48 



231. Chlorides are chiefly those of sodium with a little 

 potassium and ammonium, derived chiefly from the food and 

 amount to an average of 12 grams daily. 



Test a portion of each urine with a few drops of silver 

 nitrate solution. A white, cheesy or curdy precipitate in 

 lumps insoluble in nitric acid indicates the presence of silver 

 chloride. The phosphate of silver may also be thrown down 

 but this is soluble in nitric acid. In acute cases of pneu- 

 monia the chlorides may be absent from the urine, their re- 

 appearance in the urine is a good .symptom. In normal 

 urine the amount of sodium chloride remains quite con.stant, 

 about 0.75%. A few drops of urine evaporated upon a slide 

 will give octahedral or rhombic crystals, a compound of 

 sodium chloride and urea. 



232. Sulphates. The sulphates are chiefly those of sodium 

 and potassium. The total quantity of sulphates is 3 to 4 

 grams daily. Only a small amount of them enters the body 

 with the food, so that they are chiefly formed from the 

 metabolism of proteids in the body. They have no clinical 

 .significance. Sulphuric acid, however, exists in the urine 

 not only in combination with alkalies as stated above as 

 " preformed sulphuric acid " but also with organic radicles, 

 phenol, skatol, etc., forming " ethereal sulphates " or " com- 

 bined sulphuric acid ". The latter forming about i/io of 

 the total sulphates, and, originate from putrefactive pro- 

 ce.sses in the intestine. 



After acidulating with hydrochloric acid to prevent the pre- 

 cipitation of phosphates, add to a small part of each urine, a 

 little 2% barium chloride, a white heavy precipitate of 

 barium sulphate is formed, insoluble in nitric acid. 



233. To separate the combined (ethereal) sulphuric acid. 

 Mix 50 cc. of omnivorous urine with an equal bulk of 

 "baryta mixture". Stir and filter. This removes the 

 ordinary sulphuric acid as sulphate of barium. Add 10 cc. 

 of hydrochloric acid and keep in the water bath at 100° C. 



