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ON THE PREPARATION OF UREA.

BY JOHN WILLIAMS, F.C.S.

Having had occasion to prepare rather large quantities of Urea, I found that the result constantly fell considerably short of what I considered a satisfactory one. This led me to consider if the ordinary mode of preparation could not be improved

upon.

The result of my experiments is, that cyanate of lead is better adapted for the purpose than the mixture of salt generally present in solution, when the usual process is adopted. I proceed in the following manner:—

I

prepare cyanate of lead by fusing cyanide of potassium of the best commercial quality (containing about 90 per cent. of real cyanide) at a very low red heat, in a shallow iron vessel; red lead is added in the usual manner, by small quantities at a time with constant stirring, so as to prevent the temperature rising too much during the operation. I prefer cyanide of potassium to ferrocyanide for many reasons, but mainly because the temperature can be kept down to the lowest point.

The cooled and finely-powdered product is exhausted with successive portions of cold water, the liquid filtered, and nitrate of barium added. Carbonate of barium is thus precipitated. The mother-liquid, treated with nitrate of lead, yields pure cyanate of lead; this can be washed thoroughly, and dried at a gentle heat, and preserved for use. Unlike cyanate of potassium, it is a permanent salt, and could be produced at a moderate price, if required.

To prepare urea, it is simply necessary to digest with sufficient water at a gentle heat, equivalent quantities of cyanate of lead and sulphate of ammonium, filter and evaporate. I have found the result most satisfactory.

The compound ureas may, in like manner, be produced by substituting the sulphates of the compound ammonias for the ordinary sulphate of ammonium; the experiment has been tried and found successful.-Chemist and Druggist, March, 1868.

ON LIQUOR BISMUTHI ET AMMONIE CITRATIS.
By C. H. WOOD, F.C.S.

Through the medium of the advertisement columns of the medical journals Mr. Schacht, of Clifton, has recently cast some disparagement on the Liquor bismuthi et ammonia citratis of the new British Pharmacopoeia. As this preparation is obviously intended to represent the very elegant solution of bismuth introduced into pharmacy a few years back by Mr. Schacht himself, it becomes a matter of some interest to determine the justice of Mr. Schacht's remarks upon it. Although Mr. Schacht's process has not been published, analysis has shown that the original "Liq. Bismuthi" contains an ammonio-citrate of bismuth, and several methods have been proposed for producing this com. pound. But most of these have been somewhat complicated and troublesome.

The process given in the Pharmacopoeia possesses two great advantages. It is extremely simple and easy of execution, and it furnishes a liquor of perfectly uniform and definite strength. Assuming the materials employed to be pure, it yields a solution of ammonio-citrate of bismuth containing only nitrate of ammonia in addition. We may fairly suppose that the authors of the Pharmacopoeia considered this latter salt to be a harmless constituent of the solution, or they would have taken means to exclude it.

In the advertisements I have referred to, however, it is alleged that the Pharmacopoeia preparation will contain, in addition to the nitrate of ammonia, "almost invariably arsenic and copper, and frequently antimony, etc." These, it is stated, will be derived from the impurities notoriously prevalent in metallic bismuth.

It must be admitted that the presence of these metals in varying proportions would detract from the value of the Pharmacopœia solution, and constitute an objection to the officinal process. Having prepared several samples of this liquor, operating strictly according to the instructions of the Pharmacopoeia, I thought it desirable to examine them carefully for these metallic impurities. When the liquor was prepared from metallic bismuth, pu

rified as the Pharmacopoeia directs, I failed to detect either copper, arsenic, or antimony. In no case could I find the last two metals, but in one case I obtained a trace of copper. The liquor which contained it, however, was prepared from metal imperfectly purified, for the fusion with nitre was not carried on sufficiently. It is to be observed that the Pharmacopoeia directs the commercial bismuth to be twice fused with nitre, stirring the molten mixture for a quarter of an hour each time. Copper is the most abundant impurity of bismuth, and would most readily pass into the liquor prepared from metal containing it. When ordinary commercial bismuth is employed for the preparation of the liquor in place of the purified bismuth ordered, the resulting solution does undoubtedly contain copper, and may contain traces of arsenic and antimony; although the latter is mostly deposited from the nitric acid solution as insoluble antimonic acid, together with at least part of the arsenic as arseniate of bismuth.

