SCIENTIFIC AND ANALYTICAL CHEMISTRY.

On the Detection of Alum in Bread,

by WILLIAM CROOKES.

THIS problem is one of far more difficulty than is generally imagined, and it is, doubtless, to this fact that the discordant results obtained by different analysts are to be attributed one stating that out of sixty-four samples of bread purchased at various shops in poor neighbourhoods at the East of London, where, if anywhere, adulteration would be practised in the most barefaced manner, not a single one was found to contain alum: whilst another analyst, with equal positiveness, mentions the name of a baker who is, in his opinion, almost the only person in a large district at the West End of London who sells unadulterated bread, and proceeds to state that more than 87 per cent. of the bread in London is adulterated. Very few of those who have published anything on this subject give details respecting the process they adopt, but in most instances it seems to be somewhat to the following effect:-The bread is first charred and burnt nearly to an ash; the latter is then boiled in diluted hydrochloric acid, with which a little nitric acid has been mixed; ammonia is then added, and the precipitate which it produces is boiled in potassa. After filtration, hydrochloric acid is to be added in excess, and then ammonia, when it is supposed that the precipitate will consist of alumina. With a pure solution of alumina to start with, doubtless this process would give accurate results; but it must be remembered that in bread the alumina would be accompanied by phosphoric acid, as well as phosphate of lime and phosphate of magnesia, each of which would make its appearance in the last precipitate with ammonia, and would, consequently, pass for alumina. But, granting that this tendency of the phosphates of lime and magnesia to simulate the reactions of alumina had been provided against, it seems to have been almost entirely overlooked by popular writers on this subject that whenever alumina and phosphoric acid meet together in solution, they adhere with the greatest pertinacity, and will infallibly appear together in the last precipitation. I should not have deemed these points worthy of mention did I not know that many analysts are habitually employing similar processes to the above, and are even estimating quantitatively the amount of adulteration in bread by weighing this precipitate of the mixed phosphates of lime, magnesia, and alumina, and calculating it as pure alumina.

My attention was first drawn to this subject by the fact that a sample of bread which was known to be entirely free from adulteration had been pronounced by a somewhat experienced analyst as being largely adulterated with alum. My assistance was asked in order

to disprove this injurious allegation, and, having accordingly submitted the subject to a somewhat lengthened examination, I am induced to lay the results before the readers of the CHEMICAL NEWs, in the hope that when the attention of chemists is drawn to the subject, it may be investigated as fully as its commercial importance deserves.

The great difficulty in my hands has been to devise a process which should not confound other things with alumina. It was easy to frame various modes of operating by which a minute trace of alumina could be detected, but I was for a long time baffled by finding that they were equally delicate in their reactions, whether alumina were present or not. In fact, I do not hesitate to say that the accurate analysis of a mixture of those phosphates which are precipitated from an acid solution by ammonia is one of the most difficult problems in inorganic chemistry that the chemist is liable to meet with in technical analysis. I do not pretend to have yet solved the difficulty, but the process which I have at last adopted has at least the merit of not showing the presence of alumina when that body is absent. It has, on the other hand, the inconvenience of being rather tedious in its manipulation, and to some may seem to be needlessly complicated. No one can be sensible of this fact more than myself; but of the numerous methods which I have tried, both with and without separating the phosphoric acid, this was the only one which invariably gave me trustworthy results.

The bread, of which at least 500 grains should be taken, is first to be incinerated in a platinum or porcelain dish, until all volatile organic matter has been expelled and a black carbonaceous ash remains. The temperature must not be raised much beyond the point necessary to effect this. Powder the coal thus obtained and add about thirty drops of oil of vitriol, and heat until vapours begin to rise; when sufficiently cool, add water and boil for ten minutes. Filter and evaporate the filtrate until the fumes of sulphuric acid begin to be evolved, when ten grains of metallic tin and an excess of nitric acid must be added, together with water, drop by drop, until action between the acid and metal commences. When all the tin is oxidised, add water and filter. Evaporate the filtrate until fumes of sulphuric acid are again visible, when more water must be added, and the liquid again filtered if necessary. To the clear solution now add tartaric acid, then ammonia in excess and sulphide of ammonium. Evaporate the liquid, containing the precipitate suspended in it, in a dish until all the smell of sulphide of ammonium has disappeared. Filter, evaporate to dryness, and ignite to get rid of the organic matter. Powder the black ash, boil it in moderately strong hydrochloric acid, filter, add a crystal of chlorate of potash, and boil for a minute. Now add chloride of ammonium and ammonia and boil for five minutes. If, at the end of that time, anty precipitate is observed it will be alumina. From he filtered

NEWS

In an experiment to ascertain whether all the moisture was removed by drying in vacuo over SO, a quantity of 210° to 212° for nine hours in the exsiccator lost a little about two grammes by exposure to a temperature of less than one and a-half milligrammes.

