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pile of wood logs with some channels for air, covering- it with a 

 layer of turf and setting it on fire. Combustion begins, but 

 the supply of air is purposely made too small to allow it to proceed 

 far. The wood gives off various gases and other volatile sub- 

 stances under the influence of the heat and a residue of charcoal 

 remains. This is nearly pure carbon, but it still contains a little 

 hydrogen and the mineral matters which, if the wood had been 

 completely burnt, would have been left behind as ash. The con- 

 struction of the pile varies in different places. The wood may be 

 placed vertically or, as in Sweden, Horizontally, and the fire may 

 be applied at the top or at the bottom. I do not know whether 

 charcoal-burning is still carried on in this country in the old- 

 fashioned way, it certainly survived until quite lately. A far 

 more economical way of making charcoal is by heating wood in 

 retorts somewhat after the fashion of those in which coal is heated 

 for gas-making. The volatile substances given off are collected 

 and from them acetic acid, naphtha and creosote are prepared. The 

 yield of charcoal is about 25 per cent, of the weight of wood used. 

 Charcoal is used as a domestic fuel in many countries and in the 

 extraction of metals from their ores. The very best iron, for 

 example, is that made from magnetite with charcoal as fuel; both 

 it and the ore being free from the sulphur which is so objectionable 

 an impurity in the metal. Charcoal is also used in the conver- 

 sion of iron into steel by the cementation process. Bars of iron 

 are imbedded in charcoal and the whole heated until the iron has 

 taken up the required proportion of carbon. The lower parts of 

 gate posts, telegraph poles, and the like are often charred so as 

 to convert the outer layers of the wood into charcoal and thus 

 preserve it from decay. According to an article in the " Satur- 

 day Magazine" for January 2nd, 1836, charcoal, bemg imperish- 

 able, has been used as "an enduring landmark, although a truly 

 inconspicuous one, the custom being to bury it beneath the soil 

 on the boundary." Wood charcoal has a great capacity for 

 absorbing gases and is used as a disinfectant and deodorizer, thus 

 it is often put at the ventilating openings of sewers and the like. 

 A similar service is performed by the lump of charcoal put into a 

 hyacinth-jar, or, mixed with fibre, into flower pots. Charcoal is 

 used for filtering, domestic charcoal-filters, for use in country 

 places with a water supply of doubtful purity, were at one time 

 very common. In the chemical laboratory blocks of charcoal' are 

 much used and charcoal is as familiar and useful to the artist as 

 to the student of science. In medicine it is used both for in- 

 ternal administration and externally as a poultice. Alone or with 

 other ingredients it makes an excellent tooth-powder. Some 

 dyspeptics think highly of charcoal biscuits, but it cannot be 

 reckoned as a food. I have left to the last perhaps the most im- 

 portant of the uses of wood charcoal, the manufacture of gun- 

 powder. This contains somewhere about 15 per cent, of charcoal, 

 10 per cent, of sulphur, and 75 per cent, of nitre, although the 

 proportions vary. By heating bones in iron retorts, bone black, 



