38 On the Rapid Estimation of Urea. 
When it is desired to correct for temperature and pressure, by 
means of the usual formula, it is now necessary to disconnect E 
and f, and to pass the bulb of a small thermometer through f 
into the gas over the water in F'; after a minute or so the tem- 
perature may be read off and recorded, and the barometric read- 
ing made at the same time. In ordinary clinical experiments, 
however, the correction for temperature may be neglected when 
a thermometer in the room stands near to 52° F. The neighbour- 
hood of a fire or stove must be avoided in making the estimations 
of urea. 
In measuring the water expelled we may either read off the 
volume in drachms or sixths of a drachm; but since ordinary 
cylindrical two-ounce measures are rarely graduated to less than 
half drachms, the best plan is to pour the excess over a definite 
number of drachms into a tall two-drachm measure, bearing in 
mind that every ten-minim division represents the sixth of a 
drachm. | 
I tind as the result of a large number of direct experiments 
with a standard solution of pure urea, some of which will be given 
farther on, that one grain of urea produces sufficient gas at a 
tenvperature of 52° F. and a barometric pressure of 30:06 inches 
to expel 64th drachms of water, the volume of liquid in the 
bottle A being three drachms, and the hypobromite added, ten 
drachms. 
It may be mentioned that measures of capacity need not be 
employed in the determinations of urea, as the water expelled 
may be received in any suitable vessel which has been previously 
weighed. At the end of the experiment the vessel and expelled 
water are weighed. When the estimation was made under the 
conditions above named one grain of urea was found to expel, as 
a mean, 365 grains of water by weight. This number is easily 
remembered as it happens to be identical with the number of 
days in a year. 
Effect of the degree of dilution upon the determination of 
urea.—An apparently trifling observation led me to examine the 
effect of dilution upon the yield of nitrogen obtainable from a 
constant weight of urea, and the results arrived at are stated in 
the table given below. 
