MANUFACTURE BY DISSOLVING. 159 



preparation of tin plate or other metals for the manufacturer of 

 those materials. Although the gum becomes, after being 

 crushed, apparently as hard and unyielding as ever, it is, never- 

 theless, permanently prepared and subdued by the separation of 

 the particles, for spreading, whenever it is warmed up. For 

 these reasons it might be kept prepared and sold like other raw 

 materials. 



MANUFACTURE BY DISSOLVING. 



This method is, at the present time, so far superseded by that 

 of crushing and spreading^^with callenders heated by steam, as 

 before described, that it is hardly considered worthy of notice ; 

 it will, however, be found that it has its own peculiar merit for 

 particular purposes, for the manufacture of tissue, fine drapery, 

 and gum-elastic sponge, and for cement it is indispensable ; so 

 that instead of going into disuse, it will be very extensively used 

 in the manufacture of gum-elastic. 



The gum is dissolved most readily by being first chopped fine, 

 and being placed in iron or metal vessels, or vats, and adding 

 camphene or turpentine enough to cover it, requiring usually 

 about one quart to the pound of gum ; this will bring the gum to 

 the consistence of a very stiflf paste when ground or kneaded ; it 

 is afterwards reduced, by adding camphene, to any desired con- 

 sistency. In order to render it liquid enough to be used with 

 the brush for cement, or to be spread with the knife, represented 

 by machine No. 5, about a gallon of camphene is required. 



Whenever it is desired to bring the gum to a liquid state, 

 without the aid of machinery, it should first be chopped fine, and 

 put into from three to four quarts of the solvent to a pound of 

 gum, and stirred once in an hour or two, until it becomes dis- 

 solved. 



It was the neglect to cut the gum in pieces small enough, and 

 to add enough of the solvent at one time, that caused the art of 



