upon Gun-powder, &e. 527 
I was willing to fee the effect of mixing fait of tartar with gun- 
powder, and accordingly having provided fome of this alkaline 
fait in its pureff ftate, thoroughly dry, and in a fine powder, I 
fnixed 20 grains of it with 145 grains of gun-powder; and 
upon difcharging a bullet with the mixture, I found that tire 
alkaline fait had confiderably leffened the force of the powder. 
See experiment N° 78. 
I next made ufe of fal ammonidcum . That, fait has been 
found to produce a very large quantity of elaftic air, or vapour, 
when expofed to heat under certain circumffarices ; but when 
20 grains of it were mixed with a charge of gun- powder, in- 
{bead of adding to its force, it diminifhed it very feniibly. See 
the 80th experiment. 
Moff, if not all, the metals, are thought to produce large 
quantities of air when they are diffolved in proper menjlrua, and 
particularly brafs, when it is diflblved in fpirit of nitre. Be- 
ffrous of feeing if this could be done by the flame, or acid 
vapour of fired powder, I mixed 20 grains of brafs in a very 
fine, powder, commonly called brafs duff (being the ffnall 
particles of this metal that fly off from the wheel in fharpening 
ffns), with 145 grains of powder, and with this compound 
*nd a fit bullet I loaded my barrel and difeharged it ; but the 
experiment (N° 8 1 .) fhewed, that the force of the powder was 
not increafed by the addition of the brafs duff, but the con- 
i trary. 
It feems probable*, however, that neither brafs duff nor 
anhiops mineral are of themfelves capable of diminifhing the 
force of gun- powder in any conffderable degree, otherwife thaw, 
oy filling Up the interff ices between the grains, and obftrudting 
the paffage of the flame, and fo impeding the progrefs of the in- 
ff immation. And hence it appears, how earthy particles and 
X x 2 impurities 
