CARBON AND CARBONIC ANHYDRIDE. 79 



the chamber, which are lined with leather. There are two 

 objects in having the cone one to prevent the smoke from 

 passing upward too rapidly, and the other to present a 

 large surface for the deposition of the powder in addition 

 to that of the walls of the chamber. 



93. Bone-Black. Bone or ivory black is a powdered char- 

 coal prepared from bones. It is far from being pure char- 

 coal, as you will see as we explain its preparation. A bone 

 is composed of two parts mingled together, a mineral and 

 an animal part. These can be obtained separate from each 

 other, as has been fully shown in the " First Book of Physi- 

 ology." It is the animal part alone that really furnishes 

 charcoal ; but in the preparation of bone-black both parts 

 are used together. The bones are heated in iron vessels, 

 and the heat, driving off all the volatile ingredients of the 

 animal part, leaves the carbon mingled with the mineral 

 portion the phosphate of lime. The advantage of this form 

 of charcoal is that the carbon is very minutely divided by 

 being thus mingled with the mineral powder. Besides other 

 uses soon to be noticed, bone-black is used in the manufact- 

 ure of blacking, being mixed for this purpose with oil of 

 vitriol and sirup. 



94. The Carbon in Animal Substances. As there is car- 

 bon in the animal part of bone, so it is in all animal sub- 

 stances. It exists in combination with other elements, and 

 therefore does not appear as carbon. It is only by some 

 chemical process which separates it from these combina- 

 tions that it can be made manifest, and combustion is one 

 of the processes that can do this. When animal skin or 

 flesh is charred that is, partially burned the charcoal that 

 appears is produced essentially in the same way that it is 

 when made from wood. It is not really made, but it is sepa- 

 rated by the heat from the substances with which it is com- 

 bined, the heat for the most part driving these off into the 



