The mixing itself is generally performed in a separate house.  In a series of lead-lined tanks the guhr is weighed, placed in a tank, and the nitro-glycerine poured on to it.  The nitro-glycerine may be weighed out in indiarubber buckets.  The whole is then mixed by hand, and well rubbed between the hands, and afterwards passed through a sieve.  At this stage the dynamite should be dry and powdery, and of a uniform colour.

It is now ready to be made up into cartridges, and should be taken over to the cartridge huts.  These are small buildings surrounded with mounds, and contain a single cartridge machine.  Each hut requires three girls—­one to work the press, and two to wrap up the cartridges.  The cartridge press consists of a short cylinder of the diameter of the cartridge that it is intended to make.  Into this cylinder a piston, pointed with ivory or lignum vitae wood, works up and down from a spring worked by a lever.  Round the upper edge of the cylinder is fastened a canvas bag, into which the powdery dynamite is placed by means of a wooden scoop, and the descending piston forces the dynamite down the cylinder and out of the open end, where the compressed dynamite can be broken off at convenient lengths.  The whole machine should be made of gun-metal, and should be upright against the wall of the building.  The two girls, who sit at tables placed on each side of the press, wrap the cartridges in parchment paper.  From these huts the cartridges are collected by boys every ten minutes or a quarter of an hour, and taken to the packing room, where they are packed in 5-lb. cardboard boxes, which are then further packed in deal boxes lined with indiarubber, and fastened down air tight.  The wooden lids are then nailed down with brass or zinc nails, and a label pasted on the outside giving the weight and description of the contents.  The boxes should then be removed to the magazines.  It is well to take a certain number of cartridges from the packing house at different times during the day, say three or four samples, and to test them by the heat test.  A sample cut from a cartridge, about 1 inch long, should be placed under a glass shade, together with water (a large desiccator, in fact), and left for some days.  A good dynamite should not, under these conditions, show any signs of exudation, even after weeks.[A]

[Footnote A:  For analysis of dynamite, see chapter on “Analysis,” and author’s article in Chem.  News, 23rd September 1892.]

Properties of Kieselguhr Dynamite.—­One cubic foot of dynamite weighs 76 lbs. 4 oz.  The specific gravity of 75 per cent. dynamite is, however, 1.50.  It is a red or grey colour, and rather greasy to the touch.  It is much less sensitive to shock than nitro-glycerine, but explodes occasionally with the shock of a rifle bullet, or when struck.  The addition of a few per cent. of camphor will considerably diminish its explosive qualities to such an extent that it can be made non-explosive except to a very