II. 



ANALYSIS OF THE URINE. 



i. DETERMINATION OF UREA ACCORDING TO LiEBio. 1 



(a) Preparation of the Solution. 



Dissolve 43 g. of yellow oxide of mercury (hydrargyrum 

 oxydatum flavum via humida paratum, the red oxide can- 

 not be used) in a mortar in a mixture of 100 cc. of nitric acid 

 and the same amount of water. Place the solution together 

 with the mercuric oxide, which still remains undissolved, in 

 an evaporating-dish, heat on the water-bath, evaporate to a 

 thin sirup, let cool, and dilute gradually with small portions 

 of water to a volume of 550 cc., let stand till next day and 

 filter through a dry filter. 



(6) Standardizing the Solution. 



For this purpose an exactly 2 per cent, solution of urea is 

 required. Test the purity of the purest possible urea that 

 can be obtained. The aqueous solution should not give any 

 turbidity with nitric acid and silver nitrate solution, nor with 

 hydrochloric acid and barium chloride solution; it should 

 give no ammonia when boiled with a solution of sodium car- 



1 This method, which gives approximately the total amount of nitro- 

 gen in the urine, expressed as urea, is regarded by many as out of date. 

 Moreover, it cannot be compared with the Kjeldahl method in accuracy. 

 It is, however, simpler than the Kjeldahl determination and does not 

 necessitate a complete laboratory, as the mercury solution can be bought 

 and only needs to be tested. It is therefore still a valuable method. 



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