';_' ON THE HEAT EVOLVED 



before the wood could be charred. The whole of the woods, 

 which had been previously filed into oblong solids, presenting 

 sharp edges, to detect any loss by fracture, each being designated 

 by notation letters, made by incision, were thus surrounded and 

 exposed in the first instance to a moderate heat in an air fur- 

 nace, which was increased to a white heat, and so remained for 

 about two hours, during which time additional quantities of 

 powdered coal were introduced through the aperture at the 

 top of the inverted crucible. 



The product of charcoal from the several woods obtained 

 in this manner, will be found in the table. 



Among the many experiments made to discover the best 

 manner of ascertaining the weight of charcoal product from 

 the different woods, and to satisfy myself whether any loss 

 could take place in a solid piece of coal surrounded by pow- 

 dered charcoal, a piece of box wood coal without fissures was 

 taken, weighing 23.7 grains, and after having been exposed to 

 a white heat for three hours, was found to weigh 23.1 grains; 

 the loss of T % of a grain, was, however, undoubtedly, produced 

 by the air contained in the piece of coal, or conjointly with 

 that in the interstices between the powdered coal, contiguous 

 to the piece when first ignited. 



A similar experiment was made in clean dry white sand, 

 upon a piece of maple coal without fissures, which had been 

 previously exposed in powdered charcoal to a white heat, ana 

 known to be perfectly charred and dry. This piece of coal 

 weighed 26 grains, and lost by the process 6 grains ; the surface 

 was found entirely changed from its original hard texture, 

 having become soft, and the colour was changed from slate to 

 jet black, which is often found to be the case in charcoal ob- 

 tained in the large way, and is always objectionable, as it pro- 

 duces loss both to the collier and consumer. 



The charcoal produced by surrounding the wood with pow- 

 dered coal was found of a slate colour on its surface, dense, 

 sonorous, brittle and equal in all respects to that made in 

 cylinders or retorts for gunpowder, which is known to be much 

 superior to that produced by the ordinary method, even fov 