Heated on platinum foil the ammonia picrate of copper explodes with some violence and with a dazzling light.

Ammonia-picrate of Cobalt.

To a solution of protochloride of cobalt prepared from chloride of purpureo-cobalt in the manner recommended by Gibbs and Genth in their interesting and valuable paper on the ammonia-cobalt bases, a large excess of ammonia was added, and to the filtrate, cold saturated solution of picrate of ammonia. An abundant highly crystalline precipitate falls at once, which after drying is yellowish green; while moist decomposes with great facility with separation of cobaltous oxide.

6293 substance gave 4784 picric acid.

Calculated.

Found.

I.

II.

Mean.

C12H2N3O14 Ag 2NH3

61.62

6173

61.11

61.42

29.19

27.96

.6075

'4594

9'93

*5416

100.00 99.62

•6075

99'30

The silver falls below, and the ammonia exceeds the calculated amount in consequence of the impossibility of obtaining the salt quite free from admixed picrate of ammonia.

This beautiful salt appears to be one of the most permanent of this very unstable class of substances. It dissolves readily in hot water containing ammonia, sparingly in cold, and crystallizes in fine needles from the hot solution. Heated on platinum foil it detonates and leaves a brilliant spot of metallic silver.

Ammonia-picrate of copper.

A cold saturated solution of picrate of ammonia added to an ammoniacal solution of sulphate or nitrate of copper, immediately throws down an abundant precipitate, which, after washing with strong solution of carbonate of ammonia, and afterward with dilute ammonia, exhibits a beautiful pale greenish yellow colour with a shade of red through it. It is in fine scales, and much resembles the dust of the wings of butterflies.

1 American Journal of Science and Art.

1641 protosulphate of cobalt.

2065 chlorhydrate of ammonia.

Which results lead to the formula :

2NH,COO.C12 H2

0+ HO.

and undergoes a commencement of decomposition in This salt is much more unstable than the foregoing, washing. Even when this part of the operation is performed with great care, using carbonate of ammonia ammonia is washed through, and as cobaltous oxide is and dilute liquid ammonia, a portion of picrate of not easily soluble in ammoniacal solutions, it is not easily removed by washing with such. It is also probable that more or less cobaltous oxide is thrown down with the precipitate, as the latter at the first moment crystalline becomes quickly more and more

curdy; and ammoniacal solution of cobalt by mere dilution with water throws down a bright green precipitate. In the preparation of the ammoniacal solution, it is better to drop a strong solution of cobaltous chloride into a large excess of ammonia.

Like the foregoing, this salt explodes by heat.

Ammonia-picrate of Zinc.

To a solution of pure sulphate of zinc, chlorhydric acid was added in sufficient quantity to prevent precipitation by the subsequent addition of ammonia in excess. To the clear solution, a hot, strong solution of picrate of ammonia was added. Immediately the whole became nearly solid with beautiful yellow needles and scales; the beaker was rapidly cooled by cold water, the contents thrown on a filter, and washed first with a solution of carbonate of ammonia, mixed with caustic ammonia, and, finally, with dilute caustic ammonia alone.

The splendid gold-yellow mass of interlaced needles and scales was more or less decomposed, even by the most careful washing, so that the brightest and purest parts only could be taken for analysis, nor were even these satisfactory.

C12H2N3O14 mean of 5 determinations 81.26

NH, Zn

9'06 10.08

100'30

requires :

79.692

8.913 11.395

100.000

The fact that when a strongly acid solution of zincchloride is supersaturated with ammonia, the compounds 2NH, ZnO HCl and NH, Zn O HCl successively erystallise out, speaks in favour of the latter hypothesis. Ammonia-picrate of Cadmium.

The cadmium salt is obtained and purified in exactly the same manner as the zinc, which it nearly resembles; it is, however, not so bright in colour, but pure canaryyellow. Like the zine salt, it re-dissolves in its mother liquid by heat, without decomposition, but, like almost all the compounds here described, when washed with pure water on a filter, the picric acid and ammonia wash through. A grayish-white residue of oxide of cadmium

remains behind.

Heated on platinum foil, the salt deflagrates with a beautiful green light.

7170 substance gave 5247 picric acid.

1653 sal ammoniac.

