222 TESTIKa CHARCOAL. 



process, it is best to ascertain the quantity of the charcoal by 

 measure. This is usually and most conveniently done with baskets 

 of known capacity. If the weight also is required, it is easy enough 

 to weigh a few basketfuls and strike a mean for the weight of one 

 basketful. 



Section V. — Testing Chaecoal. 



Charcoal may be described in general terms as a black, more or 

 less lustrous and porous, but fairly compact, substance, of low speci- 

 fic gravity, and possessing neither smell nor taste. These properties 

 are subject to some slight modifications according to the wood 

 from which it is made. We have already seen that the specific 

 weight is, for all practical purposes, directly proportional to the 

 density of the wood ; the heavier the wood is, the heavier will be 

 the charcoal. We know, too, that the weight of charcoal also 

 depends on the dryness of the wood and the slowness of the car- 

 bonisation. 



Good charcoal is black with a steel-blue metallic lustre, and has 

 a conchoidal fracture. If the kiln has been kept burning too long, 

 that is to say, if the wood has been allowed to burn on for some 

 time after it has become carbonised, the charcoal assumes a deep 

 black colour, and loses its characteristic lustre ; it also becomes 

 porous and lighter. On the other hand, if the carbonisation is 

 incomplete, the charcoal is of a foxy-red colour, and emits a heavy 

 smoke in burning. Good charcoal gives out a clear metallic ring 

 when struck or when thrown together or stirred about ; whereas 

 over burnt charcoal returns a very dull clink and insufficiently burnt 

 charcoal a deader sound even than wood. Both good charcoal and 

 overburnt charcoal burn without smoke ; but the latter emits no 

 flame at all, takes fire almost instantaneously, and is very quickly 

 consumed. 



Charcoal possesses great power of absorbing gases ; from moist 

 air it will take up watery vapour sufficient to increase its weight 

 from 8 to 12 per cent. It also absorbs water with avidity, taking 

 up from 25 to 30 per cent, of its own weight in a few minutes, and 

 from 60 to 120 per cent, in the course of only 8 hours. Hence 

 the sale of charcoal by weight leaves much room for fraud and 

 should never be employed. 



