue, becoming colourless on standing. Indigo Blue, changing to Violet. Annatto. Same. Blue, through Green and Bleached. No change, or mly dig ht Dirty Yellow. Blue, becoming Green, and slow\ changing to Violet.Annatto + decolouriaed butter. Decolourieed. Violet.. Same. ~~ Violet, changing to original colour 3n evaporation of HCI. Turmeric. Pure Violet. Violet. Turmeric + decolourised butter. Violet to Reddish. Violet. Violet to Purple Very fine Violet,. Violet to Cobal Blue, changing ti Reddish- brown. Light Blue, changing to light Reddish- Brown. Yellow, changing to Dirty Yellow. Saffron. Same. Blue, quickly changing to Purple. Dark Blue, changing quickl? to Reddish- brown. Umber Brown. Saffron + decolourised butter. Yellow becoming Dirty Yellow. Blue, through Ireen to Brown. Do. with NO, umes and odoui if burnt sugar. Carrot. Decolourised. No change. Slightly Brown. Reddish-brown ti Purple, similar tc Turmeric. Carrot + decolourised butter. Yellow and decolourised. Same. Dark Olive- Green, per- manent. Blue, changing nstantly to Dirty Yell0 w- Green. Partially decolourised. Yellow. Yellow, Reddish precipate. Magenta at margin. --_______ keen t o Yellow- ish-Green. Marigold. Green. Safflower. Decolourised. No change. Light Brown, Yellow. Yellow . Yellow. Aniline Yellow. Yellow precipate, ireated with NH, and ignited, deflagrates. Martious Yellow Pale Yellow. Yellow. Same colour :eturns on neu- tralising with NH,. Victoria Yellow. Partially decolourisod. Same. Same. All were solution; in Alcohol,

