40 On the Rapid Estimation of Urea. 
tolerably regular, as the volume of nitrogen is diminished by 3th of 
a drachm (nearly) for each drachm of water added to the urea in 
the decomposition vessel A. 
The loss of nitrogen referred to is, doubtless, due in part 
to solution of the gas, but it is chiefly attributable to the 
regular diminution of the strength of the oxidizing agent used— 
the hypobromite solution—and to a corresponding increase in the 
extent of the secondary changes which are known to occur in 
the diluted liquids, and which involve a loss of gaseous nitrogen. 
Much of the error arising from the latter cause is avoided by 
adopting the plan of employing a constant volume of liquid ; 
hence the recommendations already made that two drachms of 
urine should be measured into the bottle A, and the measure 
rinsed out with not more than one drachm of water. The total 
bulk of liquid in A ought then to measure as nearly as possible 
three drachms. Eyen when the sample to be tested is measured 
with a pipette, it is well to add one drachm of water from an 
ordinary measure in order to bring up the total volume of liquid 
to the amount recommended. 
When the simple precautions are taken which I have already 
mentioned, the little apparatus described in this paper will enable 
a considerable number of estimations of urea to be made with 
rapidity, and with sufficient accuracy for ordinary clinical pur- 
poses. When very precise determinations are required, Liebig’s 
process must be resorted to, as all the methods in which hypo- 
bromites or hypochlorites are employed are liable to the errors 
pointed out above ; the accuracy of the results are also affected by 
theaction of the re-agent used on uric and hippuric acids, creatinine, 
and other nitrogenized compounds. On the other hand, when we 
desire to ascertain the total amount of nitrogen excreted by the 
kidneys, it is necessary to resort to the precise method of esti- 
mation which I communicated to the Surgical Society of Ireland.* 
Estumation of Urea by direct determination of the Nitrogen gas 
evolved by Sodic Hypobromite. 
The piece of apparatus now to be described was exhibited at a 
meeting of the Scientific Club in 1871, and has proved most useful 
* Vide Medical Press and Circular, May 18th, 1874, p. 402. 
