240 Dr THOMSON'S Experiments on the 



white colour, and the opacity and consistence of wax. It is not 

 brittle like bees-wax, but plastic, at least when the temperature 

 is not lower than 60, which was the heat of my laboratory when 

 I was engaged in examining the properties of gallactin. 



Like wax, it becomes a transparent liquid when exposed to 

 heat. This liquid has many of the characters of a fixed oil, ren- 

 dering paper transparent, and burning with great brilliancy when 

 kindled by means of a wick. As the change from solidity to a 

 state of liquidity takes place gradually, it is not easy to assign 

 the true melting point of gallactin. At 117 it was solid, at 137 

 it was fluid. Between 117 and 137 it passes through an infi- 

 nite number of different degrees of softness, before it becomes as 

 liquid as possible. When we heat the white flocks which are 

 deposited from alcohol, they emit abundance of aqueous vapour, 

 and the gallactin does not become a transparent liquid till kept 

 for some time in the temperature of 170, showing that these 

 white flocks consist of water and gallactin united together. 



Gallactin is as tasteless as wax ; but when put into the mouth 

 it becomes soft and plastic, and adheres strongly to the teeth, 

 having no bad resemblance, in point of consistency, to the gluten 

 of wheat, when just freed from the starch. But the colour of 

 this plastic gallactin is snow-white. 



When gallactin is heated on a platinum or silver spoon, it 

 melts, and then frothes strongly. When the frothing is at an 

 end, the colour has become brownish-yellow. On increasing the 

 heat to 640, the gallactin begins to boil, and the vapour catch- 

 ing fire, burns with a bright yellow flame, giving out smoke, and 

 ultimately disappears, leaving behind a minute quantity of white 

 ashes. 



This white residue has no action on vegetable blues, showing 

 that it contains neither a fixed alkali nor lime. It dissolved in 

 nitric acid, with the exception of a very minute portion, which 

 was probably silica, though its quantity was too minute to admit 



