ANALYSIS OF VEGETABLE MILK. 08 



assumes at first the appearance of an agate with milky 

 clouds ; and it seems as if organic membranes were forming 

 under the eye of the observer. When the coagulum extends 

 to the whole mass, the yellow spots again disappear. By 

 agitation it becomes granulous like soft cheese.* The 

 yellow colour reappears on adding a few more drops of 

 nitric acid. The acid acts in this instance as the oxygen of 

 the atmosphere at a temperature from 27 to 35 ; for the 

 white coagulum grows yellow in two or three minutes, when 

 exposed to the sun. After a few hours the yellow colour 

 turns to brown, no doubt because the carbon is set more 

 free progressively as the hydrogen, with which it was com- 

 bined, is burnt. The coagulum formed by the acid becomes 

 viscous, and acquires that smell of wax which I have 

 observed in treating muscular flesh and mushrooms (morels) 

 with nitric acid. According to the fine experiments of Mr. 

 Hatchett, the albumen may be supposed to pass partly to 

 the state of gelatine. The coagulum of the papaw-tree, 

 when newly prepared, being thrown into water, softens, dis- 

 solves in part, and gives a yellowish tint to the fluid. The 

 milk, placed in contact with water only, forms also mem- 

 branes. In an instant a tremulous jelly is precipitated, 

 resembling starch. This phenomenon is particularly striking 

 if the water employed be heated to 40 or 60. The jelly 

 condenses in proportion as more water is poured upon it. 

 It preserves a long time its whiteness, only growing yellow 

 by the contact of a few drops of nitric acid. Guided by the 

 experiments of Fourcroy and Vauquelin on the juice of the 



* The substance which falls down in grumous and filamentous clots is 

 not pure caoutchouc, but perhaps a mixture of this substance with caseum 

 and albumen. Acids precipitate the caoutchouc from the milky juice of 

 the euphorbiums, fig-trees, and hevea; they precipitate the caseum from 

 the milk of animals. A white coagulum was formed hi phials closely 

 stopped, containing the milk of the hevea, and preserved among our col- 

 lections, during our journey to the Orinoco. It is perhaps the develop- 

 ment of a vegetable acid which then furnishes oxygen to the albumen. 

 Th6 formation of the coagulum of the hevea, or of real caoutchouc, is 

 nevertheless much more rapid in contact with the air. The absorption of 

 atmospheric oxygen is not in the least necessary to the production of 

 butter which exists already formed in the milk of animals ; but I believe 

 it cannot be doubted that, in the milk of plants, this absorption produces 

 the pellicles of caoutchouc, of coagulated albumen, and of caseum, which 

 we successively formed in vessels exposed to the open air. 



