434 URINE. 



oxalate of ammonia, (provided the urine be acid,) and after the 

 oxalate of lime has been washed according to the usual methods 

 of analytical chemistry, to expose it to a red heat, weigh it, and 

 thus calculate the quantity of the lime. If we precipitate acidified 

 urine with a baryta salt, we may approximately determine the 

 ..quantity of sulphuric acid ; but if we follow all the prescribed rules, 

 we shall, after exposure to a red heat, obtain a carbonaceous sul- 

 phate of baryta, which after the combustion of the carbon will 

 exhibit an alkaline reaction or develop bubbles of air, when treated 

 with acid. A similar remark may be made in reference to the 

 determination of the chlorine in the urine by direct precipitation. 



The method of determining the potash in the urine by bichlo- 

 ride of platinum would, for reasons which remain to be explained, 

 be almost equally devoid of exactness with the modes of determi- 

 nation already referred to. 



It must be observed in reference to the qualitative investiga- 

 tion of the urine, that it is very instructive to allow this fluid to 

 stand for a prolonged period, and to examine it from time to time 

 with the microscope, since the nature of the physical alterations, 

 the rapidity with which they occur, and the changes observed in the 

 reaction on vegetable colours, yield, as we have already seen under 

 the head of Urinary Fermentation, considerable information as to 

 the presence of such ingredients or characters of the urine as 

 could not be chemically detected. 



More importance has been attached to the determination of 

 the specific gravity of the urine than it actually possesses in a 

 scientific point of view, or than it merits from the methods em- 

 ployed in determining it. In fact, the determination of the specific 

 gravity of the urine is of less importance than that of any other 

 animal fluid. We may regard it almost as a law, that the blood, 

 and most other animal fluids, have always a tendency to maintain 

 a definite specific gravity, which is necessary for the fulfilment of 

 their functions. The fluctuations in the specific gravity of these 

 fluids are, therefore, very inconsiderable, and hence it is the more 

 important to notice great variations in them. The case is altogether 

 different in respect to the urine, whose concentration is almost in- 

 variably changing ; indeed, it seems to be the special function of the 

 kidneys to maintain the other animal juices in their normal state of 

 admixture and in their proper degree of concentration ; at one 

 time there being an excess of salts carried off with the detritus 

 arising from the metamorphosis of tissue, at other times, more or 

 less water. We have already shown what numerous and different 