ISSN:0003-2654    

DOI:10.1039/AN8871200150

出版商:RSC    

年代:1887

数据来源: RSC

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152 THE ANALYST. NITRATES AND NITRITES (11). BY A. PERCY SMITH, F.T.C., RUGBY. IN my previous paper on this subject (ANALYST, March, 1887) I showed only that a fair agreement existed between the total nitrogen and the conjoined estimations of nitrates and nitrites. My present aim is to prove that the method gives absolutely accurate results. In my early experiments, the results were far from uniform, owing to the extra- ordinary delicacy of the napthylamine test. The source of error lay in the water used- It was necessary to prepare water absolutely free from nitrogen. To do this it is best to treat it with a copper-zinc couple for at least a week, render alkaline, and distil slowly, rejecting that portion containing ammonia. Ordinary distilled water gives a strong colouration with the napthylamine.I believe the nitrous acid is chiefly the result of oxidation of the ammonia, which all distilled water contains. After eliminating all sources of error, I found that the determination of nitrates and nitrites when known quantities were added to pure water agreed absolutely with the colours produced for comparison by known quantities of the salts used separately. For instance : A litre of nitrogen-free water has added to it 5.0 mg. N in the form of KNO,,and*3 mg.Nas KNO,. 100 C.C. is evaporated to dryness for nitrates, and the colour produced by the phenolsulphonic acid test is identical with that yielded by -5 mg. N similarly treated, Hence 1 litre = 5.0 mg. Again, 100 C.C. are tested for nitrites, and the colour is copied by *03 mg.N=.3 mg. per litre. In applying the napthylamine test, it is necessary that the solution of napthy- lamine hydrochlorate should be colourless, or nearly so. The colouration developed by standing is easily removed by animal charcoal. It is a good plan to keep charcoal in the solution, the supernatant liquid can be taken up by a small pipette, from which the drop or drops is added to the water under examination. This is especk 'v necessary in determining nitrates. Different shades (not depths) of colour may be pro d u d if attention is not paid to this point. I find the most trustworthy method is to evaporate just to dryness, or just short of dryness, add ten drops phenolsulphonic acid from a small (1 c.c.) pipette, agitate, add 1 C.C. water, and three drops strong sulphuric acid, then dilute, add ammonia in excess, and make up to 100 C.C.The napthylamine test is far superior to metaphenylene diamine for ascertaining when all nitrites are reduced by the copper-zinc couple, and its use has led me to the opinion that the surface of zinc recommended by the water committee, viz., 3 x 2 inches, is insufficient for the purpose; that is, if one desires the reduction to be completed in Similar quantities of the reagents must be used in each tube. twenty-hours. Using the following :- In 24 hours $9 3 9, 4 99 It was then kept that amount of zinc in 100 C.C. of water of 42' of hardness led to N per litrc. Naph. test. .. .. .. .. . . 1-03 Red .. .. .. .. . . 2.04 9, .. .. .. .. . . 1.71 9 , at 8OoF. for a whole day.THE ANALYST.153 In 7 days.. .. .. .. .. , . 3-71 None (1) 50 C.C. of standard potassic nitrate solution was made up to 500 C.C. with this same hard water; the total nitrogen expressed as ammonia being 10.1412 milligrammes. (2) 50 C.C. of pofassic nitrate solution was diluted in a similar manner with pure distilled water. Total N as NH,= 7.8787 mg. 100 of each was treated with 3 ' I x 2 ' I copper-zinc couple. Again. Soft Water. Hard Water. Milligrammes of NH, . . .. . . 7.8787 10.1412 In 2 days .. .. . . .. 1.3 2.5 $9 4 9 , .. .. .. .. 4.0 4-25 $9 6 9, .. .. .. .. 7.5 10.1 It would seem from this as if the hardness of the water has little or no effect upon the time required; indeed a hard water seems to be reduced the easier of the two, but the quantity of zinc exposed is no doubt the chief factor in the duration of time, as may be seen from the following experiments :- Water containing- Total solids 1040-0 ) "0;; 1 Total Am by CuZn 12.5 milligrammes per litre.Free Am Alb. ,, N 10.23 Three lots of 70 C.C. were treated with CuZn couples, having the respective surfaces of (a) 4 sq. in., (b) 22 sq. in., (c) 12 sq. in. (a) ( 6 ) (c) I n 24 hours (5 c.c.) .. *032 . . ~0272 . . *020 9 , 48 9 , .. .. *0625 .. 00625 .. *035 9 , 72 1, .. .. .. - .. *045 - -0635 x 200 = 12.5, the total amount present. Here we see in a very hard water complete reduction took place in two days with only 24 aq. in. of zinc. From these and other results, I concluded it was better to err by using too much zinc than too little, and that eight sq. in. should be invariably employed. By so doing the time required for reduction is seldom prolonged beyond the twenty-four hours. Of course I am speaking of my own experience only. It may happen that others may obtain different results. The waters in my district are generally hard, some very much so, due to the proximity of the lias. They are also highly charged with chlorine f r o m d t deposits in the soil. (We have an artesian well just beyond the town, which is of no use to anybody on account of the salinity of the water.) This may probably tend towards rapidity, whereas, according to Mr. Williams' original paper on this sub- ject (ANALYST, Vol. VI., p. 36), the presence of salts with an alkaline re-action is found to retard the speed of the reduction. The sample having 4 sq. in. was probably hished earlier.

