[ I50 ] 



hours did not lofe their luftre until almoft r% of them had dif- 

 appeared, and at laft left reddifh afhes amounting to 7,13 grains, 

 nearly 2,7 per cent. Projedling this coal in fine powder on 480 

 grains of pure ignited nitre, I found the fait required 65 grains of 

 the coal to alkalize it, but only 50 grains when in coarfe pow- 

 der ; and in a third experiment, when the crucible was farther 

 from the flue of the furnace, only 49 grains : fo that I look upon 

 50 grains as being in round numbers neareft to the truth. That 

 is the proportion of one part of Kilkenny coal to 9.6 of nitre, or 

 100 parts of nitre require for their decompofition 10,416 of Kil- 

 kenny coal. 



This proportion of coal is much fmaller than that of charcoal 

 in Mr. Lavoifier's experiment, which we have feen to be as i to 

 7,57, or as 13,21 to 100, which I attribute to the advantageous 

 mode in which his experiment was inftituted, as already ex- 

 plained ; whereas in mine and the ufual way, the decompofition 

 of nitre is promoted by the external heat applied, as well as by 

 the coal, and confequently lefs of coal is employed. 



From the experiments of Scheele one might be led to infer 

 that the proportions of charcoal and nitre neceflTary to the alkali- 

 zation of this latter approach ftill nearer to each other than in 

 Lavoifier's ftatement, and confequently much nearer than in mine; 

 for in his efi^ay on plombago he tells us that five parts nitre are 

 Jufficient to confume one of charcoal, and confequently it fiiould 

 feem that one part charcoal ftiould decompofe no more than five 



of 



