purpose. This apparatus is now placed over sulphuric acid until cool; its weight and that of the filter being known beforehand, the increase in weight is the weight of the uric acid on the filter, being the amount of uric acid contained in the amount of urine employed.

Volumetrical Analysis for Uric Acid.

This analysis has been introduced by Dr. Scholz, of Blankenburg-am-Harz, and is described at page 365 of Dr. Mohr's treatise.

Uric acid in an acid solution may be oxydized by a solution of permanganate of potash just as easily as the salts of the suboxyde of iron. Urea has no influence upon the permanganate, and cannot be oxydized any further in this manner. Creatine discolours a solution of permanganate of potash or chamæleon only after some time and in a higher temperature. Uræmatine has some influence upon chamæleon. In order to find and determine the equivalent of chamæleon for uric acid, the following experiments were made with a solution of chamæleon, the titre of which was: 1 cubic centimetre of solution of chamæleon = 0.045603 grammes of ammoniosulphate of suboxyde of iron. (This salt I shall hereafter describe under the name of the double salt of iron.)

I. 0201 grammes of crystallized air-dry uric acid were dissolved in caustic potash, and the solution was over-saturated with sulphuric acid. This solution required 23.9 c.c. of chamæleon = 1·0899 grammes of doublesalt of iron.

Doublesalt of iron × 0·18717 = uric acid.

II. 0-102 grammes of uric acid required 12·1 c.c. of chamæleon = 0·55179 grammes of doublesalt of iron.

Doublesalt of iron × 0.18189 = uric acid.

III. 0-323 grammes of uric acid required 36.9 c.c. of chamæleon = 1.6827 grammes of doublesalt of iron.

Doublesalt of iron x 0.19194 uric acid.

IV. 0-398 grammes of uric acid required 46 c.c. of chamæleon 1.6827 grammes of doublesalt.

=

Doublesalt of iron × 0.18972 = uric acid.

V. 0.278 grammes of uric acid

= 14638 grammes of doublesalt.

= 32.1 c.c. of chamæleon

Doublesalt of iron x 0.18990 = uric acid.

Leaving the second experiment, in which the quantity of

uric acid employed was too small, the average of the four other experiments is :

Doublesalt of iron x 0.18968 = crystallized uric acid. The equivalent of crystallized uric acid is 186, which divided by the multiplicator 0-18968, gives 980-59 doublesalt of iron. 186 parts of uric acid, therefore, take up as much oxygen as 980-59 parts of doublesalt of iron. Two equivalents, or 392 parts of the latter, take one equivalent or 8 parts of oxygen, consequently,

392: 8980·59 : x ; x = 20·012.

186 parts of uric acid, therefore, take 20·012 parts of oxygen, which is so little more than 20, that we can, without hesitation, assume the latter figure as correct. 20 parts are two and a half equivalents of oxygen, which would be taken by one equivalent of uric acid, or two equivalents of uric acid would take five equivalents of oxygen. If from 20 backwards we attempt the correction of the empirical figure 0-18968, we find

186
980

8:20392: 980, and =0·1897958,

which is very nearly019, instead of the empirical value 0-18968, which is also very nearly = 0·19.

Uric acid, in the form of a precipitate, is only slowly oxydized by solution of chamæleon. It is best to dissolve it in caustic potash, and after dilution to mix it with an excess of sulphuric acid. In that way uric acid is precipitated so slowly that it remains in solution during the experiment.

If 300 c.c. of urine are mixed with 5 c.c. of sulphuric acid, and allowed to stand for a few days, the uric acid is precipitated. We know already that this precipitate contains extraneous matters, uræmatine, which very nearly makes up for the loss of uric acid, from its imperfect insolubility in the acidified urine. The following experiments show these different relations quantitatively:

0.165 grammes of uric acid were dissolved in 300 c.c. of water by the aid of some caustic potash, and then precipitated by means of sulphuric acid and standing in the cold. 200 c.c. of the fluid were removed from over the precipitate and tested by means of chamæleon. They required 0·9 c.c. of chamæleon, which is equal to 0.00778 grammes of uric acid. This indicates that one part of uric acid is soluble in 25,707 parts of the acid fluid.

The precipitate of uric acid obtained was again dissolved

in caustic potash, the solution diluted to 300 c.c., and acidulated by means of 5 c.c. of sulphuric acid. 200 c.c. of the fluid, supernatant to the precipitate, again required 0·9 c.c. of chamæleon. In another experiment, 300 c.c. of the supernatant fluid saturated 1·4 c.c. of chamæleon. These results are sufficiently uniform.

In order to ascertain the amount of colouring matter which is inclosed in the crystals of a precipitate of uric acid from urine, 300 c.c. of urine were treated with 5 c.c. of sulphuric acid, and allowed to stand for twenty-four hours; the entire deposit required 36-3 c.c. of chamæleon. An equal quantity of urine was precipitated by sulphuric acid, the precipitate dissolved in caustic potash, diluted to 300 c.c., precipitated with sulphuric acid, and 200 c.c. of the supernatant fluid were tested with chamæleon. Of the latter there were required 2·6 c.c.; the entire 300 c.c. of fluid, therefore, would have required 3.9 c.c. of chamæleon. If we deduct of this 14 c.c., which were required for 300 c.c. of fluid, from a precipitation of pure uric acid, there remain 2.5 c.c. of chamæleon for the matters not being uric acid contained in the first uric acid precipitate from urine.

