1818.] M. Humboldt on Vegetable Milk. 115 



is soluble in half its weight of water ; with the boracic acid it 

 forms a very deliquescent compound. In general, the action of 

 borax and the different borates upon the supertartrate of soda 

 is very similar to that upon the cream of tartar. 



We have some observations on the formation of the soluble 

 cream of tartar by M. Meyrac ; he gives the following process. 

 One hundred grains of supertartrate of potash and 400 grains of 

 water are first boiled together, 124- grains of vitrified boracic 

 acid are then added and boiled for some minutes, the supertar- 

 trate is dissolved, most of the tartrate of lime is precipitated, the 

 fluid is filtered when cold, the liquor evaporated to dryness, and 

 the salt which is obtained reduced to fine powder. An addition 

 of -i- part of boracic acid is necessary ; if less be added, the cream 

 of tartar loses much of its solubility, and the solution can only 

 be effected by protracting the ebullition. If the solution of the 

 Soluble cream of tartar be exposed for some days under a 

 receiver enclosing lime, crystals may be procured, but they are 

 too small for their form to be perceptible. 



Article VII. 



On the Milk of the Cow Tree, and on vegetable Milk in General, 



By M. Humboldt* 



M. Humboldt and his companions, in the course of their 

 travels, heard an account of a tree which grows in the vallevs of 

 Aragua, the juice of which is a nourishing milk, and which, from 

 that circumstance, has received the name of the cow tree. As 

 the milky juices of plants are in general acrid, bitter, and even 

 poisonous, M. Humboldt was at first scarcely disposed to credit 

 the account, but experience proved it to be correct. 



The tree in its general aspect resembles the chrysophyllum 

 cainito ; its leaves are oblong, pointed, leathery, and alternate, 

 marked with lateral veins, projecting downwards, they are 

 parallel, and are ten inches long. M. Humboldt had no oppor- 

 tunity of seeing the flower ; the fruit is somewhat fleshy, and 

 contains one or sometimes two nuts. When incisions are made 

 into the trunk, it discharges abundantly a glutinous milk, mode- 

 rately thick, without any acridness, and exhaling an agreeable 

 balsamic odour. The travellers drank considerable quantities of 

 it without experiencing any injurious effects ; its viscidity only 

 rendering it rather unpleasant. The superintendent of the plant- 

 ation assured them that the negroes acquire flesh during the 



" Abridged from an essay in Ann. dp Chim. for Feb. 1818, which is ao extract 

 from a memoir read to the Academy of Sciences. 



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