Lieut. Willoughby Walke, of the U.S. Artillery, has recently communicated to the journal of the American Chemical Society an important paper on the relative strengths of modern high explosives, which is interesting as illustrating the considerable variation in the comparative strengths, not only of different explosives of acknowledged value, but of the same explosive manufactured at different times and under slightly different conditions. C. E. Munroe has already pointed out that the firing point of an explosive is also a very variable number. In his more recent experiments, a thin copper cartridge was placed in a molten 5 bath of tin or paraffin, the initial temperature noted by a thermometer, and the bath quickly heated until the explosive flashed off, when the temperature marked by the thermometer was. again noted. The following table shows some of the results obtained: - -

Description of Explosives.

Firing Point in deg. C.

Compressed military guncotton ......

186-201

Air-dried military gun-cotton

179-186

,, ,, ,,

186-189

,, ,, ,,

137-139

,, ,, ,,

154-161

Gun-cotton dried at 65° C. .

136-141

Air-dried collodion gun-cotton

186-191

,, ,, ,,

197-199

,, ,, ,,

193-195

„ gun-cotton

192-197

,, ,, ,,

194-197

Hydronitro cellulose

201-213

Nitro-glycerine..

203-205

Kieselguhr dynamite, No. 1 .

197-200

Explosive gelatine..

203-209

„ „ camphorated

174-182

Mercury fulminate

175-181

Gunpowder..

278-287

Hill's picric powder

273-283

,, ,, ,,

273-290

Forcite ,No.1..

184-200

Atlas powder, 75 per cent. .

175-185

Emmensite,No1..

167-184

,, No.2..

165-177

,, No.3..

205-217

Lieut. Willoughby Walke, in his experiments, employed a Quinan pressure gauge for registering the pressures developed by the explosives, in preference to other methods used by the older investigators, as even the crusher used by Berthelot gave only approximate results, as shown by Sarau and Vieille. The instrument employed consisted of a heavy block of wood bolted to a cast-iron base, in which were 4 iron guides set around a 4-in. circle. A steel plate is let into the iron block flush with its upper surface, and a ring holds the guides in place at the top. The piston is a cylinder of tempered steel moving freely between the guides, and rests on a plug of lead which is to be compressed.