[ 290 ] 



XLIII. On a new Method for the Determination of Urea. By 

 John W. Draper, M.D., Professor of Chemistry and Physio- 

 logy in the University of New York*. 



THIS method depends on the fact, that urea in solution or 

 in urine is immediately decomposed by nitroso-nitric acid, 

 carbonic acid gas escaping with a brisk effervescence. 



In practice, therefore, the determination of urea is reduced to 

 the determination of carbonic acid, one of the simplest operations 

 of chemistry. 



It is to be recollected, that the carbonic acid thus set free will 

 always be contaminated with a certain quantity of nitrous acid 

 vapour; provision must therefore be made to exclude this 

 source of error. In a series of experiments which I have been 

 recently making on the constitution of urine, I have resorted to 

 several different methods, but upon the whole have preferred to 

 determine the urea as carbonate of baryta. 



As at the present time the attention of physicians is closely 

 directed to variations in the composition of the urine, and new 

 methods have been published by Liebig and others, the details 

 of this one may perhaps be acceptable. To the chemist, what I 

 have already stated has made it intelligible. 



Preparation of the Decomposing Liquid. — The substance em- 

 ployed for the decomposition of the urea is nitroso-nitric acid. 

 It may be made by passing into strong nitric acid, kept cold by 

 immersion in ice-water, nitrous acid arising from the decompo- 

 sition of nitrate of lead by heat. The liquid assumes after a 

 while a green colour, and evolves dense red fumes ; it is then 

 fit for use. But as this process is somewhat troublesome, I 

 prefer the following. 



Take a single cell of Grove's voltaic battery, placing as usual 

 dilute sulphuric acid in contact with the amalgamated zinc, and 

 strong nitric acid in the porous cup in contact with the platinum. 

 Connect the zinc and platinum together. The nitric acid soon 

 begins to change colour by dissolving nitrous acid, and in a few 

 minutes becomes green. It is then decanted for use. 



Determination of the Urea in Urine. — Filter a portion of urine 

 from the mucus it contains. The object of this is to prevent 

 subsequent frothing. 



In a bottle, a, fig. 1, of about 50 cubic centimetres capacity, 

 place 5 grammes of filtered urine. Through the cork which 

 closes the mouth of the bottle a small funnel tube, b, passes down 

 to the urine. Through this, when everything is ready, the 

 nitroso-nitric acid is poured. There passes likewise through 



* Comirfunicated by the Author. 



