138 THE farmers' handbook. 



Gelignite and dynamite are both nitro-glycerine compounds, and for land 

 clearing purposes they practically do the same work, but there is a vast 

 difference in their character and method of manufacture, which stands out 

 in favour of one to the exclusion of the other, for the farmer who is not 

 necessarily an expert with explosives. 



Dynamite is a mechanical mixture and soluble in water, that is to say, 

 the nitro-glycerine.. being only absorbed or taken up in a containing earth, 

 separates out from that containing oarth on coming in contact with water, 

 and this crude form of nitro-glycerine is highly sensitive to friction, even 

 when a wooden tamping stick is in use. It is highly dangerous for the 

 reason that the farmer may frequently be working in wet ground when 

 clearing, and the above conditions would operate. Many serious fatalities 

 have been attributed to this solubility of dynamite. 



Gelignite is a definite chemical compound, being nitro-glycerine gelatinised 

 chemically and mixed with certain other ingredients. It is quite insoluble in 

 water, and if left in it for long periods would certainlv deteriorate, but its 

 chemically combined parts would never separate. 



Both of these explosives — dynamite and gelignite — will burn freely if a 

 match is applied, and in the open air in such a condition would be com- 

 paratively harmless ; but if thrown into a hot confined fire, where air had 

 very little access, such as a stove fire, or a fierce burning log, serious results 

 are likely, for the reason that as the explosive burns, the gases produced by 

 the chemical change are generated very rapidly, and not being able to get 

 away they form a pressure about themselves, which explodes them — really 

 spontaneous combustion. 



Rack-a-rock is a combination of two chemicals, one a solid and the other a 

 liquid, neither being classed as an explosive separately but becoming so 

 when they are brought together as rack-a-rock. The solid section consists 

 of a 98 per cent, chlorate of potash cartridge, packed in small calico bags of 

 sausage shape and varying diameter. The liquid is an oil known generally 

 as murbane or almond oil, and chemically as nitrate of benzole, and by 

 soaking the chlorate of potash cartridge in the murbane oil for about three 

 minutes, it becomes a powerful explosive. It is somewhat slower in its 

 explosive action than nitro-glycerine compounds, as used in this State, and 

 for that reason it is well adapted to the work of land clearing; but it is of 

 very little use in wet holes or wet ground, not for the same reason as dynamite 

 but because water apparently breaks up the chemical combination of the 

 chlorate of potash and the murbane oil, rendering it inoperative. All the 

 foregoing — gelignite, dynamite, and rack-a-rock — are exploded by detonation 

 through a No. 6 detonator, and not through the ordinary fuse by itself, 

 though it is good practice to use half a plug of gelignite in addition, as a 

 primer, when firing rack-a-rockj as a No. 6 detonator often proves not to 

 be strong enough for absolute certainty. 



Black powder is a proportional mechanical mixture of three substances — 

 nitre, sulphur and charcoal — not so strong in explosive force as any of the 

 foregoing, and very much slower in its action. Its slow pushing action is 

 ideal for work in the soils, but the lack of explosive force throws black powder 

 out when handling trees and stumps ; it is used extensively for log splitting 

 in the sleeper-cutting and timber business, as its slow action does not shatter 



