5G8 Proceedings of the Iioyal Society 
or hot acidulated water, requires a dilution of the blood with 
several volumes of water as we have seen ; worse than this the 
alcoholic or watery extract of urea thus obtained contains so many 
extractives that the urea passes through several processes before 
it is in a fit condition to estimate, loss occurring during each 
process. 
Can we lessen or altogether prevent this loss is the question 
before us ? 
Hearing that tungstic acid does not precipitate urea, and knowing 
also that it precipitates most organic substances, I tried to separate 
the urea by this agent. 
Diluting with only f vols. it was possible very completely to 
separate the albumens as a fine granular mass by the addition of 
tungstate of soda and acetic acid. 
The after process, however, was so complicated (the urea had to 
be separated from the tungstic acid, and acetate of soda, and many 
extractives) that the loss was as great as before. 
The separation by dialysis had long been thought of, for it 
was naturally suggested by the epithelium of the kidneys, 
by which urea is separated during life from the blood. 
It had not been tried, however, as it promised to be tedious. 
Hearing, however, from Professor Browne that by placing blood 
into a dialyser with alcohol in the outer vessel it became quite hard 
and dry in a few hours, encouragement was given to a trial of this 
method. 
Urea being very soluble both in alcohol and water, it would 
probably pass out with the fluid parts of the blood into the alcohol ; 
a trial proved this to be the case, and a few experiments sufficed to 
found the method which will now be described. 
80 c.c. or 100 c.c. of defibrinated blood are placed within a 
dialyser so as to form a thin layer on the parchment paper. The 
dialysers that I use are of glass, the inner vessel having a diameter 
of 8 to 9 inches, the outer one-half or three quarters of an inch 
more. The blood must not form a layer more than about 3 mm. 
thick, otherwise the lowest stratum will become dry and imper- 
vious while the upper will still remain fluid. 
One hundred c.c. of alcohol are poured into the outer vessel, 
and the whole is covered. In from four to eight hours the alcohol 
