49 



for an hour and then allow the ethereal or combined sul- 

 phates to settle. " Baryta mixture is prepared by making 

 saturated solutions in the cold of barium nitrate and barium 

 hydrate, and adding 2 volumes of the hydrate to one volume 

 of the nitrate. ' ' 



234. The phosphates consist of alkaline and earthy salts 

 in the proportion of 2 to i. The latter are insoluble in an 

 alkaline medium and are precipitated when acid urine be- 

 comes alkaline. They are insoluble in water, but soluble 

 in acids ; in urine they are held in solution by free COj. 

 The alkaline phosphates (sodium and potassium) are very 

 soluble in water, and they never form urinary deposits. 



The earthy pho.sphates are phosphates of calcium 

 (CajPOj)^ (abundant) and magnesium (MgHPO^ plus 

 jHjO) (scanty). The quantity is i to 1.5 grammes. They 

 are precipitated when the urine is alkaline, although not in 

 the form in which they occur in the urine. In normal 

 herbivorous urine the phosphates are said not to occur. 



235. To portions of the three clear filtered urines add 

 nitric acid, boil, and add barium chloride and boil again; 

 a precipitate of barium sulphate may be formed. Filter and 

 to the cool filtrate add ammonia ; a precipitate of barium 

 phosphate may appear. It is understood that the experi- 

 ments are to be made upon samples of all three urines and 

 any difference in their responsiveness to the tests is to be 

 recorded. 



236. The earthy phosphates have a clinical significance. 

 They are increased in osteomalacia and rickets, in chronic 

 rheumatoid arthritis after prolonged mental fatigue, and by 

 food and drink ; and they are diminished in renal diseases 

 and phthisis. 



The alkaline phosphates are chiefly acid sodium phosphate 

 (NaHjPO^) with traces of acid potassium phosphate 

 (KHjPOj). The quantity is from 2 to 4 grams and they 

 are derived chiefly from the food and perhaps a small 



