In the manufacture of picric acid the first obvious and most necessary precaution is to isolate the substance from other chemicals with which it might accidentally come into contact. If pure materials only are used, the manufacture presents no danger. The finished material, however, must be carefully kept from contact with nitrates, chlorates, or oxides. If only a little bit of lime or plaster become accidentally mixed with it, it may become highly dangerous. A local explosion may occur which might have the effect of causing the explosion of the whole mass. Picric acid can be fired by a detonator, 5-grain fulminate, and M. Turpin patented the use of picric acid, unmixed with any other substance, in 1885. The detonation of a small quantity of dry picric acid is sufficient to detonate a much larger quantity containing as much as 17 per cent. of water. It is chiefly due to French chemists (and to Dr Sprengel) that picric acid has come to the front as an explosive. Melinite,[A] a substance used by the French Government for filling shells, was due to M. Turpin, and is supposed to be little else than fused picric acid mixed with gun-cotton dissolved in some solvent (acetone or ether-alcohol). Sir F.A. Abel has also proposed to use picric acid, mixed with nitrate of potash (3 parts) and picrate of ammonia (2 parts) as a filling for shells. This substance requires a violent blow and strong confinement to explode it. I am not aware, however, that it has ever been officially adopted in this country. Messrs Designolles and Brugere have introduced military powders, consisting of mixtures of potassium and ammonium picrates with nitrate of potassium. M. Designolles introduced three kinds of picrate powders, composed as follows:-- ___________________________________________________________________ | | | | | | | For Torpedoes | For Guns. | For Small | | | and Shells. | Ordinary. Heavy. | Arms. | |___________________|_______________|___________________|___________| | | | | | | | Picrate of Potash | 55-50 | 16.4- 9.6 | 9 | 28.6-22.9 | | Saltpetre | 45-50 | 74.4-79.7 | 80 | 65.0-69.4 | | Charcoal | ... | 9.2-10.7 | 11 | 6.4- 7.7 | |___________________|_______________|___________|_______|___________|