68.2 
UREA IN THE URINARY SECRETIONS. 
error ; the principal one being, that ammonia, if it exists in 
the urine, gives rise to nitrogen, and, therefore, increases the 
apparent amount of urea. But the same objection holds 
equally in Liebig’s and Kagsky’s methods, which are, per- 
haps, the two most accurate at present known. Uric acid, 
also, is similarly affected by the hypochlorite, but it and 
ammonia ordinarily occur in such small proportion in urine, 
that the error produced would be but trifling, and is partly 
corrected by taking the calculated quantity of nitrogen, which 
is, as I have shown, something more than that derived from 
a certain quantity of urea by direct experiment. 
In cases where ammonia or uric acid occurs in more than 
ordinary quantity, these substances must be separated by 
the usual means employed, before having recourse to my 
method. 
I should think that gently heating the urine with a certain 
quantity of baryta water, as long as the odour of ammonia is 
disengaged, and then filtering the solution, as recommended 
by Liebig, for the separation of ammonia before applying his 
method {see the ‘Journal of the Chemical Society? vol. vi. page 
30) would effect the object very easily, and separate not only 
the ammonia, but also the greater part, if not all, of the uric 
acid present. 
There is one other source of error which may arise, and 
which can easily be avoided ; it is the following : that if a solu- 
tion of hypochlorite of soda alone, or standing over mercury, 
be exposed to the light for several days, it will very gradually 
evolve a very minute quantity of oxygen. So that the 
experiment in determining urea should not be carried on for 
too long a time, but a day, or even two, will scarcely make 
any appreciable effect on the quantity of gas evolved in 
testing the urea. 
The reaction which appears to take place in the process 
seems to be the following : the hypochlorite of soda reacting 
on the urea gives rise to nitrogen, water, carbonic acid, and 
chloride of sodium : — 
Urea. 3 Hvpochlorite Soda. 
Thus, C 2 H 4 N 2 0 2 + 3 (ClO-NaO) 
= N 3 + 2 CO a + 4 HO + 3C1 .Na. 
The nitrogen is evolved and the carbonic acid i3 absorbed 
by some of the hypochlorite of soda in excess, for I find that 
this salt absorbs carbonic acid very quickly, without evolving 
any other gas, and I have failed in several experiments to 
detect the smallest portion of carbonic acid gas in the gas 
produced by acting on urea, though I have always noticed 
