1888 - 89 .] Haycraft and Duggan on Coagulation by Heat. 383 
the coagulation point is being continually raised, both in virtue of 
the albumen becoming more dilute and in virtue of its becoming 
less acid ; these factors bring the coagulation to a standstill, but, 
after filtering off the coagulum, if the fluid be brought back to its 
original degree of acidity, and heated to the same temperature, 
coagula will again form, unless the albumen has undergone some 
physico-chemical change. 
It follows, too, that it is impossible to separate two albumens from 
one another by heat coagulation, unless, during the process of 
coagulation, the degree of acidity is kept uniform by the addition of 
small quantities of fresh acid, and unless the coagulation point of 
the most dilute solution of one of the albumens present be below the 
coagulation point of the other albumen. We became more con- 
vinced of this, when repeating in detail the experiments on fractional 
coagulation. After keeping an albuminous solution, either egg or 
serum albumen, at the temperature at which flocculi appear, for five 
or six minutes, and then filtering off the flocculi, we found that fresh 
flocculi appeared, when the filtrate had been re-acidified, and again 
raised to the same temperature. Two or three crops might be thus 
removed in the case of egg-white. Keeping up the same degree of 
acidity, and raising the temperature, we were able to get other crops 
of albumen. We were struck, however, by the fact that, while 
dealing with the more dilute albumen, the coagulation took place 
with difficulty, and it was longer delayed. This was particularly 
the case with egg-albumen. If the fluid filtrate from the coagulated 
flocculi be divided into two parts, and one portion raised gradually 
in temperature, opalescence followed by the formation of flocculi 
will appear. If the other portion be raised in temperature and 
kept for, say, three minutes at a temperature one or two degrees 
below the temperature at which opalescence appeared in the first 
portion, it will become opalescent and perhaps form flocculi. 
We found, in fact, that it was impossible to get the subsequent 
coagulation at definite points, as indicated by the previous observers, 
for the coagulation point depended upon the way in which the 
operations had been carried out. This was especially the case, when 
dealing with egg albumen, and we have little doubt that MM. 
Corin and Berard, working with careful method, invariably raised 
their temperatures to points which perhaps their first experiments 
