392 CHEMICAL DISCOVERY AND INVENTION 



whether originating from gas or dust, the explosives to be used 

 in fiery or dusty mines have to pass a Government test. A 

 testing gallery has been erected by the Home Office at Rother- 

 ham, and there the effects of various explosives on an explosive 

 mixture of gas and air are carried out. A charge is fired from a 

 gun with a 2-inch bore, which represents a bore-hole, into the 

 cylinder containing an explosive mixture of gas and air, or air 

 in the presence of coal-dust laid along the cylinder. Shots are 

 then fired electrically till the largest charge is found, which can 

 be fired without igniting the mixture. Further shots are then 

 fired till five shots of the same weight have been fired without 

 igniting the mixture. 



Strictly speaking there is no such thing as a perfectly safe 

 explosive ; under certain unfavourable conditions they will all 

 ignite gas or coal-dust, but the " permitted test " does enable 

 the various explosives to be sorted into grades of safety, and 

 only those which have shown themselves to be the safest are 

 allowed to be used (Macnab). 



In consequence of the extensive manufacture and use of ex- 

 plosives in modern times it has been necessary, in all civilised 

 countries, to regulate by legislation the conditions under which 

 they may be made, stored, and distributed. Many of the enact- 

 ments are self-evident in their application : buildings for the 

 factory must be licensed, stores in mines and quarries must be 

 registered, explosives must be properly packed, and imports from 

 abroad require special licences. Inspectors are also appointed 

 whose business it is to make surprise visits for the purpose of 

 observing that the regulations for the safety of workpeople and 

 all the conditions of the licences are duly carried out. 



Explosives of any new composition require to pass a strict 

 examination before they are authorised, and all must be in a 

 condition which indicates reasonable safety when kept and 

 freedom from serious danger from friction or blows when packed 

 or in transit. 



Explosives differ considerably in stability, some being liable 

 to slow decomposition which in course of time may assume a 

 dangerous character. This is especially true of the nitric "esters," 

 that is so-called nitrocelluloses and nitroglycerin, and more 

 especially if the temperature is somewhat elevated as in tropical 

 countries, in the holds of ships, and especially in positions where 

 the temperature may be raised in consequence of the position of 



