132 GUN-COTTON. —Manufacture of Collodion.

cotton, and immunity from explosion -when' merelylighted or ignited, the committee appointed by Mr.Cardwell in 1871 for the purpose of consideringand reporting upon the general question of themanufacture, storage, and use of gun-cotton, affirmedthat their experiments “ conclusively proved thatgun-cotton, in the ordinary damp state in which itis stored, and to the extent of 1 ton, will even underthe most trying conditions of confinement bumaway without explosion when once ignition hasbeen established.”

The force developed by the explosion of gun-cotton is much greater than that obtained from anequal weight of gunpowder. If they be comparedwhen acting in a closed chamber, the eruptive powerof the cotton will be found to be nearly five timesthat of the powder. In an unconfined space thedifference becomes still greater; the incisive effectobtained by the detonation of gun-cotton, as des-cribed, being more than ten times that of an equalweight of gunpowder. It is therefore evident thatmuch saving will accrue to the miner by the use ofthe former instead of the latter. His shot holesmay be drilled of only one-half the usual diameter,and yet be able to do the same work.

When duly rammed home, granulated gun-cottonassumes a density equal to about 50 lbs. per cubicfoot, or (M63 oz. per cubic inch. The approximateweight of wet granulated gun-cotton that a shothole of a given diameter and depth will contain,when properly charged, may be calculated from thefollowing formulae:—

•00035 D 2 X L = W. lb.

•0056 D 2 X L = W. oz.,

in which D = diameter of hole in terms of eighthsof inches; L = length or depth of explosive (whenrammed) in terms of inches; W lb. — weight ofgranulated wet explosive in pounds; W. oz. = weightof granulated wet explosive in ounces.

For dry gun-cotton the constants are respec-tively :—

•00028 for the weight.in pounds,

•00448 for the weight ill ounces,

and for gunpowder weighing 62 lbs. per cubic foot,or 0'574 ozs. per cubic inch—

•0004375 for the weight in pounds,

•007 for the weight in ounces.

Thus a shot chamber 1£ inch, or ten-eighths ofan inch in diameter, by 5’9375, or 5|-f inches indepth, will contain of wet granulated gun-cotton(10 2 X 5-9375 X -0056 = 3-325) say 3£ ozs.

It will have been noticed that there is a consider-able percentage of carbonic oxide in the gases pro-duced by the explosion of gun-cotton. The wellknown poisonous nature of this gas being considered,it is easy to see that in driving headings in tunnelsand mines, and in sinking shafts, a certain amountof time must bo lost after each explosion in waitingfor this gas to diffuse itself. In order to do awaywith this inconvenience, nitrated gun-cotton issometimes used. This is produced by incorporating

ordinary pulp with saltpetre or nitrate of soda in theproportion of 40 parts by weight of one of thesesalts to each quantity of pulp capable of producing100 parts of gun-cotton, weighed in the dry state.When these nitrated compounds are exploded, theproducts of combustion furnish but little, if any,carbonic oxide. They are harder, less liable toflake, and less inflammable, without being less efficientthan ordinary gun-cotton.

It is sometimes necessary to dry small quantitiesof gun-cotton. This is accomplished in the open air,the apparatus consisting of a tray or drawer fitted witha false bottom, made of perforated sheet copper, uponwhich the charges rest during the operation of dry-ing. Over the tray is a shallow reservoir for steam,and this again is covered by a sheet of iron in acurved form, to protect the upper surface from thecooling effects of currents of air and showers of rain.The gun-cotton is thus dried by radiant heat; andas the temperature of the steam is not allowed to riseabove 215° Fahr. (a pressure of 1 lb. per squareinch above that of the atmosphere), no difficulty isexperienced or danger incurred in the operation.

Collodion. —It has already been stated that theproduct of the action of sulphuric and nitric acidson cellulose varies with the proportion of waterpresent. We have hitherto been dealing with gun-cotton properly so called—namely, that produced bythe strongest acids. The other compounds, althoughnot adapted for use as explosives, have found severaluseful applications. Their value depends mainly ontheir solubility in a mixture of ether and alcohol; thecollodion of the photographer, the most importantof them, being obtained from pyroxylin by dissolvingit in this menstruum. The following formulae forthe production of this soluble pyroxylin are takenfrom IIardwicke’s “ Manual of Photography : ”—

(1.) Strong sulphuric acid,. 6 fluid ozs.

Dried nitre. 3| ozs. (avoir.).

Water,. 1 fluid oz.

Best bleached and dried cotton wool, 60 grains.

(2.) Sulphuric acid, spec. grav. 1-845,... 18 fluid ozs.

Nitric acid, spec. grav. 1-457. 6 “

Water,. 5^ “

Dried cotton wool,. 300 grains.

Other formulas are given, and in all processesseveral precautions are necessary to insure a goodyield of soluble pyroxylin.

The acids and water, or the acid, nitre, and water,are mixed first. A considerable amount of heat isdeveloped in this process; and as it is necessary thatthe conversion should be conducted at a temperaturenear 140° Fahr., the mixture is allowed to cool downto that point before proceeding. If the temperaturebecome lower, the vessel containing the mixture isfloated on warm water till the operation is completed,in order that the acids may be at the right tempera-ture throughout. The cotton, in tufts about thesize of a walnut, is thrown into the acids, allowed toremain there a short time, and then quickly washedin a large excess of water. The pyroxylin obtainedis dissolved in a mixture of ether and alcohol, theproportions of these employed depending on the