rui: farm holding. 



139 



and destroy the logs like the more rapid gelignite and dynamite do. . Black 

 powder is exploded by lire and not by detonation, and tlio ordinary safety 

 fuse is used for this purpose. 



Safety fuse is the ordinary powder fuse, used for firing blasting powder, 

 and attached to a detonator for firing gelignite, dynamite and rack-a-rock. 

 It consists of a continuous core of powder through the centre of an inflam- 

 mable and practically waterproofed wrapper, is made with great skill and 

 very little variation, and is tested carefully by the Explosives Department, 

 having to answer certain rigid requirements before it is permitted to be 

 placed on sale. The rate of burning is about 2 feet per minute, and 

 for land-clearing purposes., where charges are usually fired shortly after they 

 are tamped, it is quite waterproof. There are several makes on the market, 

 the double tape being pre-eminently the best, but of unnecessarily high 

 quality and price for land-clearing purposes, where a cheaper article, such as 

 " blue sump," is quite as effective. 



Fig. 4. — Crimping the cap on the fuse. 



All the foregoing explosives have their adherents, and justly so, but 

 gelignite is recommended as the safest in the hands of the farmer, who 

 is not necessarily an explosive specialist. Gelignite is all ready prepared 

 in convenient cartridge or plug form, will stand a considerable amount of 

 rough handling, is not affected by water, and can probably be purchased 

 more generally than any of the other explosives. It is somewhat too 

 suddenly strong and rapid in its effect, however, and appears to give 

 better service when slowed down mechanically. In very cold weather 

 gelignite, in common with all nitro-glycerine compounds, becomes frozen, 

 getting as hard as a board. In this condition it should not be used, on 

 account of its liability to miss-fire and, curious though it may appear, of 

 its greater sensitiveness to friction. Its susceptibility to explosion in this 

 frozen condition is due, experts tell us, to the rubbing together of the frozen 

 ice crystals of nitro-glycerine. Proper warming pans are on the market 

 for the purpose of thawing out frozen gelignite, but a simple and effective 



