of Edinburgh, Session 1879-80. 
569 
in tlie outer vessel has risen, being increased in volume by the 
fluid parts of the blood, which now forms a dark tough cake within 
the dialyser, which, as a rule, sticks to the parchment paper. Of 
course this contains still much urea, and it must be washed. It is 
not sufficient to pour fresh water upon it ; it must be detached from 
the parchment paper and bruised with fresh water in a mortar. 
For this purpose the parchment paper with the blood attached is 
brought into a flat dish gently heated over a water bath, when the 
blood may be detached with the help of a little warm water. 
Fresh parchment paper is now placed upon the ring of the dialyser, 
and the bruised mass brought into it and placed again in the 
alcohol. The blood soon becomes dry again from abstraction of 
water, and the alcohol is now evaporated after acidification with 
oxalic acid. 
The blood in the dialyser is now warmed to drive off the little 
alcohol that is mixed with it, and is replaced in the dialyser with some 
more water, with which it can now be mixed with a curved spatula ; 
for now it forms a finely granular mass, and does not cling to the 
parchment paper. When this is dry it is washed in the same way 
for the last time. 
The alcohol here is also evaporated and the residue extracted 
with a little alcohol which is evaporated. An all-important 
point is this, that mixed with the' urea, which may even now be 
seen on the dish, there is but little organic matter. Most of this 
can now be removed by washing the residue with petroleum 
naphtha. It is then extracted with acetic ether and the urea 
estimated. 
I accomplished this in Germany by a method introduced by 
Bunsen ; the urea is heated with an ammoniacal solution of chloride 
of barium in sealed tubes at 200° C. ; decomposition of the 
urea into ammonia and carbonic acid occurs, and the amount of this 
is determined by weighing the carbonate of barium which is 
formed. 
Lately I have used a shorter and more suitable method intro- 
duced by Huefner. The urea is mixed with a solution of hypo- 
bromide of soda, when carbonic acid and nitrogen are formed. The 
latter is collected, and the quantity calculated where the amount of 
urea may be inferred. There is loss with this process of about 
vol. x. 4 a 
