USE OF EXPLOSIVES AND THE BLOW-LAMP IN THE GARDEN. 9 



One piece of my ground had recently been double-dug before the 

 exploding, and it was obvious that much of the force was wasted. 



Just as with digging, exploding should not be done when the 

 soil is soppy and waterlogged ; frost does not matter much provided 

 a safe, i.e. frost-proof, explosive is used. For good work it is essential 

 that no air-space should be left around or below the cartridge ; now 

 the end of the hole is a mould of the pointed end of the bar, and 

 unless this is filled, the explosion is liable to cause the formation of 

 a cavity under the surface, and so loss of power which should have 

 been applied to the solid ground. Consequently, before the cartridge 

 is lowered into place, the pointed end of the hole should be filled 

 with fine, dry, sifted earth. In the later explosions in my garden, 

 I filled the ends of the holes with ground lime, and put some also 

 above the cartridge, with the secondary intention of breaking up 

 the clayey subsoil more permanently. This lime lies very close, and 

 makes an excellent bed for the cartridges, but whether it becomes 

 sufficiently disseminated to be of real use I do not know.* 



The cartridge having been lowered into place, more fine soil is 

 poured in, and gently rammed down with the stemming stick ; there- 

 after the rest of the hole is filled with earth and well rammed down 

 after each addition. The end of the fuse, which should have been cut 

 so that about an inch or two projects above the ground level, may 

 again be freshened if the weather is moist, and then lighted, most 

 conveniently by an ordinary fusee. It may be noted that the 

 explosions are by no means spectacular or noisy, and that no pieces 

 of earth should be projected into the air. It is probably advantageous 

 to explode a number of holes simultaneously, but this is hardly 

 practicable unless high-speed fuse or electric ignition is used. 



After the results of this trial shot have been noted, the work may 

 be continued. It is preferable to plan out the sites of the holes, and 

 have them made in advance, so that there may be no waiting. Should 

 they become v/aterlogged, the junction of cartridge case and fuse 

 must be coated with grease. 



We now come to the consideration of the size of the charges, and 

 the distances of the holes apart. This is closely related to the 

 question of cost, the object being to get the optimum effect with the 

 least expenditure ; it is further tempered by the nature of the subsoil. 

 I am given to understand that with the explosive " cheddite " a 

 4 oz. cartridge of if in. diameter, which is fired at a depth of 3 feet 

 and 10 feet from the next, gives a loosening effect in clay soil to a 

 depth of 4 J feet, and affects a circle of radius about 5 feet ( =8| square 

 yards). In the soil of a garden which has a good tilth for about 18 

 inches, the loose character of the upper layers will no doubt lead to 

 a smaller working effect. 



* It would be interesting to determine how far such substances are driven 

 into the soil, as could easily be done by using a lithium or strontium compound, 

 and examining portions taken with a sampling tool at different distances by 

 means of the spectroscope. 



