436 DYNAMITES. 



3. Dynamite proper results, as we have said, from the 

 association of nitroglycerin with amorphous silica. At the 

 outset Nobel employed for this purpose Kieselguhr, that is, 

 the silicious earth of Oberlohe (Hanover) ; but there have since 

 been found in various places natural silicas, such as randanite 

 (Auvergne), which answer the same purpose. 



The special structure and the organic origin of these varieties 

 of silica, formed for the greater part of shells and infusoria 

 (Diatoms), were at first regarded as indispensable for the 

 fabrication of dynamite. But amorphous silica, prepared by 

 a chemical process for instance, that resulting from the action 

 of water on silicon fluoride is no less suited for this preparation ; 

 it even stores up at least as large quantities of nitroglycerin 

 (more than nine times its weight) as natural silica. 



4. Dynamites are also distinguished according to their origin 

 as Nobel and Iboz dynamites, Vonges dynamites, etc. ; and 

 according to their strength No, 1 dynamite, with 75 per cent. 

 of nitroglycerin ; No. 2 dynamite, with 50 per cent. ; No. 3 

 dynamite, with 30 per cent. 



5. Preparation. The silica is first dried in ovens, without 

 however heating it to too high a temperature, and sifted to 

 eliminate the large grains 5 then the nitroglycerin is incorporated 

 with it. A few hundredth parts of lime or magnesia carbonates 

 or of sodium bicarbonate are added in order to prevent the 

 mixture from becoming acid, a transformation which is the 

 prelude to its spontaneous decomposition. 



6. Properties. The substance thus obtained is grey, brown, 

 or reddish (according to the foreign ingredients), rather greasy 

 to the touch, forming a pasty mass. It should not give rise to 

 considerable exudations of nitroglycerin; The absolute density 

 of dynamite is a little more than 1 - 60. The relative density, 

 obtained by the gravimetric method, is 1'50 for dynamite at 75 

 per cent. 



In preparing dynamite an apparent contraction of the 

 materials is observed; that is to say, that the nitroglycerin 

 occupies a volume less than the air interposed in the silica. 

 Nitroglycerin freezing at 12, dynamite is transformed at about 

 this temperature, or slightly below, into a hard mass, expanding 

 at the same time. The properties of dynamite are then 

 extremely modified, and it requires much stronger detonators 

 to explode it ; say 1'5 grm. of fulminate, instead of 0'5. How- 

 ever, the explosive force remains the same. This circumstance 

 forms one of the most serious drawbacks to the keeping and 

 use of dynamite. Indeed the necessity for thawing it frequently 

 occasions serious accidents, especially if this operation be 

 effected at an open fire and without precautions. It was in 

 this way that at Parma, in 1878, a lieutenant of cavalry having 

 placed on a brazier a can containing one kgm. of dynamite, an 



