The density of the powder is then calculated by the following formula :— Density = (Pi D x 100 — P) ± 100 where D is the specific gravity of the mercury at the time of experiment, P the weight of globe full of powder and mercury, PI the weight of globe full of mercury alone, and 100 the weight of powder employed.
explosive is formed by the action of ooncentrated nitric acid on cotton, and has the composition indicated by the formula A number of similar products are known, but only one is used as an explosive agent. Some of the others are largely used for making collodion.
The operation of cleansing the cotton waste is effected by boiling it in a solution of carbonate of soda. After the soda has been thoroughly removed by washing in water, the cotton is completely dried by means of heat, and the passage of expanding air between the fibres.
The cleansed and perfectly dried fibre is then treated with acid. The acid used for the purpose is a mixture of one part of highly concentrated nitrio acid, with three parts of concen trated sulphuric acid. Much heat is evolved in the operation of mixing the two acids. The mixture must be allowed to cool before using it. Suitable quantities of acid liquor are placed in stone jars, kept cool by immersion in water, and into these jars dried cotton is gradually introduced, in the proportion of 1 lb. of fibre to 15 lb. of acid, and left to soak for a period of 48 hours. By the action of the acid a chemical change in the composition of the cotton is effected, the elements of the acid liquor, in the form of peroxide of nitrogen, being substituted by chemical process for a portion of the hydrogen of the cotton fibre, and the fibre is thereby converted into a highly explosive compound termed guncotton. The chemical action does not destroy the texture of the cotton.
After the uncombined acid liquor has been removed from the fibre as far as practicable by means of a centrifugal drying machine of the usual description, the acidulated cotton fibre is thrown in small quantities at a time into a cascade of cold water, and is well washed to free the fibre from every trace of uncombined or free acid.
A certain amount of care must be exercised during the process of immersing the fibre in the acid, as well as in the operation of sousing the acidulated material in the cascade of water. There is not the slightest danger of explosion in these portions of the operation, but without care and attention be bestowed, portions of the material are liable to be destroyed, with violent escapes of ruddy fumes produced by rapid chemical action.
One hundred parts by weight of cleansed and dry cotton fibre, furnish about one hundred and seventy-five parts of pure guncotton fibre, weighed in a dry state. The acidulated fibre, or as it may now bo correctly termed, the guncotton, is afterwards submitted for a considerable period of time to the action of a pulping machine, such as is ordinarily in use in paper mills. When tho cotton fibres have been reduced to pulp of a proper consistency and degree of fineness, and every trace of free acid therein has been neutralized, the pulp is collected on strainers and conveyed to the granu lating machine, or to the hydraulic presses, in case the pulp is to bo formed into compressed charges or discs in place of being granulated. It is sent out either wet or dry. In the former ease it should contain 10 per cont. of moisture, and will require redrying for use unless exploded by a dry primer of guncotton, or an excessively strong denotator such as a sextuple.
Cotton powder or Tonite.—The guncotton used in the manufacture of cotton powder is crushed to a flour meal consistency ; this is next purified by being subjected in large vats to strong agitation by an air blast, while it is brought to a boiling point by a jet of steam, and a dose of carbonate of ammonia is thrown in the vat ; all the unstable nitrogen compounds are destroyed at that temperature, and the nitrous fumes so difficult of extraction by the old process are, by the aid of ammonia, reduced into their simple elements, nitrogen and water ; the water in the vat from a colourless state has now become dark brown. This operation takes three hours, and the guncotton is then quite safe for dry storage ; of course it is subsequently separated from the dirty water until quite clean. Nitrate of baryta hes some properties which render it especially suited for nitrating guncotton, namely it is scarcely soluble in cold water, so when the charge dries it does not separate and distort the shape of the cartridge; it also contains the largest amount of oxygen under the same volume. So that with the fineness of the guncotton and the density of the baryta, the charges of the cotton powder can be made to density 1.500; which it is claimed produces 'intense local action. The safety of cotton powder against blows or similar causes of explosion is illustrated by the fact, that whereas dynamite is usually exploded with seven grains of fulminate of mercury, it takes fully fifteen grains to ensure the explosion of cotton powder.