ISSN:0003-2654    

DOI:10.1039/AN8871200152

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

154 THE ANALYST. SCHEME FOR QUALITATIVE BLOWPIPE ANALYSTS." IN the following scheme the tests are grouped in an order favourable to rapid work, and the attempt has been to give an amount of detail that will suffice for most analyses. Substances of unusual complexity will need special treatment that the scheme does not pretend to outline, and at all times successful work will be probable only when the analyst has previously acquired a fair knowledge of the reaction of the simple oxides. The substance may contain :-Al, NH,, Sb, As, Ba, Bi, Bo, Br, Cd, Ca, C1, Cr, Co, Cu, F, Au, I, Fe, Pb, Li, Mg, Mn, Hg, Mo, Ni, P, K, Se, Si, Ag, Na, $r, 8, Te, Sn, Ti, W, U, V, Zn. TESTS UPON TIIE UNROASTED SUBSTANCE. BY A. J. MOSES. 1. In narrow glccsa tu6e closed at one end. Heat in the flame of an alcohol lamp, at first gently, and then to redness.Note all changes. Moisture in the upper part of tube . . .. .. H20 Odourless gas that assists combustion . . .. .. 0 Pungent gas that whitens lime water . . .. . . CO, Odour of prussic acid . . .. .. .. . . CN ,, of putrid eggs . . .. .. . . . . H,S ,, that suffocates, fumes colourless .. . . so, 9 9 $ 9 ,, violet . . .. .. I 9 , 9 , ,, brown . . * . . . Br 9 , 9 , ,, greenish . . . . . . c1 9 , 99 ,, etch the glass . . . . F1 ,, of nitrous acid, fumes reddish-brown . . . . N,OB ,, of ammonia, fumes colourless or whito . . .. NH, Sublimate white, fusing yellow . . .. .. . . PbCI, 9 , ,, yellow hot, infusible . . .. . . HgCl 9 , ,, and volatile . . .. . . . . NH, (salts) 9 9 ¶, ,, fusible . . . . . fZgC1, 7 9 , j fusible, needle crystals ... . Sb,O, 9 , ,, volatile, octahedral crystals . . . . As,O, 1, ,, fusible, amorphous powder . . . . Too, Y 9 ,, does not collect in globules . . As, Cd, Ts ,, red when hot, yellow cold . , .. .. s ,, mirror-like, collects in globules , . . . Hg ,, dark red when hot, reddish-yellow cold . . As& ,, black, when hot, reddish-brown cold . . Sb,S, ,, black, but becomes red when rubbed .. HgS ,, red to black, but becomes red when rubbed . . from white to yellow, cools yellow . . .. PbO Se Colour of substances changes 9 , ,, yellow, cools white . . .. ZnO 9 , ,, dark yellow, cools light yellow Bi20, 9 , ,, brown, cools yellow . . . . SnO, 9 , ,, brown, cools brown . . .. CdO ,, yellow or red to darker, cools green * . Cr,O, ,, red to black, cools red .. .. . . Fe,O, ,, blue or green to black, cools black . . CuO * School of Mines Quarterly.THE ANALYST. 155 2. In narrow glms tube open at both ends. Place the assay near the lower end of the tube, and heat gentIy, and then strongly increasing the air current by holding the tube more and more nearly vertical. Odour that suffocates . . .. .. .. ,, of rotten horseradish . . .. .. ,, of garlic .. .. .. .. 99 ,, non-volatile powder . . 9, ,, non-volatile fusible powder 9 , ,, non-volatile fusible powder ,, grey red at distance . . .. ,, metaallic mirror . . .. .. Sublimate white volatile octahedral crystals ,, yellow hot, white cold, blue in R. F. ,, brown hot, yellow cold, fusible . . 3. Alone on clmcoal. Heat with gentle 0. F. Sb.-Volatile white coat that disappears in R.F. tinging the flame green. As.-Garlic odour and a faint white coat that disappears in R. F., tinging the flame azure blue. Se.-Horseradish odour, and a steel grey coat that disappears in R. F., tinging tho flame azure blue. Te.-White coat with red or yellow border that disappears in R. F., tinging the flame green. Change to gentle R. F. Cd.-Brown coat surrounded by peacock tarnish. The coat heated in a closed tubs with Na,S,O, gives a bright yellow mass. Heat strongly in both flames, and if the presence of Te is suspected place a bit of porcelain so that the fumes pass between it and the ccal (or test a separate portion on a-plaster tablet). As, Sb, and Cd may give stronger tests. Zn.-White not easily volatile coat, bright green with cobalt solution. Sn.-White non-volatile coat close to assay, blue green with cobalt solution. Te.-Moisten the film, which forms on the porcelain, with concentrated H2S04, and Dissolve any coat that forms in Ph.S., and treat on coal with R. F. and tin. Sb or Bi.-A dark grey to black bead. White coats may form from Mo Pb Bi or alkalis, yellow coats from Pb or Bi, brown or red coats from Cu or Mo, and the ash of the coal may be white or red. I f these coats interfere with the Sb test, the Pb and Bi may be held back by adding a little boracic acid. heat gently; the acid will be coloured a fine red. 4. With soda on coal. Make a paste with the substance, soda, water, and charcoal dust, and heat strongly with R. F. As and Cd should be noticed here even in small amounts.156 THE ANALYST. If any coat forms, moisten it with cobalt solution, and blow a strong blue flame Zn.