250 PROFESSOR LIEBIG ON THE AZOTIZED 
coagulate. Acids cause a precipitate in its solution which is so- 
luble in ammonia, but insoluble in dilute acetic acid. 
Vegetable casein is obtained from leguminous plants, such as 
beans, peas, and lentils, in the following manner :—warm water 
is poured over them, and they are allowed to soften for some 
hours, until they can be rubbed in a mortar to a syrupy con- 
sistence. Five or six volumes of water are then poured upon 
the mass, and the whole is thrown upon a fine sieve, through 
which the solution of vegetable casein flows, mixed with starch. 
It is now allowed to stand an hour, or two, till the starch is de- 
posited. 
The liquid which contains the vegetable casein in solution is 
then drawn off from the starch; it is not clear, but milky, and of 
a yellowish tinge. This cloudiness arises, partly from an admix- 
ture of fatty or waxy substances, and partly from a continued 
precipitation of the vegetable casein; a few drops of ammonia 
make the liquid somewhat clearer. 
The substance of leguminous plants, finely pulverized and 
washed in cold water, has no action on vegetable colours ; but 
if allowed to stand for some hours in water, it becomes slightly 
acid; this is the cause of the cloudiness of the last solution, and 
of the precipitation of the casein prepared from these plants. 
Boiling does not cause the slightest coagulation in the solution 
of vegetable casein; but a skin is formed on the surface of the 
liquid when evaporated, and is renewed as often as we remove 
it, exactly as in heated milk. 
All acids, without exception, coagulate the solution; it be- 
comes flocculent and of the consistence of jelly on the addition 
of acetic acid, which acid, even in excess, cannot dissolve coagu- 
lated vegetable casein. Tartaric and oxalic acid, in excess, dis- 
solve the precipitates which they cause. Sulphuric and nitric 
acids precipitate the last solutions anew. The casein of milk 
comports itself exactly like vegetable casein ; it is coagulated by 
acetic, tartaric and oxalic acids, the precipitate is dissolved in an 
excess of the latter two, and reappears on adding sulphuric or 
hydrochloric acid. 
An acid reaction is observable in all the precipitates of vege- 
table casein produced by acids; they are, in fact, compounds 
formed with the acids, and react in every respect as the corre- 
sponding combinations of the casein of milk. Alcohol also co- 
agulates it as it does milk. When the solution of vegetable 
