[ H5 ] 



The firft ftep towards carrying this analytic plan into execu- 

 tion muft therefore be to determine the quantity of pure carbon 

 neceflary to decompofe a given quantity of pure nitre. But 

 here many pradical difficulties occur which fliall prcfcntly be 

 mentioned ; the moft perfed method of obviating them was that 

 employed by the ever memorable Lavoifier : He mixed the pureft 

 nitre with charcoal alfo purged of the inflammable as well as 

 other airs and water which it ufually abforbs, in the proportion 

 which, after feveral trials, he found requifite for the entire dc- 

 compofition of that fait, rammed them into a copper tube, fired 

 them, and continued the inflammation under water, by which 

 means the charcoal was aded on folely by the air educed from 

 the nitre, to the intire exclufion of the external air, and this air 

 was educed, folely by the Ignited charcoal, to the entire exclufion 

 of external heat, advantages that cannot be procured by the 

 ufual mode of effeding this decompofition ; thus he found the 

 proportion of charcoal necefl^ary for the entire decompofition of 

 nitre to be as i to 7,57, or in other words, that 13,21 parts char- 

 coal decompofe 100 of nitre*, and yet even in this experiment I 

 find a fmall inaccuracy, as he did not take the water employed 

 in mixing the nitre and charcoal into the account, and hence, and 

 for fome other reafons, the detail of which would lead me too 

 far, I think the proportion fliould be as i to 7,868 nearly, or 

 that 12,709 charcoal decompofe 100 of nitre; but the difference 

 is of little importance. 



Vol. VI. T This 



• 1 1 Mem. Scav. Etrang. p. 626. 



