POWDER. 89 



them well, lest any particle of cinder should adhere 

 to theni) keep constantly shifting the powder from 

 the one to the other, without allowing it to remain 

 sufficiently long on either, to cool the plate. The 

 powder will then be more effectually aired, and more 

 expeditiously dried, than by the more common means 

 of using one plate, which the powder, by lying on 

 it, soon makes cold, and therefore the plate requires 

 to be two or three times heated. (This is another 

 little discovery since the earlier editions). Nothing 

 preserves the strength of powder better than, after 

 being dried, to put it into canisters, securely corked 

 from the air. Mr. Butts latterly did so, by my ad- 

 vice. Beware of going any where near the fire to 

 dry powder on plates. Recollect how far a hot 

 cinder will sometimes fly, and therefore, to be on the 

 sure side, run with your hot plates out of the room, 

 and go where there is no fire. As a still safer plan 

 too, I might name the use of a common pewter 

 water plate ) or dish ; by having recourse to which 

 there can be no risk of accident ; except that, through 

 awkwardness, the powder might be wetted, instead of 

 being dried. This way of drying is much on the same 

 principle as that which is now in general use in 

 powder works; -r/s. by means of steam passing through 

 pipes, or other receptacles, by transfusion of heat 

 through those pipes, or cases, from which the air of 

 the drying room is heated to as great a degree as is 

 requisite for the purpose of drying the powder. 

 Good powder burns red hi the pan, will keep its 



