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This mode of experimenting however is inapplicable on the 

 prefent occafion, the different fpecies of mineral coal being not 

 fo readily inflammable as to carry on the combuftion in this 

 manner. Hence I contented myfelf v/ith the common manner, 

 only ufing fuch precautions as to render its refults tolerably uni- 

 form, and repeating each experiment feveral times. 



I EXAMINED the purity of the nitre I employed by nitrated 

 filver, and found by the quantity of falited filver produced that 

 480 grains of the nitre contained 3,5 grains of common fait, 

 135 grains of muriated filver indicating 100 of common fait; 

 hence the conftant quantity of nitre I ufed was 483 5 grains, ex- 

 cept in the experiments on bitumens, as I had not enough of them 

 to expend on fo large a quantity of nitre. 



The nitre was heated barely to rednefs before anv coal was 

 projeded on it in a wind furnace and a very large crucible ; upon 

 this uniform degree of heat much of the uniformiiy of different 

 experiments on the fame fpecies of coal depends. 



In my firft experiments the coals were reduced to a very fine 

 powder, and then projeded on the ignited nitre, but I obferved 

 that by this method much more of each fpecies of coal was .'e- 

 quifite to alkalize the ftandard quantity of nitre than when it 

 was reduced to a coarfe powder, about the fize of a pin's head or 

 fomewhat larger, and the reafon is, that by the force of the ex- 

 plofion much of the finer powder is carried off without having 



been 



