CHARCOAL 



763 



vapours freely escape, especially towards the end of tho operation, for -when they are 

 re-absorbed, they greatly impair the combustibility of the charcoal. 



By the common process of the forests, about 18 per cent, of the weight of tho wood 

 is obtained ; by the process of Foucauld about 24 per cent, is obtained, with 20 of crude 

 pyroligneous acid of 10 Baume". By the process described under ACETIC Aero, 27 of 

 charcoal, 18 of acid at 6, are procured from 100 parts of wood, besides the tar. These 

 quantities were the results of careful experimenting, and are greater than can be 

 reckoned upon in ordinary hands. 



Charcoal for chemical purposes may be extemporaneously prepared by calcining 

 pieces of wood covered with sand in a crucible, till no more volatile matter exhales. 



The charcoal of some woods contains silica, and is therefore used for polishing 

 metals. Being a bad conductor of heat, charcoal is employed sometimes in powder to 

 encase small furnaces and steam-pipes. It is not affected by water ; and hence, the 

 extremities of stakes driven into moist ground are not liable to decomposition. In 

 like manner casks when charred inside preserve water much better than common casks, 

 because they furnish no soluble matter for fermentation or for food to animalcules. 



Lowitz discovered that wood charcoal removes offensive smells from animal and 

 vegetable substances, and counteracts their putrefaction. He found the odour of suc- 

 cinic and benzoic acids, of bugs, of empyreumatic oils, of infusions of valerian, essence 

 of wormwood, spirits distilled from bad grain, and sulphureous substances were all 

 absorbable by freshly-calcined charcoal properly applied. A very ingenious filter has 

 been constructed for purifying water, by passing it through strata of charcoal of 

 different degrees of fineness. 



When charcoal is burned, one-third of the heat is discharged by radiation, and two- 

 thirds by conduction. 



The following Table of the quantity of charcoal yielded by different woods was pub- 

 lished by Mr. Mushet, as the result of experiments carefully made upon the small 

 scale. He says, the woods before being charred were thoroughly dried, and pieces of 

 each kind were selected as nearly alike in every respect as possible. One hundred 

 parts of each sort were taken, and they produced as under : 



Lignum Vitae afforded 



Mahogany 



Laburnum 



Chestnut 



Oak 



Walnut . 



Holly . 



Beech 



Sycamore 



Elm 



Norway Pine 



Sallow . 



Ash 



Birch 



Scotch Pine 



26-0 of charcoal of a greyish colour, resembling coke. 



25 '4 tinged with brown, spongy and porous. 



24*5 velvet black, compact, very hard. 



23-2 glossy black, compact, firm. 



22-6 black, close, very firm. 



20-6 dull black, close, firm. 



19-9 dull black, loose and bulky, 



19-9 dull black, spongy, firm. 



19-7 fine black, bulky, moderately firm. 



19*5 fine black, moderately firm. 



19 '2 shining black, bulky, very soft. 



18 -4 velvet black, bulky, loose and soft. 



17-9 shining black, spongy, firm. 



17*4 velvet black, bulky, firm. 



16*4 tinged with brown, moderately firm. 



Messrs. Allen and Pepys, from 100 parts of the following woods, obtained the quan- 

 tities of charcoal as under : 



Beech 

 Mahogany . 

 Lignum Vitae 



. 15-00 

 . 15-75 

 . 17-25 



Oak 

 Fir 

 Box 



. 17-40 

 . 18-17 

 . 20-25 



It is observable that the quantities obcained by Messrs. Allen and Pepys are in 

 general less than those given by Mr. Mushet, which may be owing to Mr. Mushet not 

 having applied sufficient heat, or operated, long enough, to dissipate all the aqueous 

 matter of the gaseous products. 



To those persons who buy charcoal by weight, it is important to purchase it as soon 

 after it is made as possible, as it quickly absorbs a considerable portion of water from 

 the atmosphere. Different woods, however, differ in this respect. Messrs. Allen and 

 Pepys found that by a week's exposure to the air, the charcoal of 



Lignum Vitas gained . 



Fir . 



Box .... 



Beech 



Oak . 



Mahogany 18-0 



9-6 per cent. 

 13-0 

 14-0 

 16-3 

 16-5 



