Chemical Preparations. 291 
Isend you a few canisters of percussion powder, from chlorate of 
potash. It is, in my opinion, preferable to all other kinds of compo- 
sition for igniting gun powder. It is used, one grain at a time, for 
priming, except the No. 2, which is used in magazine locks. The 
No. 8 is used here for firing cannon. The red is coated, to make it 
water proof. It is perfectly safe in use, projecting no fragments of 
copper, as is done with the caps, whilst it is one hundred times more 
certain to discharge a gun, and costs ninety per cent. less. 
From an expression in your Chemistry,* I suspect you doubt the 
possibility of using fulminating mercury as a certain means of firing 
guns loaded with common gun powder. Fulminating mercury alone 
used for that purpose is useless, because the heat does not continue 
a sufficient time to ignite the powder ; not, that it is not hot enough, 
for, if it be ground with some material that retains heat some little 
time, it makes one of the most certain primings that can be used. I 
instituted a great number of experiments to ascertain this fact; and 
likewise what substance would best answer the purpose, and finally 
selected oxide of tin. Three parts of fulminating mercury and one 
part of oxide of tin, ground together with a stiff solution of starch, 
sive a powder of which I have manufactured a great deal, and so far 
as I know, it has scarcely ever, if at all, missed firing the piece in which 
it was used. Starch was the only thing that I could find that would 
give cohesiveness to the grain without injuring its explosive qualities 
Under percussion ; and it was a curious fact that solutions of shellac 
in aleohol should be harmless in powder from chlorate of potash, and 
Tuin that from fulminating mercury 3 whilst starch was harmless in 
fulminating mercury, and spoiled powder from chlorate of potash. 
‘send you a little of this kind of priming, under the name of metal- 
lie Priming, in two canisters. It is not very handsome, but as we 
“onstruct our own gun locks, I suspect there is not a grain amongst 
It that will not set a gun off with the celerity of lightning. 
2. Purirication oF o1L oF TURPENTINE. 
Few things that have engaged my attention, have cost me so much 
rouble as divesting spirits, or rather oil of turpentine, of the last par- 
ticle ofits resin. If you have given the sample I sent you a compar- 
ave trial with common oil of turpentine, you will perceive that 
I have accomplished my object, whether or not to any good 
* Vol. IL. pa. 33. par. at bottom. 
