VARIETIES OF DYNAMITES. 433 



Dynamite with Hasting powder as base. 



Dynamite with saltpetre and charcoal as base. 



Dynamite having as base barium nitrate and resin, or charcoal, 

 with or without the addition of sulphur. 



Dynamites having as base sodium nitrate, charcoal, and sulphur, 

 etc. 



Dynamites formed by nitroglycerin, saltpetre and wood saw- 

 dust, or starch, or cellulose. 



9. (2nd) Dynamites having as base pyroxyl, such as Trauzl 

 dynamite, formed of nitroglycerin and gun-cotton in a paste. 



Abel's glyoxylin, formed of the same substances, with the 

 addition of saltpetre. 



Dynamites having as base a nitrified ligneous substance (paper 

 pulp, or wood pulp), and analogous ones. 



Blasting gelatin, formed by the association of 93 to 95 parts 

 of nitroglycerin, and 5 to 7 parts of collodion cotton. 



10. We should here note that the relative proportions of 

 nitroglycerin and of the combustible or explosive base, which 

 are the most useful in practice, are not always those which 

 correspond to a total combustion ; either because an incomplete 

 combustion gives rise to a greater volume of gas, or because the 

 rapidity of decomposition and the law of expansion vary accord- 

 ing to the relative proportions and the conditions of application. 



11. It can further be seen that the inert, the simple com- 

 bustible, and the explosive combustible substances may be 

 associated in various proportions, and this constitutes fresh 

 dynamites with mixed base, extremely varied. 



The requirements of practice and the imagination of inventors 

 are daily multiplying these varieties, designated by the most 

 diversified and sometimes the most pompous names : Hercules 

 powder, giant powder) petralites, etc. ; but they all belong to the 

 five foregoing types. 



12. Among these practical requirements we shall point out 

 some of those which play the most important part, inde- 

 pendently of the question of the first cost. The most important 

 point lies in the strength of the mixture. Indeed, the additions 

 have generally the effect of lowering the strength, by reducing 

 the amount of nitroglycerin. It is sought in this way to retard 

 decomposition, so as to change the shattering agent into a 

 propulsive agent. But if the retardation be too great, we enter 

 into the category of the slow powders (p. 2), and lose the 

 advantages due to the presence of nitroglycerin. There is, 

 therefore, a practical limit to these additions, if it be desired to 

 obtain the greatest useful effect. The use of mica, on the 

 contrary, increases the rapidity of explosion. 



The homogeneousness and stability of the mixture are of the 

 highest importance ; it is, in fact, requisite that the nitroglycerin 

 should be entirely absorbed by the substance which serves as 



2F 