.6622

*4877 .8452

*2945

Ammonia-picrate of Chromium.

This salt is easily obtained from an ammoniacal solution of chromoxide, which may be prepared in the following manner :

Three grammes of potash chrome alum are dissolved in water by boiling, the solution removed from the fire, and 14 cubic centimètres of pure concentrated sulphuric acid and 90 cubic centimètres of liquid ammonia added. A strongly alkaline, beautiful purple solution is thus obtained, which may be preserved in well-stopped vessels, quite filled, for a considerable time.1

To a solution prepared in this manner, a strong, hot solution of picrate of ammonia, not in excess, is to be added. Some precipitation follows at once, which increases very much as the solution cools. The precipitate is thrown on a filter and washed with dilute liquid ammonia. It consists of splendid green, metallic-looking scales, which, if heated with a considerable quantity of water, even strongly ammoniacal, are decomposed with precipitation of chromoxide. On cooling, picrate of ammonia crystallises out. Even with very careful washing, the salt is always partly decomposed, with separation of green oxide of chromium.

The portions that were least decomposed were selected, but were not sufficiently pure to give any satisfactory result, although a number of specimens were analysed. 1. 6949 substance gave 5864 picric acid. II. 5537 III. '4446 99 IV. 4446

v. '6949 These numbers correspond to 1. C12H NO.

83.06 2.78, 2.63

results which do not lead to any satisfactory conclusion, but show that the quantity of ammonia salt necessary to keep the chromoxide in solution throws down picrate of ammonia simultaneously with the ammonia-picrate of remarkable. chromium. This salt is very beautiful; its lustre is

Ammonia-picrate of Manganese.

If ammonia be added to a solution of manganous

1 While studying the chromium salt, I met with Frémy's "InvesIn it the author states that the tigation of the Sults of Chromium." salts of chromoxide, modified by boiling (green modification), are insoluble in ammonia, except after having been boiled in acid and precipitated by ammonia. It will be observed that the above process is not in conformity with the opinion of M. Frémy, as it is there shown that the green modification, produced by boiling, is rendered soluble in ammonia by the simple addition o sulphuric acid, and without any application of heat. The solution in ammonia is always complete, and the process never fails.

sulphate, previously rendered strongly acid with chlorhydric or nitric acid, a considerable quantity of manganese escapes precipitation, an extremely unstable solution is obtained, which, in a few minutes, even before filtration is ended, becomes cloudy again. To give the solution more stability, the presence of a very large quantity of ammonia salt is necessary,-a circumstance very unfavourable for the production of a pure ammonia-picrate, as, by a solution so strongly saline, picrate of ammonia (as already observed) is at once precipitated. The following were the observations made:

A. If a cold solution of picrate of ammonia be poured into an ammoniacal solution of manganese, prepared by adding to a concentrated solution of manganous sulphate an equal volume of dilute chlorhydric acid, and then ammonia in large excess, there falls a precipitate of brilliant, satiny scales, mixed, however, with precipitated manganous oxide, which is readily distinguishable on the filter.

B. If the ammoniacal solution is added to a hot, moderately-strong solution of picrate of ammonia, and the whole be rapidly filtered, the liquid passes through before complete precipitation takes place, and on cooling, granular crystals are obtained, which rapidly turn brown in the air. Heated on platinum foil, they turn brown, melt, and deflagrate sharply, with a brilliant white light. Neither A or B yield a salt sufficiently pure for analysis. A always contains admixed manganous oxide, and B picrate of ammonia. A bears considerable resemblance to the chrome salt just described.

1'0115 of B gave 9115 picric acid.

So large a per-centage of picric acid corresponding to 8972 per cent. of the molecule CH.NO, probably indicates a large admixture of picrate of ammonia, which

cannot be removed. The formula

NH,MnO. C12 NO requires 84'59 per cent.

H2 3NO,

Ammonia-picrate of Iron.

An ammonia picrate of protoxide of iron appears to exist. If solution of protosulphate of iron be mixed with one of sal ammoniac, and then with liquid ammonia, be rapidly filtered, and the filtrate be treated with picrate of ammonia, a dark-green crystalline precipitate is obtained; thrown upon a filter, a red liquid passes through, containing a portion of the picrate of ammonia reduced by the ferrous oxide. The precipitate, when heated on platinum foil, deflagrates with scintillations. Heated with solution of sal ammoniac and caustic ammonia, it does not appear to dissolve, but ferric oxide is thrown down, and picrate and picramate of ammonia remain in solution. It was found impossible to obtain this salt in a condition to admit of even an approximate determination of its constitution.

