140 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1&17. 



a layer of vaseline or paraffin. If the interior of the cartridge is 

 firmly partitioned off by resistant diaphragms, these will also tend 

 to protect the charge from the friction due to its inertia to rotation. 

 The use of a simple cartridge in metal or cardboard appears to be 

 advisable in all cases, but particularly for base-loading shells of large 

 capacity. 



It is possible to build up the charge by the aid of several separate 

 cartridges and by this means avoid the difficulties encountered in 

 seeking to obtain, through fusion, a long column of perfectly homo- 

 geneous explosive. In all cases this rids one of the serious incon- 

 venience which results from the fused explosive running into the 

 space between the projectile and its base plug. It also prevents dust 

 from the explosive getting into the threads of the plug or into the 

 fuse device. 



If the explosive be formed by mixing a solid and a liquid, these 

 will be found evidently the best conditions from the point of view of 

 safety, since under these circumstances abnormal heating of an 

 isolated point will be much less likely to occur and all friction of 

 solid on solid will be avoided. But, on the other hand, another in- 

 convenience presents itself, viz, e/, the acceleration of translation to 

 which the charge is subjected at the instant the projectile starts on 

 its travel of the bore. It follows as a result of this acceleration that 

 the difference between the apparent specific gravities of the solid and 

 liquid components of the explosive is multiplied by /. There is then 

 shown a tendency of the explosive to separate into its two compo- 

 nents, following the axis of the projectile, at the moment of departure 

 from the gun. In order for such an explosive to be acceptable it is 

 necessary that the difference in the specific gravities of its compo- 

 nents shall be as small as possible. 



One may theoretically consider the uses of liquid explosives such 

 as Sprengel's (dinitrobenzene and nitric acid, F=99-i9) or one of 

 the panclastites of Turpin (nitrobenzene and hyponitrous acid; 

 F=-10,860; naphthalene and hyponitrous acid; 7^=11,700). In this 

 case the question of safety on departure appears completely assured ; 

 but the intimate mixing of the components of the mixture will not 

 be effected unless they are miscible. 



2. PRINCIPAL EXPLOSIVES UTILIZED. 



As a rule, up to the present, only those solid explosives composed 

 of nitrated derivatives of the aromatic series have been used as charges 

 for artillery projectiles.^ It is expedient now to study the properties 



^ The Austrian artillery appears to have tentatively used the mixture of ammonium 

 nitrate and alumiuum known as ammonal, but the sensitiveness to percussion and fric- 

 tion of explosives having an Al base appears to have led to its discontinuance. 



