380 GENERAL DATA. 



for a long time on a sand-bath, as the nitroglycerin gradually 

 evaporates and the substance consequently loses part of its power. 

 The elevation of the temperature might also give rise to the 

 rapid vaporisation of certain components and consequently to 

 their elimination, for instance in the case of compounds con- 

 taining nitric peroxide, which boils at 26. 



4. The state of preservation should remain satisfactory even 

 in very varied hygrometric conditions of the surrounding 

 atmosphere. 



It is this condition which has led to deliquescent bodies such 

 as sodium nitrate being excluded from the manufacture of 

 service powder. This salt should also be avoided in the manu- 

 facture of dynamite, seeing that the accidental formation of a 

 concentrated solution of sodium nitrate due to the deliquescence 

 of the solid salt determines the separation of the existing 

 nitroglycerin and transforms this substance into a non-homo- 

 geneous and very dangerous mixture. 



Diazobenzene nitrate becomes completely decomposed under 

 the influence of moisture. 



5. The salts with which sea air is impregnated constitute a 

 special cause of change which must be borne in mind, especially 

 as regards explosives which are to be employed on board ships, 

 or even conveyed by them, since the air eventually penetrates 

 into the best closed vessel, owing to the variations of tempera- 

 ture and pressure. 



6. From this point of view it is useful to know whether an 

 explosive substance resists the action of liquid water, which may 

 accidentally moisten explosive substances, especially at sea. 

 It is well known that water destroys service powder by dis- 

 solving the saltpetre : by a kind of liquefaction it gradually 

 displaces the nitroglycerin in silicious dynamite. 



Dynamites which contain nitrates are also decomposed by 

 water. 



Silicious dynamite deposited in running water gradually 

 loses its nitroglycerin by way of solution, since nitroglycerin is 

 slightly soluble in water. 



On the other hand, pure water does not affect gun-cotton 

 whether the latter be simply moistened or plunged into running 

 water. The inflammability of the substance, which is checked 

 by the presence of water, reappears completely after drying. 



Moistened gun-cotton can moreover be kept and even 

 employed in that state with less danger of accidental ignition 

 than in the dry state. 



However, gun-cotton which is kept moistened for a long time 

 may become the seat of mould and other microscopic plants 

 which alter the properties in the long run. 



7. The slow exudation of the nitroglycerin in dynamites 

 made with bad materials forms an obstacle to their preservation, 