The second precipitate of uric acid was yet somewhat coloured, and, on repetition of the analysis, the chamæleon indicated foreign matters, not being uric acid, to the value of 1 c.c. of the solution. The supernatant fluid, from a fourth resolution and precipitation of the same uric acid only required as much chamæleon as the supernatant fluid from pure uric acid.

The total quantity of matters, not being uric acid, contained in the uric acid precipitate, amounted to about one tenth part of the whole. Put against this the loss from the imperfect insolubility, the excess becomes so very much reduced, that it is unnecessary to make any correction of the rough result found, and we may assume the two errors balancing each other, as we have done in the analysis of uric acid by weight.

In some cases the amount of foreign matter precipitated with uric acid may amount to one fifth of the entire precipitate. In this direction further researches are necessary.

Salts of Uric Acid-Urates.1

As uric acid is a bibasic acid, there are two different kinds of urates, the neutral and the acid salts. Of these, only the latter occur in urine, one equivalent of base being replaced by A. Bensch, Ann. d. Chem. und Pharm.,' liv, p. 189. Allen and Bensch, ibid., lxv, p. 181.

one equivalent of water, according to the following formula. M = metal.

ΜΟΥ

C1H2N ̧O,MO} = C12H ̧MNO, (Gerhardt).

101

All urates are either insoluble or only slightly soluble in

water.

Urate of ammonia. CH3(NH)NO.-This salt is always produced when uric acid and ammonia are allowed to act upon each other. When pure and dry it is a white amorphous mass, perfectly soluble in water, one part, however, requiring for solution 1608 parts of water at 77° F. (25° C.) .

Some authors state that urate of ammonia requires 2789 parts of urine for solution, and that the solubility is increased by the presence of a moderate quantity of saline matter. The solvent power of urine for urate of ammonia should be equal to that of pure water. But as no urine is quite free from urate of ammonia, and the latter cannot be separated without destroying the character of the former, it is very difficult, nay impossible, to determine the solvent power of urine for urate of ammonia, the more so as it is next to impossible, for practical purposes at least, to separate urate of ammonia from urate of soda. To saturate urine with urate of ammonia, and afterwards find the amount dissolved, is as yet an unsafe proceeding, because various causes may tend to increase the amount of ammonia found, which would have to be placed to the account of uric acid.

It may be obtained in small delicate needles by treating uric acid in boiling water with an excess of ammonia, or by dissolving uric acid in a warm solution of ammonio-phosphate of soda, and allowing the crystals to separate by rest. the latter case, the needles are united in groups, irregular or regular, presenting a star-like arrangement round a globule. The presence of urine prevents this form of crystallization. When crystallizing out of a solution in ammonia, it forms roundish, oval, or dumb-bell-like masses of a radiated structure and polarizing. This form is met with in the urine of birds. When appearing as a precipitate in alkaline (ammoniacal) urine, it forms very slender dumb-bells.' This form I have met with in perfectly black alkaline urine from a child suffering from dropsy after scarlatina. It was mixed with

Prout, On Stomach and Urinary Diseases,' 3d ed., pl. i, fig. 4. Ibid., i, figures of urate of NH3, as it occurs in the alkaline urine of hemiplegic, or paraplegic patients. v. Funke, Atlas,' taf. xiii, figs. 5 and 6.

rosettes and hexagonal plates of urate of soda, the deposit being perfectly black after filtration.

Urate of ammonia has, in a few instances of albuminous urine in dropsy after scarlatina, been observed in the form of spherules, with crystals of uric acid adhering to their surface. This appearance is illustrated in fig. 25 of Dr. G. Bird's work. I have succeeded in producing this deposit artificially. A patient having contracted a severe cold by exposure to rain and cold in one of our fashionable public gardens, discharged a large amount of perfectly white urate of ammonia in her urine, which was acid and of yellow colour. I allowed the deposit to subside towards the bottom of the vessel, and after having decanted the supernatant urine, redissolved the deposit by the application of heat. A concentrated solution of urate of ammonia in urine being so procured, some hydrochloric acid was added, and the mixture allowed to cool. A copious precipitate of spherules and granules of urate of ammonia soon formed, from the surface of most of which prisms and needles of uric acid began to crystallize. Under the continued influence of the acid, however, all the globules and granules of urate of ammonia were transformed into crystallized uric acid, the crystallization beginning with the formation of minute prisms, which gradually became larger and longer. The round and irregular bodies of urate of ammonia polarized faintly.

As a general rule, urate of ammonia, when occurring as a deposit, forms a dark, granular, perfectly amorphous precipitate. (Pl. III, fig. 2.) The granules may adhere to linear masses, or appear to form sausage-like bodies; the latter appearance is easily produced by rolling the thin glass cover of the object a few times to and fro, and has been erroneously described as a peculiar agglomeration of the urate.

To the naked eye these deposits of urate of ammonia appear as a subtle powder, varying in colour from absolute whiteness, through rose-colour, pink, brick-red, purple, and brownish-red. These colours are best observed after the deposit is collected on a filter.

The colour of urate of ammonia and of urates generally is caused by the adhesion to its particles of an abnormal colouring matter, urerythrine, Dr. G. Bird's purpurine. For this it has so great an attraction, that it may be used for separating urerythrine by dissolving, with the assistance of heat, repeated quantities of urate of ammonia, which, on cooling, will precipitate, carrying the urerythrine with them.

In diseases most commonly met with, the brick-red or pale fawn-coloured, so-called lateritious sediment is almost