S2 Prof. Christison's Analysis of' the Vegetable Milk 



softer ; and at 212° its consistence is soft enough to allow it to 

 flow, like very thick mucilage. A greater heat adds little to its 

 fluidity, but produces brisk effervescence, during which acid 

 vapours are discharged, and the whole mass becomes translucent 

 and yellowish, like a resin. When allowed to cool after this 

 change has taken place, it retains its translucency, and for some 

 days is soft and extremely viscid ; but at length it acquires the 

 consistence and firmness of bees-wax. A still higher tempera- 

 ture applied to it in a tube, causes the usual decomposition 

 which vegetable substances in general undergo, and a large 

 quantity of pyro-acetic acid is formed. When a light is applied 

 to it, it catches fire, and burns entirely away, with a large white 

 flame, and much black smoke. 



Water, cold or boiling, has no action on this substance. It 

 merely fuses and rises to the surface of the water. Alcohol acts 

 slightly on it, and only with the aid of heat : a small portion is 

 dissolved by boiling alcohol, and the greater part separates in 

 the form of a white cloud, when the spirit cools. Sulphuric 

 ether acts on it with rapidity, dissolving the greater part of it, 

 and leaving about four per cent, of a soft viscid mass. 



It is unnecessary to mention any of the other chemical pro- 

 perties of the compound substance, as they are almost entirely 

 the same with those I shall presently relate, as characterizing that 

 part of it which is soluble in ether. 



The portion insoluble in ether, when left exposed to the air 

 for some hours till the adhering ether had evaporated, became a 

 greyish, viscid, elastic, ductile substance, which, when heated to 

 212", so as to remove the whole ether, and then left for some 

 days exposed to the air, lost its viscidity, became brownish 

 black, and acquired the external appearance and all tlie chemi- 

 cal and physical properties of caoutchouc. It is ductile and 

 elastic, insoluble in water, alcohol, or caustic potass ; is merely 

 softened and swelled up in sulphuric ether ; is easily dissolved 

 by oil of turpentine ; has a density of 934 ; undergoes imper- 

 fect fusion at a temperature above 212°, and does not after that 

 recover its solidity on cooling ; and when held to the flame of a 

 candle, it takes fire and burns with a bright white flame, and 

 much smoke. 



The portion of the concrete juice which is dissolved by the 



