764 



CHARCOAL 



The following is a tabular view of the volumes of the different gases which wore 

 absorbed in the course of 24 hours, by one volume of charcoal, in the experiments of 

 M. Theodore de Saussure, which were conducted in a way likely to produce correct 

 results. Each portion of charcoal was heated afresh to a red heat, and allowed to 

 cool under mercury. When taken from the mercury, it was instantly plunged into the 

 vessel of gas : 



Ammoniacal gas 

 Muriatic acid gas 

 Sulphurous acid 

 Sulphuretted hydrogen 

 Nitrous oxide 

 Carbonic acid gas 



90 Bicarburetted hydrogen 35'00 



85 Carbonic oxide . . 9'42 



65 Oxygen gas . . . 9'25 



65 Nitrogen . . . 7-50 



40 Carburetted hydrogen . 5'00 



35 Hydrogen gas . . T75 



Neumann, who made many experiments on charcoal, informs us that for tho reduc- 

 tion of the metallic oxides, the charcoal of the heavier woods, as that of the oak and 

 the beech, is preferable, and that, for common fuel, such charcoal gives tho greatest 

 heat, and requires the most plentiful supply of air to keep it burning ; while those of 

 the lighter woods preserve a glowing heat with a much less draught of air ; and that 

 for purposes where it is desirable to have a steady and a still fire, charcoal should be 

 employed which has been made from wood previously divested of its bark, since it is 

 the cortical part which crackles and flies off in sparks during combustion, which the 

 coal or the wood itself seldom does. 



For making crayons of charcoal, the willow is the best wood that can be employed, 

 as the softness is uniform in all its parts. The durability of charcoal may be seen in 

 several of our old churchyards, where the letters made with lampblack are still per- 

 fect, though the white lead with which the body of the stones was painted is entirely 

 destroyed. 



This property of carbon is shown, however, in a more striking manner by the 

 writings that were found in the ruins of Herculaneum, which have retained their 

 original blackness for two thousand years. The ancients wrote with ink made from 

 ground charcoal. 



If it be required to purify any carbonaceous matter, to render it fitter for delicate 

 pigments, this may be done by first calcining it in a close vessel, and then lixiviating 

 it in water slightly acidulated by nitric acid. 



The incorruptibility of charcoal was well known to the ancients, and they availed 

 themselves of this property upon all important occasions. 



About sixty years ago a quantity of oak stakes were found in the bed of the Thames, 

 in tho very spot where Tacitus says that the Britons fixed a vast number of such 

 stakes, to prevent the passage of Julius Caesar and his army. These stakes were 

 charred to a considerable depth, h'ad retained their form completely, and were firm 

 at the heart. 



Most of the houses in Venice stand upon piles of wood, which have all been pre- 

 viously charred for their preservation. In this country, estates were formerly marked 

 out by charred stakes driven to a considerable depth into the ground. These are 

 occasionally found, and usually the charred portions are quite perfect, although every 

 other part has decayed. 



ANIMAL CHABCOAL. Animal charcoal especially, and other charcoal occasionally, 

 has been much employed in the construction of filters for domestic use. The ad- 

 vantage of charcoal as a purifying agent through which to pass water has been 

 long established. But it cannot be too generally known that the charcoal, in a few 

 weeks loses the property upon which its value depends. When first used, it separates 

 not only the matters mechanically suspended in water, but much of the organic 

 matter and salts held in solution. The property, appears to be entirely lost in about 

 two months, after which time it is necessary either to renew or to restore tho charcoal. 

 See FILTER and BONE BLACK. 



LIGNITE CHABCOAL. Much of the lignite or brown coal of the Continent has been 

 converted into charcoal, with a view to its use in metallurgical works. Mayer 

 says that very firm charcoal is obtained by charring freshly-dug lignite with- 

 out previously exposing it to the air. The complaint, however, amongst metallur- 

 gists is, that it is not generally sufficiently coherent for the furnace. The following 

 are a few of the results of practical experiments : 



Lignite from Cologne, produced per cent, of charcoal . 36*1 



Iceland 

 Friesdorf 



Stosschen 



Paredel 



Oberpfalz 



57-5 

 48-2 

 40-6 

 42'0 

 46-0 



