MECHANICS AST) USEFUL ARTS. 121 



ure by coal diminishes in proportion to the teruperatxire employed in 

 its carbonization, but its power of conducting heat grows with the 

 higher degree of temperature employed ; the power of conducting elec- 

 tricity is also much increased by a higher temperature, and the electric 

 light is more brilliant. In proportion as the density of coal increases, the 

 facility of burning decreases. Coal obtained at a low degree of heat is 

 more inflammable than that carbonized at a higher degree. While coal 

 obtained at a low degree of heat burns at 340 deg., coal for ammunition 

 powder requires 370 deg. ; coal made at 1,000 and 1,200 deg. bums only 

 upon tin heated to cherry-red heat. Sulphur burns only at 250 deg., but 

 it occasions the deflagration of saltpetre at 432 deg., while coal produces it 

 at 380 deg. Thus in burning your powder it is the sulphur which first 

 takes fire ; it ignites the coal, which in its turn communicates fire to the 

 saltpetre. 



It is to be remembered that carbonization referred to by M. Yiolette 

 was effected in closed retorts, by means of dry heated steam. The tem- 

 peratures referred to are the centigrade. 



The improvements in the manufacture of powder, introduced at Es- 

 querdes, in France, under the direction of M. Yiolette, and which have 

 given to the products of this manufactory a reputation exceeding that of 

 any other, depend on a new method of preparing the charcoal, which is 

 obtained by calcination of the wood by means of a current of overheated 

 steam. This charcoal, called carbon roux, has but one objection its price. 

 To overcome this difficulty, M. Gossart has devised a method of executing 

 this process by heating with gas, which saves about 80 per cent, of the cost 

 of the process for heating the steam. 



It is apparent that this method is not only applicable to steam and to 

 carbonization, but maybe employed with advantage whenever a fluid is to 

 be heated. But the author has had in view specially the making of red 

 charcoal, (carbon roux,~) and on this point it has been examined by the 

 Committee of the Ordnance Department of France. The following is an 

 extract from the report of this Committee to the Minister of War : 



"With the apparatus proposed 100 kilogrammes of wood may be car- 

 bonized at once. The following is the method : The water for evaporation 

 is injected through a pump whose piston is charged with a weight little 

 above the force of tension desired for the vapor. The pressure causes the 

 water to rise through a graduated orifice, in a series of tubes arranged, like 

 a ladder, and enclosed in tubes of larger bore. These last convey the gas, 

 and also serve for the condensation of the steam after it leaves the carbon- 

 izing apparatus. The circulation goes on from above downwards. By 

 this arrangement the cold water of the tubes will absorb the greater part of 

 the heat of the gas and of the condensed water, thus heating itself more 

 and more in its upward movement ; it finally reaches the temperature of 

 ebullition, and is in part turned into steam, in a serpentine with parallel 

 tubes arranged so as to cover the top and sides of the furnace. The water 

 vaporizes in these tubes, and is overheated in its passage across the metal 

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