79 
The solution of albumen does not coagulate when 
it contains much less than 1000 parts of albumen ; 
but it appears that gluten requires more than 1000 
parts of cold water for its solution. 
Gluten when burnt affords similar products to 
albumen, and probably differs very little from it in 
composition. Gluten is found in a great number 
of plants : Proust discovered it in acorns, chesnuts, 
horse-chesnuts, apples, and quinces; barley, rye, 
peas, and beans ; likewise in the leaves of rue, 
cabbage, cresses, hemlock, borage, saffron, in the 
berries of the elder, and in the grape. Gluten 
appears to be one of the most nutritive of the ve- 
getable substances ; and wheat seems to owe its 
superiority to other grain, from the circumstance 
of its containing it in larger quantities. 
(j. Gum elastic , or Caoutchouc , is procured from 
the juice of a tree which grows in the Brazils, 
called Haevea. When the tree is punctured, a 
milky juice exudes from it, which gradually de- 
posits a solid substance, and this is gum elastic. 
Gum elastic is pliable and soft like leather, and 
becomes softer when heated. In its pure state it 
is white ; its specific gravity is 9 335. It is com- 
bustible, and burns with a white flame, throwing 
off a dense smoke, with a very disagreeable smell. 
It is insoluble in water, and in alcohol ; it is solu- 
ble in ether, volatile oils, and in petroleum, and 
may be procured from ether in an unaltered state, 
by evaporating its solution in that liquid. Gum 
elastic seems to exist in a great variety of plants : 
amongst them are, Jatropha elastica , Ficus indie a > 
Artocarpus integrifolia , and Urceola elastica , 
