URINE. 135 



The urine to be examined must be tested with litmus paper, 

 in order to ascertain the presence or absence of free acid. 

 Healthy urine is generally acid, seldom neutral. If the urine 

 is turbid, it must be examined under the microscope ; the pre- 

 sence of mucus can be the only cause of turbidity in healthy 

 acid urine. The specific gravity of the urine is best estimated 

 by the 1000-grain bottle. 



The quantity of urine to be analysed must be carefully 

 weighed, or the amount contained in the 1000-grain bottle (the 

 contents of which are exactly known when the stopper is in- 

 serted,) may be taken. A small portion always adheres to the 

 glass upon pouring it out, the quantity of which can be ascer- 

 tained by weighing. 



1. Determination of the free acid. 



A known quantity of warm urine must be treated with tinc- 

 ture of litmus in which the excess of free alkali has been neu- 

 tralized by acetic acid, so as to leave a perceptible red tint. 

 Dilute solution of ammonia must then be added by drops, and 

 with constant stirring, until the red colour begins to merge 

 into a blue. The quantity of ammonia required for this pur- 

 pose is estimated by weight, or, if a graduated vessel is used, 

 by measure. From our knowledge of the quantity of ammonia 

 in the solution, we can estimate the quantity of free lactic 

 acid. 



2. Determination of the water and vesical mucus. 



From 500 to 1000 grains of urine must be filtered ; the mucus 

 which remains on the filter must be washed with water, dried, 

 and weighed with the filter, the weight of which should have 

 been previously determined. The filtered urine must be eva- 

 porated in the water-bath to the thickness of an extract, and 

 then placed (in its basin) in a receiver over sulphuric acid, in 

 order to be thoroughly dried. The residue when dried must 

 be weighed with the basin, and the water estimated by the loss 

 of weight. 



3. Determination of the urea. 



The dry residue of (2) is moistened with a sufficient quantity 

 of water to reduce it to an uniform extract ; it is then thoroughly 