-Bright green.Sn,-Blue green. Dig up the coal containing the soda, and place it upon a silver coin, moisten, crush, S, Se, or Te.-The c i n will be blackened. If the soda effervesces during fusion, look for SiO, or TiO,. on t7g substance. and heat. Examine it also for metallic particles, and note whether they are e.g., malleable, magnetic, brittle, red, etc. 5. Vitlt, bismuthflm. Treat the substance on coal to remove the excess of Sb, As, and Hg, by gcntle Mix with an equal volume of the 0. F., and excess of Cd by gentle R. F. flux, and heat gently upon a plaster tablet. Pb.-Yellow coat of iodide a t distance, yellow oxide nearer. Bi.-Red coat of iodide at distance, yellow oxide nearer. Bi and Pb.-Orange coat of iodide at distance.Make a similar test on coal, first moistening the coal near the assay with cobalt Blow a strong flame upon the substance. Sn.-A bluish-green coat (which is not injured by the P b and Bi coats). White coats may form of K I or K,SO,, and at times the red iodide of Bi is fringed 6. Im mutrass with soda. Mix the substance thoroughly with soda, and heat. Hg.-Metallic mirror that can be collected into globules. Cd, Te, and As.-Metallic mirrors that cannot be collected into globules. NH,.-Odour of ammonia. 7. In, matrass with KEIISO,. Mix the substance with KHSO,, and heat gently. Br.-Brown fumes. 1.-Violet ,, ,, emerald-green 9, 9 , C1.-Greenish ,, ,, azure-blue $9 9 , N20,.-Brown fumes, recognisable by odour.Fl.-The glass of matrass will be etched. solution. with the yellow of Bi. Break matraw, and heat mirror for odour of AF,~,. Gives greenish blue flame in Ph. S. bead with CuO. I f a moistened strip of Brazil wood paper be inserted at one end of an open tube, and at the other a mixture of powdered phosphorus glass and substance be fused, the paper will be made straw colour, and the glass etched, and made dull and cloudy throughout, or in patches. 8. With dilute acid. Heat substance gently with dilute HNO, or HCI. CO,~-Effervescence continuing after flame is removed (H,S and C1 are sometimes evolved with HCl, but may be recognised by their odours.THE ANALYST. 157 TESTS UPON THE ROASTED SUBSTANCE. If the substance has been proved to contain no As, Sb, or S, proceed with No.9, but if not, submit the substance to a slow heating in the 0. F. to drive off S, As, Sb, etc., and thus leave the metals mainly as oxides. Turn the material occasionally, and if it agglomerates, repulverise, and again roast. Continue till no noticeable fumes are given off. 9. I n phosphorus salt b e d . Note all the changes with small and larger amounts of the substance dissolved, and The changes and their simpler confirmations are as follows :- with treatment in both 0. F. and R. F. Mn. Cr. Ur. Mo. V. Co + Fo co. W. Ti. Ni. Fe. Fo + Ur. Fs + W. Fe +Ti. cu. In R. F. Cold. Colourless Green ,9 99 ,, Dull Green Blue Violet Yellow Brown or Bed 9 9 In 0. F. Hot, Brown Reddish Yellow Greenish Dark Yeliow Green Blue Yellow Brown Dark Yellow Red to Yellow $ 9 99 ,, Opaque Red or Green Green In 0.F. Confirmation Cold. Soda bead 0. F. Violet Bluish-Green Green Yellow 99 Brown Colourless White Light Yellow 97 Green 9 , Blue On coal with Sn Colourless Green 9 , Violet Yellow Colourless Light Yellow Green to Colourless Greenish Green Light Yellow Blue to Wine Colour 9, Violet Blue Opaque Red SiO,.-The hot bead cannot be made perfectly clear, but is semi-transparent. Touch hot bead with NaNO,. Mn.-Violet colour. I f Cu or Co obscure the tests treat as in No. 11. The absence of Mn and Ni is not proved until special tests have been made. The SiO, test is best made upon a small fragment of the substance. The bases of most silicates dissolve, leaving a translucent mass or “skeleton ” of the general shape of the fragment, and visible in both the hot and cold beads.10. Reduction colour tests. Saturate two Ph. 5. beads with the substance in 0. F., treat one of them on coal with Sn, and strong R. F., pulverise and dissolve separately in cold dilute (1-4) HCl with the addition of EL little Sn. Let the solutions stand for some time, and then heat them to boiling. The Oxidised Bead Yields The Reduced Bead Yields In Cold Solution. In Hot Solntion. I n Cold Solution. I n Hot Solution. W. Blue Deep Blue Deep Blue Deep Blue Mo. Green to Blue Wine Brown Brown Faint Brown with Black precipitate Ti. Faint Violet Violet and turbid Violet and turbid Violet V. Bluish Green Green Green Green Cr. Green 9 , 9 9 9 9 Ur. $9 9, 9, 9 9158 THE ANALYST. 