248 PROFESSOR LIEBIG ON THE AZOTIZED 
water ; the liquid albumen of the blood may be mixed with any 
quantity of water, and the albumen of the egg is soluble in water. 
Fresh prepared fibrin has the form of transparent, soft, elastic 
threads, which are not at all glutinous, and cannot be united by 
kneading. When a solution of albumen is heated to a certain 
temperature, it coagulates into a white, soft, elastic mass, which 
cannot be kneaded. Albumen is not precipitated from its solu- 
tion in water by acetic acid. The casein of the milk of animals, 
which is the chief nourishment of their young, is also distin- 
guished from fibrin, by solubility in water. Heat does not coa- 
gulate the solution of casein like that of albumen, but a pellicle 
is formed by evaporation on the surface of the former solution, 
which, if removed, is continually renewed. Casein also is pre- 
cipitated from solution by acetic acid, as a thick, coherent mass, 
or curd. Fibrin, albumen, and casein, comport themselves in 
the same manner with hydrochloric acid. They are dissolved 
by that acid with the aid of heat ; and if the solution is exposed 
to a somewhat high temperature for a length of time, it assumes 
first a beautiful lilac, and then a violet blue colour. At this 
point of the decomposition, carbonate of ammonia, and other re- 
agents, act in the same manner in all the three solutions. 
Fibrin, albumen, and casein, possess the same composition, 
according to all the analyses hitherto made ; and these analyses 
have been so often repeated, that no doubt can be entertained 
of the accuracy of the chief results. The proportion of organic 
elements being the same, they must be arranged in a different 
order, to account for the difference in properties of these prin- 
ciples. The gas obtained by burning any of these three sub- 
stances with oxide of copper, in the ordinary process of analysis, 
is found to be a mixture of nitrogen and carbonic acid. When 
executed according to the qualitative method, in which relative 
quantities only are obtained, 8 volumes of the gas gave very 
nearly 7 volumes of carbonic acid, and 1 volume of nitrogen. 
When analysed so as to ascertain absolute quantities, or accord- 
ing to the new method of Drs. Will and Varrentrapp, by esti- 
mating the ammonia obtained from them, the atomic proportion 
was found to be as 8: 13; or these bodies give 8 volumes of car- 
bonic acid to 1 volume of nitrogen. 
The proportion of carbon obtained, when these substances are 
burnt with oxide of copper, is smaller, because it is difficult to 
cause them to undergo complete combustion; but if chromate 
