567 
of Edinburgh, Session 1879 - 80 . 
My first endeavour was to find a liquid in which urea is insoluble. 
A number were tried, and at last a substance, petroleum naphtha 
(a naphtha lately imported from America, and which is sold with 
other naphthas under the name of benzoline), was found in which 
urea is quite insoluble, and by means of which it is possible to 
separate urea from oil when both are in alcoholic solution. This 
petroleum naphtha, or benzoline, as we shall afterwards see, is of 
great service. 
An endeavour was now made to prevent or lessen the loss which 
occurs on evaporating a solution of urea. 
It was thought that possibly the high temperature used was 
prejudicial, and accordingly evaporations were conducted with 
solutions of known strength at a temperature lower than is ordinarily 
used. The solutions were evaporated on a water bath in flat dishes 
at a temperature of from 40° to 50° C., but, unfortunately, this 
was of little avail, the difference in the result being but very 
slight. 
Failure also resulted when the urea solution (not an artificial one) 
was evaporated at a very low temperature and with diminished 
atmospheric pressure. The solution was acidified with acetic acid 
with loss following its evaporation. 
Urea forms with acids salts of definite composition, and of well- 
marked crystalline form. 
It was thought that by changing this substance into an oxalate 
or nitrate these might prove more stable, and as the ordinary 
methods admit of their estimation in these forms, the process 
might succeed, or at any rate it would be easy to reduce them as a 
last step into urea again. 
A partial success was the result of this trial ; for on evaporating 
an alcoholic solution of oxalate of urea (0T gramme per litre) there 
was not quite 2 per cent. loss. Indeed, a certain degree of decom- 
position seemed inevitable, and no way was found out of the diffi- 
culty. Uo method which involved evaporation could be said to be 
perfectly accurate. It is still possible to reduce this loss by using 
as little fluid as possible, and to obtain the urea unmixed with 
other organic solids, the presence of which is so prejudicial to the 
accuracy of our results. 
To separate the albumen from blood, either with boiling alcohol 
