Two chief varieties of the new brown powders are now made, and are known as 'slow-burning cocoa'--from the fact that cocoa-nut fibres were first employed in the experiments--and 'Prism brown I.' The former contains about four per cent. of sulphur, and burns rather more rapidly than the latter, which contains only two per cent. Baked straw is the material now used to supplant the charcoal, as it provides a form of cellulose which may be readily reduced to a fine state of division. The shape is still the perforated hexagonal prism introduced in America. The burning of these powders is steady and the increase of pressure gradual, attaining a maximum when the bullet is about half-way down the barrel of the gun. The damage inflicted on the firing-chamber is very slight; perhaps as slight as ever will be obtained with such large charges of powder. Uniformity of velocity is secured by ensuring that in the making the proportions employed shall be accurate and the mixing complete. The prisms of any given class of powder are made exactly the same in weight and composition, and in consequence, a charge composed of a given number of prisms will give in every case almost exactly the same propelling force. It is thus that fine aiming adjustments are made possible, as two consecutive bullets of the same weight may be propelled almost exactly the same distance--varying only a few yards in a range of several miles--by equal weights of powder of uniform composition. But explosives of the present day are composed of other substances. Cordite, of which we now hear so much, is made of nitro-glycerine, gun-cotton, and mineral jelly in the proportion of fifty-seven, thirty-eight, and five parts. It is also steeped in a preparation of acetone. Gun-cotton itself is dipped in a mixture of three parts of sulphuric to one of nitric acid. The force of cordite over gunpowder may be judged from the following facts. A cartridge containing seventy grains of black powder fired in the ordinary rifle of the army will give what is called a muzzle velocity of one thousand three hundred and fifty feet a second, while thirty grains only of cordite will give a velocity of two thousand feet. In larger arms, a little less than a pound of cordite fired in a twelve-pounder gun will give more velocity than four pounds of black powder fired in the same weapon. It need hardly be said that in the experiments at Shoeburyness it is the new-fashioned explosive which is chiefly used.