11. Separation of Hi, Co, and Cu.If the absence of Ni not proved, or Co obscures the tests, dissolve the substance in borax on coal to saturation, and treat for five minutes in hot R. F., by which the Cu, Ni, and some of the Co will be reduced. If much Pb or Bi is present, the reduced button will be large enough to handle, but if not, add either a small (50 111.5.) gold button with a little lead, or, if much Cu is present, add only lead. Separate the button and the slag (saving both) and scorify the button with BO, t o remove the lead, and then with frequently changed Ph. S. The metals which have united with the gold or lead will be successively oxidised, and their oxides will colour the Ph. S. in the following order:- Co.-Blue, hot; blue, cold. Ni.-Brown, hot; yellow, cold.Cu.-Green, hot ; blue, cold. The slag should contain the more easily oxidisable metals, and be free from Cu, Ni, If Pulverise the May stay in the slag. May give green with Co or Cu. Made opaque red by Sn and R. F. and Ag. present it must be removed by further reduction with Ph. slags, and dissolve a portion in Ph. S., and treat as in No. 9. Test a portion with Ph. S. and Sn to prove absence of Cu. 12. Fusion for silver. Fuse with test lead and borax glass. Continue the blast about five minutes, using R. F. Separate slag and button, and scorify the button with fresh borax. Transfer the butt.on to a cupel, and blow a gentle oxidising flame across it. I f the litharge is dark or the button freezes while still large, scorify again with borax, and add more lead until there remains only- Ag.-A bright, spherical button, not altered by further blowing.(If tho button is flat, add test lead and again cupel.) Au.-A residue after boiling the Ag in HNO,. 13. Substance with cobalt solution. Heat the substance strongly on coal; cool, and moisten with cobalt solution. Al. Pink, reheated, is blue. Mg. Pink to blue, reheated, is pink. Ba* $9 ,, brown. Ca. Blue to green, ,, grey. SiO,. ), ,$ faint blue. Sr. Blue to brown, ,, grey* Violet may be MgzP20,. 14. Plame tests. Moisten a clean platinum wire with HCl, dip it in the substance and heat in the Note the colour of the flame There may also be blues from fusible compounds, and greens from no2, ZnO, SnO,. blue flame, both at the tip and near the wick. with the naked eye and through a cobalt blue glass.Alone. Through blue glass. Na. Yellow. Invisible. Ba, Mo, and B. Yellow-green. Bluish-green. Ca. Yellow-red. Greenish-gre y . Sr and Li. Crimson. Violet. K. Violet. Purple-red. Cu, As, Pb, Se. Blue. Blue.THE ANALYST. 159 Make similar t a t with H,SO,. Boa-Yellowgeen. P.-Instantaneous blue-green, that may be overpowered by the green of Bo. The improved tests will be- I n such a case place a piece of Mg wire in a closed tubo, and cover the wire with a mixture of soda and the substance. Heat till the mass fuses ; cool, and add water. P.-Evolution of phosphoretted hydrogen. Make a paste of boracic acid flux and substance, and treat at tip of the blue flame. Boa-Yellow-green. Li.--.Pink to carmine. Dissolve substance in Ph. 5. to excess ; add NaCI, and heat in flame gently. C'u.-Azure blue flame. Pb,-Azure blue flame a t very high heat. Just after the water is driven off there may be- NONTHLY RECORD OF ANALYTICAL RESEARCHES INTO FOOD. TESTINQ FOR BORON IN MILK, AND SIHILAR FLUIDS. M. KRETZSCHMAR. Chem. Zeit. XI. (No. 32), p. 476.-The author overcomes the difficulties in detecting the presence of boron in milk by means of the flame react,ion, by employing the following method of procedure which is capable of rapid execution. The milk is well-shaken up (m any calcium borate present, is liable to settle) ; 5 to 6 C.C. are then transferred to a flat dish, and evaporated down to about $ of the original volume. 5 to 6 drops of fuming hydrochloric acid are then added, and the evaporation continued, whilst a non-luminous flame of a Bunsen burner is directed across the dish. If any appreciable quantity of boron is present the flame will be tinged with green ; in fact, the volatilization is so complete that the green colour has frequently disappeared before the other volatile con- stituents of the milk begin to affect the flame. It is of course impossible to tell by this means whether the boron is present as boric acid or a borate. F. W. T. K.