If acetate of lead be treated with ammonia in excess, and if to the clear solution be added picrate of ammonia, a curdy precipitate, at first pale yellow, gradually deep; ening to orange colour, falls. Heated on platinum foil it detonates with violence. Boiled with caustic alkali, it disengages no ammonia. The result of an analysis showed it to be Marchand's penta-basic picrate of lead, H2

4РЬО РЬО С12 300.

The above described salts containing ammonia are all highly crystalline. The lead compound just menti one is amorphous.

Other ammonia-picrates exist, which I propose to examine hereafter.

On Arsenical Paper-Hangings, by Dr. W. FRAZER, Leeturer on Medicines to the Carmichael School of Medicine.

HAVING recently been requested by some of my friends to examine paper-hangings for them, which were suspected to contain arsenical preparations, and having in every instance obtained not mere traces, but large quantities comparatively, of this substance from the paper thus tested, it occurred to me that a description of the simple means necessary to determine the fact would be interesting, and perhaps useful to many who might be desirous of having a similar question solved.

There is ample proof that the consideration of arsenical paints is at last engaging the attention of the public in a manner it has never heretofore done, and several papers have been published on the subject in the past year. The paper which was read by my friend Dr. Davy, at a recent meeting of the Royal Dublin Society, abounds in important and practical information. He detailed in it the results of his inquiries, and alluded to several striking instances in which deleterious effects have followed the use of these arsenicated papers, and also the employment of a green arsenical distemper, or water colour, applied as a paint to the walls of rooms in a public institution in this city. He further demonstrated, and I think sufficient notice has not yet been drawn to it, that these same obnoxious colours are lavishly employed in other manufactures, as wax tapers, and in the colouring of green tarlatan for ladies' dresses, to which the poison adheres so loosely that slight friction removes it; and an instance was incidentally mentioned by Dr. Barker, proving that French confectioners have not quite given up the employment of these dangerous colourings, and in which serious results might this winter have readily occurred, from children eating their attractive but deadly sweets. It is right to state, in my opinion, that every such colouring is avoided by our best Dublin houses, and that these sweets come from abroad. To these instances I might myself add the very free use of arsenical green in the painting of blinds and woodwork. I do not purpose to enter into the details of the symptoms which are now recognised as attending the continued inhalation or absorption of small quantities of arsenic. I can readily understand that some individuals are much more susceptible of their injurious influence than others; and this is what we would be led to expect from our previous knowledge of the action of other mineral substances, such as either lead or mercury. But I think that these cases which have been accumulated add another proof to the experience already acquired on the subject, of the effects of poisonous substances in small doses, and almost, I might say, proving the existence of a general law, that "minute, but far of mineral preparations can and do produce decided and from imaginary, homoeopathic, or infinitesimal quantities well-marked symptoms in the human frame." Burton, Tanquerel, and others, have well worked out the details of the pernicious influence of lead preparations when absorbed in small and repeated quantities; and it is truly wonderful how small an amount of this metal may produce serious results. In connexion with this, let me detail the following case :-I was asked to see a woman some years since, labouring under obscure and unexplained malaise; she had wandering rheumatic pains, constipation, and colicy attacks, for which she had been under medical care for upwards of a fortnight, and as yet with little or no improvement. I chanced to look at her gums, which I always do in obscure attacks of

abdominal pain, and the well-defined blue line at once told its tale of lead as the source of the attack. I had considerable difficulty in getting any history of her exposure to its action; at last it came out that she was employed as a care-taker in an empty house; that the family had been away, and that painters were working there; and, finally, that she used to sleep in the room in which the paint-pots were kept, and that for several nights some of these pots were close to her bed. She rapidly recovered by using suitable treatment.

Copper, too, is another of those metals whose insidious action upon the system, when absorbed in small quantities for a considerable period, is undoubted; and Dr. Corrigan's purple line around the gums is as distinctive and conclusive of its presence as the blue line of Burton is well known to be of lead. In a case which I saw in Dr. Corrigan's wards, there was no doubt either as to the existence of a purple copper-poison line upon the gums of the patient, or of the presence of those symptoms which copper causes; but how was the entrance of copper into the man's body to be accounted for? His trade was that of an upholsterer's workman; he had to all appearance nothing to do with copper, and still, on strict examination into his history, it was found that for some weeks he had been chiefly, if not altogether, engaged in polishing and cleaning up old brass furniture castors, the dust from which he stated, when closely questioned, had often affected his taste unpleasantly when working at them. Yet the symptoms caused by b. th copper and lead absorbed in this gradual manner are very different in character from such as attend their

(xhibition in full medical doses.

