THE COMPOSITION AND CHARACTERS OF THE URINE 1163 



Sulphates. The salts of sulphuric acid do not form an important con- 

 stituent of the food. The sulphates of the urine are derived almost entirely 

 from the oxidation of the sulphur of the protein molecule. The output of 

 sulphates is therefore, like that of urea, an index of protein metabolism. 

 As the nitrogen of the urine goes up, so the sulphates will increase. On an 

 average diet the ratio of urinary nitrogen to S0 3 is about 5:1; though, 

 owing to the varying content of different proteins in the sulphur, this ratio 

 will alter with the nature of the protein taken as food. The daily 

 output of sulphuric acid varies between 1-5 and 3 grm. S0 3 . The greater 

 part of the sulphate is present as sulphates of the alkaline metals. A certain 

 proportion, about 10 per cent., is present in the form of conjugated or 

 ethereal sulphates, chiefly indoxyl sulphate. A small proportion of the 

 sulphur excreted in the urine is present in unoxidised form as so-called neutral 

 sulphur. The neutral sulphur probably includes a number of different 

 bodies, among which sulphocyanates and cystine are the best known. 



Inorganic sulphates can be precipitated from the urine by the addition of hydro- 

 chloric acid and barium chloride. On filtering off this precipitate, the filtrate contains 

 the ethereal sulphates. On boiling, the hydrochloric acid decomposes these substances, 

 setting free sulphuric acid, which combines with the excess of barium present and is 

 precipitated as barium sulphate. This second precipitate therefore, when weighed, 

 gives the amount of ethereal sulphates present. To determine the neutral sulphur, the 

 fluid after the separation of both kinds of sulphates is treated with sodium carbonate 

 to precipitate the barium, filtered, and the filtrate evaporated to dryness. The residue 

 is then ignited with potassium nitrate, cooled, and extracted with water. By this 

 treatment all the neutral sulphur is converted into sulphates, which can be thrown down 

 from the solution with barium chloride and weighed in the usual way. 



Phosphates. The phosphates of the urine are derived partly from the 

 phosphates of the food, partly from the oxidation of the organic phosphorus- 

 containing constituents of the food and of the tissues, e. g. nuclein, lecithin, 

 etc. If the food contains much calcium and magnesium, the amount of 

 phosphates excreted by the urine diminishes, since these substances are 

 excreted with the faeces as calcium and magnesium phosphates. According 

 to the diet therefore, phosphoric acid may be excreted either by the intestine 

 or by the kidneys. The amount of phosphates, reckoned as P 9 5 , excreted 

 in the course of the day may vary between 1 and 5 grm. In the urine the 

 phosphates exist as a mixture of the mono- and di-sodium phosphates, the 

 relative amounts of the two varying with the acidity of the urine. If the 

 urine is neutral or alkaline there is very often a deposit of earthy phosphates. 

 Whether this deposit is present or not depends on the varying solubility of 

 the different calcium and magnesium phosphates. Thus the mono-mag- 

 nesium phosphate MgH 4 (P0 4 ) 2 and the mono-calcium phosphate CaH 4 (P0 4 ) 2 

 are both fairly soluble in water, and their solubility is increased by the 

 presence of neutral salts. With increased acidity of the urine the proportion 

 of the two bases present in these forms is diminished. The di-magnesium 

 and di-calcium phosphates are only slightly soluble in water, and the latter 

 would, if present in the urine, be deposited. One may indeed, in slightly 

 acid urine, find the di-calcium phosphate occasionally present as a crystalline 



