UREA IN THE URINARY SECRETIONS. 
681 
pharmacopoeia, under the name “ Sodae Chlorinatae Liquor,” 
and therefore can be so easily procured ; whereas the potash 
salt, not being used in medicine, would require to be specially 
made for this purpose. As to the hypochlorite of lime I do 
not think it so effectual, and it has the disadvantage of soiling 
the sides of the graduated tube by the carbonate of lime 
formed in the reaction. In reference to the quantity of 
hypochlorite of soda to be used, it should always be employed 
in excess, and I think that about five or six times the volume 
of urine employed would be found generally to be quite 
sufficient, and ensure there being an excess. 
The amount to be used may be easily determined by direct 
experiment, by adding to a certain quantity of urine to be 
examined, in a small glass, a measured quantity of the hypo- 
chlorite, and leaving it for a short time till the evolution of 
gas is nearly over ; then if, on the addition of more of the 
hypochlorite, the effervescence is renewed, it shows that there 
was not enough of the decomposing liquor first employed, 
and more must be added till there is no further evolution of 
gas produced, and the quantity of hypochlorite which is 
required to arrive at this point indicates the amount neces- 
sary. I found by experiment that one grain of urea requires 
somewhere about half a fluid ounce of the ordinary Sodae 
chlorinatae liquor for its complete decomposition. 
The amount of mercury employed requires some little 
attention ; it should, as a general rule, be never less than 
the volume of gas evolved, for if the volume of gas produced 
is more than that of the mercury employed, it will be more 
than that of the solution of salt, and therefore some of the 
mixture of urine and the hypochlorite will be forced out of 
the tube before it is completely decomposed, and consequently 
some of the gas will be lost ; so that if this occurs we must 
repeat the experiment, using either a larger quantity of 
mercury, if our tube will allow, or diminishing the quantity of 
urine employed. It might be supposed, on first sight, that 
this method would be liable to the following source of error, 
viz. — that some of the gas would be evolved and lost during 
the pouring in of the hypochlorite ; but this is not the case, 
as several seconds elapse before there is any apparent reaction 
or evolution of gas on mixing the hypochlorite with the 
urine, and therefore giving full time to perform the experi- 
ment without loss of any gas. 
I have, also, ascertained that the ordinary acid reaction of 
the urine does not affect my method. 
I should observe, that this new method, like all the others 
known, is not perfectly free from some slight sources of 