Shall I also instance mercury,-how well recognised as the result of exposure to it in continued, though minute doses, is the metallic trembling, the palsied state of a looking-glass maker, or a button gilder, and yet how distinct from salivation, griping, and other well-known symptoms of the influence of this mineral in full therapeutic doses. In fact, we are but beginning to recognise the truth of that law which I allude to, that the influence of medical agents, especially mineral substances, over the human body, differs not only in degree, but even in essential characters, according to the doses and the mode of exhibition. Palpably I would say that one special class of symptoms will be produced by exposure to the continued absorption of minute doses; and this is noticed alike, whether the substance be inhaled by a painter working in lead preparations, a person inhabiting arsenical-papered rooms, or one breathing the fumes of mercury, or from the repeated internal employment of the deleterious substance, as in drinking leaden waters. That a distinct class of symptoms will attend the use of these same substances when employed in their ordinary medical doses, a class of symptoms best known to us from their being most frequently brought before our notice; and, lastly, that a third class of symptoms are to be traced when these preparations are exhibited in excessive, or, as they are popularly termed, poisonous quantities. I do not wish to be understood as asserting that the symptoms produced by any one of these substances, arsenic, copper, or lead, have nothing in common in these three modes of exhibition, but that they present broad and well-marked distinctions, valuable to us as practical guides, and interesting as abstract truths.

But, to return to the subject of testing arsenical paperhangings, I wish to point out a very simple and satisfactory mode of examining these papers, which was first mentioned to me by Dr. Davy. The powder detached

by scraping from the surface of the paper, or any other substance which we desire to examine for arsenic, is intimately mixed with about twice its bulk of pulverised yellow prussiate of potash, which has been previously dried to deprive it of its water of crystallisation, and the mixture is placed in an ordinary reduction-tube, and steadily heated. I always wrap a small portion of moistened bibulous paper around the tube, about half way up, to aid the condensation of the arsenic at this part, which sublimes in the metallic state. I find in practice that the yellow prussiate of potash is much to be preferred to other reducing agents, and I think it will be found that it is so simple in its action, and so satisfactory in its results, that anyone with a moderate amount of care can at once determine for themselves the presence or absence of arsenic in paper-hangings. Let me say, in conclusion, that it is not necessarily a bright-green paper that alone contains arsenic, many very pale greens and greenish-white colours also yield it; and at present I would be disposed to look with more than suspicion on almost all the green tints employed by the paper-stainer. There is no reason that this should continue, and in some of the compounds of chrome I have no doubt satisfactory substitutes might be found, even if they were more expensive than the gaudy but deadly arsenical tints.Dublin Hospital Gazette.

Note on the Estimation of Uranium and Phosphoric Acid, by M. F. PISANI.

Ir phosphate of soda is poured into an acetic solution of oxide of uranium, the metal is completely precipitated in the state of phosphate, having the formula,—

2 (Ur2 O2 O) PO5.

This precipitate, although gelatinous, deposits perfectly when hot, which allows of its being easily washed.

Estimation of Uranium.-After saturating with ammonia the liquid containing the uranium, acidify with acetic acid, then add a sufficient quantity of phosphate of soda. Allow the precipitate to deposit when hot, and wash it several times by decantation with boiling water. Care must always be taken when, after two or three decantations, it happens that the precipitate does not deposit itself readily, and the supernatant liquid becomes turbid, to add a little chloride of ammonium, which favours the settling. If this precaution is omitted, some phosphate of uranium passes through the filter, and considerably retards the filtration. Whilst the precipitate is on the filter wash it with hot water, with the addition of chloride of ammonium, and dry it artificially. Then separate it as completely as possible from the filter, calcine it in a platinum crucible, taking care to incinerate the filter separately. The calcined phosphate has generally a green tint, owing to a partial reduction, but that has very little influence on the results. The weight of phosphate of uranium, multiplied by 0,8023, gives the quantity of oxide Ur2O2, 0.

Estimation of Phosphoric Acid in Combination with Alkalies, Alkaline Earths, and Magnesia.-Although the method of estimating phosphoric acid in alkaline phosphates by sulphate of magnesia yields excellent results, yet chemists well know that a long time is required for its complete precipation, and there is always a difficulty in detaching the portion adhering to the sides of the vessel. Even in this case the uranium method of estimation can be recommended. Moreover, it must be observed, that as the equivalent of phosphate of uranium is very high (it contains 80 per cent, of oxide