ISSN:0003-2654    

DOI:10.1039/AN8871200154

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

THE ANALYST. 159 MONTHLY RECORD OF ANALYTICAL RESEARCHES INTO DRUGS. THE ASSAY OF OPIUM. BY E. DIETRICH. Der Pharmaceut.-The author says that he is convinced that reliable methods are known to manufacturers, but are kept secret because they constitute parts of manufacturing processes. He has tested Fliickiger’s method under many various conditions, to detect its defects. These were found to be : The addition of alcohol. Geissler has already demonstrated that it prevents the formation of morphine and aids separation of lime salts. The duration and intensity of shaking exerts an influence on morphine separation. When ammonia is added to mor- phine solution a flocculent precipitate precedes the crystalline precipitate. Examination showed the former fo be narcotine. It was found when opium solution isneutralized by ammonia, narcotine only is precipitated j this can be filtered off, and when more ammonia is added, morphine separates. These facts induced Dietrich to work out a method for160 TEE ANALYST. which he claims the following advantages : Time of emmination is shortened ; simplicity of manipulation ; no shaking ; separation of constituents ; constant results, and complete extraction of morphine.These points are illustrated by a large array of figures given in a table. For practical use, directions are given under three heads, viz. : 1. For Opium.-6 grms. air-dry opium is macerated-shaking at intervals-with 60 grms. distilled water, for twelve hours, and filtered; to 50 grms. of the filtrate 2 cubic centimetres normal ammonia is added and filtered through a star filter of 10 cen- timetres diameter; 44.2 grms.of /the filtrate (=4 grms. of opium) is mixed with 10 grms. ether, in an accurately weighed Erlenmeyer wide-mouthed flask, rotated for one minute until the solution is well saturated with ether; 4 cubic centimetres normal ammonia is now added, rotated until mixed, and placed aside for six hours at an ordinary temperature. The ethereal layer is separated and filtered through a filter of 8 centimetres diameter ; 10 grms. ether is again mixed with the opium solution in the ffask, rotated for a few moments, and the ethereal layer filtered. The aqueous solution is then filtered without detaching crystals from walls of flask, and the flask and crystals are twice successively washed, each time with 5 cubic centimetres of water which has been saturated with ether.Flaskand filter are dried at looo C. Contents of filter are put into ffask by The morphine in well-developed crystals can be removed from paper without loss. Z.-Examination of Opium Extract.-3 grms. of extract is dissolved in 42 grmsa water, placed aside one hour, 2 cubic centimetres of normal ammonia added and filtered rapidly through a filter of 8 centimetres diameter ; 31.7 grms. filtrate (= 2 grms. ex- tract) is then treated as given under previous heading. 3. Examination of Tirtcture Opium.--SO grms. tincture of opium is evaporated one-half, and sufficient distilled water added to restore the original weight; 2 cubic centimetres normal ammonia is added and filtered as above. 41.6 ,arms. ( = 40 grms. tinctlire of opium) of the filtrate is treated as given under heading No, 1. of a hair pencil, and dried until the weight remains constant. W. H. D. TEST FOR SULPFICRED Hops.-C.B. Gaz., Vol. XI., p. iii. If steam is conducted through hops they give up their hop oil when it condenses. I f such oil be obtained from sulphured hops, when phosphoric or any other acid is added, a strong odour of sulphuretted hydrogen is developed, the presence of which can be promptly ascertained by means of lead salt. This simple test enables us to distinguish sulphured from un- sulphured hops with certainty, the oil from unsulphured hops showing no such reaction. W. H. D.

