ELEMENTARY PHYSIOLOGICAL CHEMISTRY 263 



EXPERIMENT II. To detect the Total Phosphates. Add to urine an 

 equal bulk of nitric acid, and then half its bulk of an acid solution of 

 ammonium molybdate ; warm to 55 C. ; a yellow crystalline precipitate 

 of ammonium-molybdo-phosphate separates out. 



EXPERIMENT III. To separate the Earthy from the Alkaline Phos- 

 phates. Make urine alkaline with ammonia, and allow to stand for 

 about half an hour. A white precipitate of calcium and magnesium 

 phosphates settles down ; filter, dissolve the precipitate in nitric acid, 

 and add to this solution some molybdate of ammonium and warm a 

 yellow precipitate results. 



Most of the urinary phosphates come from the food, but a certain 

 proportion is derived from the metabolism of nuclein. In order to 

 determine these nuclein phosphates, it is necessary to estimate the 

 amount of free phosphates given in the food, and then to deduct this from 

 the amount excreted in the urine and faeces, and the difference (i.e. the 

 excess excreted to that administered) corresponds to that derived from 

 the decomposed nuclein. If the alloxuric bodies be simultaneously 

 estimated, it will be found that their amount bears a constant ratio to 

 that of the phosphates, since they are both derived from the same 

 source. 



Sulphates. These have a bitter taste, in consequence of which they 

 are not taken to any extent in the diet, so that those excreted in the 

 urine are derived from the sulphur of broken down tissue proteid. It 

 will be remembered that proteid contains 1 per cent. S and 16 per cent. 

 N, and, if it be true that both these elements in the excreta represent 

 end products of proteid metabolism, a similar ratio should exist in the 

 urine. This is approximately the case, the ratio of H 2 S0 4 to N being 

 about 1-6. l A determination of the sulphates provides us, therefore, 

 with a very valuable control in estimating proteid metabolism, and is, 

 indeed, the only means by which we can determine the influence of non- 

 proteid nitrogenous bodies on the metabolism of tissue proteid. About 90 

 per cent, of the sulphuric acid is excreted in combination with alkalies 

 the inorganic sulphates ; and about 10 per cent, in combination with 

 organic bodies absorbed from the intestine the ethereal sulphates. 



EXPERIMENT IV. To about 5 c.c. of urine add an equal bulk of 

 alkaline barium chloride solution (a mixture of 2 vols. Ba(OH) 2 and 

 1 vol. BaCl 2 ). A precipitate of barium sulphate separates out. This 

 corresponds to the inorganic sulphates. Filter, acidify the filtrate with 

 hydrochloric acid, and boil a second precipitate, not so marked as the 



1 Theoretically, the ratio should be a little over 1-5, some of the S being 

 contained in the urine, not as sulphates, but organically bound up in such bodies 

 as cystin. 



