URINE. 467 



mach and the urine passed for five consecutive days. Some 

 days the urine exceeded the drink ; but upon the whole, the 

 drink was to the urine nearly as eleven to ten. On one day the 

 drink was to the urine as 100 I 68-2, on another as 73 I 102-02. 

 If the induction were sufficient, it would follow that the drink 

 exceeds the urine by one-tenth part. Hence if the mean quan- 

 tity of urine voided by 2-913 Ibs., that of the drink will be 3-204 

 Ibs. Chossat states that in his very numerous trials, the average 

 quantity of drink was to that of the urine as ten to nine nearly. 

 Varying somewhat according to the temperature, the quantity of 

 urine being greatest in the coldest weather. 



The number of times that urine is voided in twenty-four hours 

 varies greatly in different individuals. I know an individual who 

 enjoys good health, and who passes urine at an average only three 

 or four times a-day. The greatest number of times in the pre- 

 ceding tables is fourteen times and the smallest nine times. 



When urine is voided from a person in perfect health, it al- 

 ways contains an uncombined acid ; for it reddens litmus-paper, 

 and the change is permanent, and therefore not owing to carbo- 

 nic acid. Various opinions have been stated respecting the na- 

 ture of this acid. Proust and Fourcroy and Vauquelin suppos- 

 ed it to be the phosphoric. Urine contains a small quantity of 

 phosphate of lime, which may be precipitated from it by by caus- 

 tic ammonia. Now, as phosphate of lime is insoluble in water, 

 while a little of it is actually held in solution in urine, it was not 

 unreasonable to conjecture that it was in the state of biphosphate 

 of lime, which is slightly soluble in water, and capable of red- 

 dening litmus -paper. But a very simple experiment is sufficient 

 to show that urine contains no biphosphate of lime. Evaporate 

 urine to dryness, and ignite the residue. The residual salts do 

 not act on litmus-paper. Hence the free acid must be volatile, 

 since it is dissipated by a red heat. 



Berzelius affirms that urine contains lactate of ammonia and 

 free lactic acid. I have not been able to verify this statement 

 by experiment ; the quantity obtained being always too small 

 to enable me to investigate its nature. I mixed sulphuric acid 

 with fresh urine till it tasted distinctly acid, and distilled over a 

 third of the mixture from a glass retort, by means of a gentle 

 heat. The liquid thus obtained was tasteless, and had no per- 