ISSN:0003-2654    

DOI:10.1039/AN8871200159

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

160 THE ANALYST. MONTHLY RECORD OF GENERAL RESEARCHES IN ANALYTICAL CHEMISTRY. BY R. R. TATLOCK, F.R.S.E. ESTIMATION OF MINUTE PROPORTIONS OF IRON IN THE PRESENCE OF ALUM OR SULPHATE OF ALUMINIUM. Condensed from the author’s original Memoir, presented to the Glasgom Section of the S.C.1.-There are two methods commonly in use for the detection and estimation of very small proportions of iron, One of these is based upon the depth of blue or green colour produced byTHE ANALYST. 161 -~ ~ addition of potassium ferrocyanide, and the other upon the intensity of the red d o u r obtained by addition of solution of an alkaline thiocyanate to acidified solution of the substance under examination. The application of ferrocyanide for the determination of iron is not at all desirable, for various reasons.The tint is very variable-between a bright green and a full blue, even for the same proportion of iron, even when the other conditions are as nearly as possible equal, and comparison of intensity is thereby rendered unreliable; there is often a difiiculty in keeping the prussian blue formed in perfect solution, even when oxalic acid is added ; the composition of the blue produced cannot always be relied upon as uniform; and, lastly, it is not desirable to employ a reagent of which iron forms an essential constituent. On these grounds the use of this reagent for quantitative purposes is not to be recommended. The employment of thio- cyanate of potassium (KSCN), or of ammonium (NH4SCN), for the determination of small quantities of iron, particularly in commercial aluminium salts, is, of course, common to all laboratories. It has been practised for many years, both for scientXc and technical purposes, and, as is well known, depends on the formation of the red ferric thiocyanate (Fe,GSCN), soluble in water, alcohol, and ether.It is often recklessly referred to aa (‘the sulphocyanide process,” without reference to the marked effect upon the results of alteratiom in the working conditions, such as amount of reagent used, proportion of free mid present, presence of oxidisers employed to convert ferrous into ferric iron, etc. In his process the author takes advantage of the solubility of the red colour in ether on the following grounds :- Ether extraction of the red ferric thiocyanate has the following advantages, under all working conditions : It develops the red tint to triple intensity, besides increasing its brilliancy.It obviates the difljiculty too commonly met with, of comparing colours in solutions which are opalescent from mechanical impurities, and in solutions which have naturally a brown or yellow tinge. It admits of the concentration of the iron, by the extraction of a large volume of ferric solution with a small volume of ether, and in this respect it is to micro-iron-determination what distillation is to Nesslerising. Finally, it does away with the injurious effect which aluminium salts have of preventing the develop- ment of the red colour, and thus admits of iron being estimated in alum with precision, by comparison with standard ferric solution in water, without the necessity of employing an absolutely iron-free alum for comparison.On these considerations the author has worked out (and illustrated by a large number of test analyses) the following process, which for simplicity, certainty, and rapidity is unsurpassed, if equalled, by anything in quantitative analysis; while for accuracy it is enough to say that it is capable of estimating iron in alum with the greatest ease to a unit of the fourth place of decimals (= *0001) per cent., or one part per million, and, with a little more trouble, to a tenth or even a hundredth of t h t amount‘ 1. Make a standard solution of iron-alum (Fe23s04, K,S04 + 24H20) by hiving 8.606 grms. and making up with distilled water to one litre. As the alum contained 11*62 per cent of Fe, thb will give a solutiob containing exactly 1 grm, of metal per 1000 cc.This solution should contain no free acid, and it will keep clear for weeks, Weaker standards become turbid, hence they must be made from this when required.162 THE ANALYEIT. 