Judging from the experiments I have made, I think it is safe to conclude that when the Pharmacopoeia instructions are properly carried out, the process yields with the greatest facility a solution of ammonio-citrate of bismuth which is associated only with nitrate of ammonia, and is in other respects pure and trustworthy. But the substitution of commercial for purified bismuth would be an improper departure from the directions of the Pharmacopoeia, and would be likely to cause the introduction of objectionable impurities into the preparation. The purification of the metal is an important part of the process.

Although the Pharmacopoeia process is a very satisfactory one, I have found it advantageous, in manufacturing this liquor, to depart from the letter of the instructions, and to employ, in the place of metallic bismuth and nitric acid, the crystallized ternitrate of bismuth, as proposed by Mr. Tichborne some years back. This modification of the Pharmacopoeia process, while it is in some respects more ready and convenient, happens to afford greater security for the purity of the product. It has the additional advantage also of introducing a minimum and uniform quantity of nitrate of ammonia into the resulting liquor. The crystallized nitrate is readily obtained and easily kept. When bismuth is dissolved in nitric acid, the solution, after concentra

tion, deposits well formed crystals of the ternitrate. These may be drained on a funnel, and dried by exposure to the air on a porous tile, or on white filter paper. They are perfectly definite in composition, having the formula Bi (NO3)3, 5 H2O, and they undergo no change by keeping. By long exposure to the air they slightly effloresce, but that is all. If the salt be prepared from commercial bismuth, a second crystallization only is required to render it pure. The preliminary purification of the metal may, if desired, be thereby dispensed with. 995-15 grs. of this salt contain 430 grs. of bismuth, and is, therefore, the quantity to be used in lieu of the metal and nitric acid ordered by the Pharmacopoeia.

The process I follow is arranged for a gallon of liquor, and is as follows:

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The citric acid is dissolved in two pints of the water, and the crystals of nitrate added. They rapidly dissolve, and after a little time a white precipitate begins to form. As soon as the nitrate was dissolved, the ammonia diluted with an equal bulk of water is added, little by little, until the precipitate is dissolved, and the liquid is neutral. The resulting solution is, if necessary, filtered, and diluted to the volume of one gallon.

It will be observed that I employ rather more citric acid than the P. B. orders. This I find to be desirable when the crystals are employed in lieu of the nitric solution.

The quantities for a pint are as follows:-Ternitrate of bismuth 995 grs.; citric acid 23 oz.; liq. ammoniæ and water q. 8.

It might have been an advantage if Mr. Tichborne's process had been given in the Pharmacopoeia instead of the present one, but this would have necessitated the introduction of the crystallized ternitrate as a distinct preparation, and the authors may have considered that confusion would arise if two nitrates of bismuth were officinal.-Pharm. Journ., March, 1868.

BLUE-BLACK WRITING INK.

A correspondent has sent us the following recipe for a blueblack writing-ink, which, he says, answers very well for a

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Macerate the galls and cloves in 20 ounces of the water for a week; decant the liquor, and add to the residue of the solid ingredients 10 ounces of the water, with which continue the maceration for four days; then decant as before, and repeat the maceration with the remaining 10 ounces of water for another period of four days. Mix now the whole of the liquors, recovering from the galls all that can be obtained by squeezing them in a cloth, and afterwards filter. To this add first the sulphate of iron, then the sulphuric acid, and lastly the indigo paste. Care must be taken that the indigo does not contain much free acid.Lond. Pharm. Journ., March, 1868.

IMPURITIES IN GLYCERIN.

To the Editor of the Chemical News.

SIR, The writer of the article on glycerin in Kunst and Geweberblatt is correct in attributing the acrid, irritating properties of some glycerin to the mode of preparation; but I have distilled glycerin which was quite as unsuitable for medicinal or surgical purposes as any spoken of. The volatile fatty acids. and ethers, which exist in crude glycerin, are sometimes condensed with the glycerin, and these have very irritating proper

ties.

In the glycerin which is made without distillation, the volatile acids, and ethers exist, but not in the same state as after distil

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