Chemical Preparations. 291 



I send 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 Httle 

 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, 

 gave 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 alcohol should be harmless in powder from chlorate of potash, and 

 ruin that from fulminating mercury ; whilst starch was harmless in 

 fulminating mercury, and spoiled powder from chlorate of potash. 

 I send you a little of this kind of priming, under the name of metal- 

 lic-priming, in two canisters. It is not very handsome, but as we 

 construct 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. Purification of oil of Turpentine. 



Few things that have engaged my attention, have cost me so much 

 trouble as divesting spirits, or rather oil of turpentine, of the last par- 

 ticle of its resin. If you have given the sample I sent you a compar- 

 ative trial with common oil of turpentine, you will perceive that 

 I have accomplished my object, whether or not to any good 



Vol. H. pa. 33. par, at bottom. 