2. Place 1 grm. of the finely-powdered sample in an ordinary stoppered sample-tube of about 30 cc. capacity, and having three file marks-at T i , 10, and 20 cc. respectively. Add 1 cc. of normal iron-free sulphuric acid, and make up to the lowest mark with pure water. Dissolve the alum by shaking the tube for a few seconds in a beaker of hot water, and when dissolved cool the solution again by holding the tube in cold water for a few seconds more. Add now 0.2 grm. of iron-free ammonium thiocyanate, and make up to 10 cc.with pure water. 3. Place 1 cc. of the standard iron solution of 1 in 100 cc. flask, and make up to the latter volume with distilled water. Now place 1 cc. of this reduced iron standard in a similar stoppered sample tube to that of 2, add 1 cc. of the normal acid, make up to the lowest mark with water, add 0.2 grm. of the thiocyanate, and make up to the 10 cc. with water. 4. Finally, fill up both tubes to the 20 cc. mark with ether and agitate them thoroughly. As soon as the contents settle compare the tints, and, if unequal, of course one or more further trials are made with greater or less quantities of standard iron- solutions as may be necessary. Water takes up about &th of its volume of ether, and it so happens that this retained ether holds its proportion of the ferric thiocyanate; but as this is equally the case with the sample and with the standard, it is of little consequence ; but in all delicate experiments the ether solution should be drawn off into graduated cylinders after adding a washing with an equal volume of ether, and compared there in any way most convenient. Precat&om.-?’he necessity for iron-free reagents has already been referred to, The thiocyanste may be prepared pure enough for all ordinary purposes by twice re- crystallising the best obtainable in a very feebly acid solution, and washing with ether till the washings are colourless.Although the product is not absolutely iron-free, it appears so under working conditions. The acid may be obtained pure enough by distilling into water a t a temperature much below its boiling point, of the purest obtainable oil of vitriol, Of course in all cases the reagents will be tested collectively by a blank experi- ment.The same precautions must be observed with regard to the vessels employed; all must be thoroughly digested with strong hydrochloric acid, and thoroughly washed before use; they should be kept under a glass shade, and employed for nothing else. The operations should be conducted with as little light as pomible, and certainly never in direct sunlight or even in strong diffused daylight. Oxidisers should be avoided, particularly peroxide of hydrogen, which, even in small quantity, destroys the red colour. Of course they would be required for ferrous iron, even small amounts, if the ether extraction were not adopted, but not otherwise, as when the ether is employed the iron is completely oxidised to the ferric state, probably by the ozonisation of the air with which the fluid is agitated. So completely is this the case that it is of no moment whether the standard iron solution be made from a ferrous or a ferric salt, provided it contains the same proportion of metal,

ISSN:0003-2654    

DOI:10.1039/AN8871200160

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

162 THE ANALYEIT. NOTICE TO OUR READERS. Ewatwm-In Prdessor v. Asb6th’s paper on the ‘‘ astimation of Starch ” in last month’s ANALY~T, on the last line of page 139, the equivalent of starch to baryta is printed as 432, while it should evidently be 4.23, or more strictly 4.2353, because C, H, 0 fL BaO would require f+# = 4.236%

ISSN:0003-2654    

DOI:10.1039/AN8871200162

出版商:RSC    

年代:1887

数据来源: RSC