CARBON AM) THE II YI>K< ( 'AJUV 337 



luminous rays (clue to its blackness and opacity), and many other quali- 

 ties are familiar from everyday experience. 11 The specific gravity of 

 charcoal varies from T4 to 1-9, and that it floats on water is due to the 

 air contained in its pores. If charcoal be reduced to a powder and 

 moistened with spirit, it immediately sinks in water. It is infusible in 

 the furnace and even at the temperature of the oxyhydrogen flame. In 

 the heat generated by means of a strong galvanic current, charcoal 

 only softens, but does not completely melt, and on cooling it is found 

 to have undergone a complete change both in properties and appearance, 

 and is more or less transformed into graphite. The physical stability 



slightly porous, brilliant, does not soil or mark paper, is dense, almost devoid of the faculty 

 of retaining liquids and solids, and does not absorb gases. The light sorts of charcoal 

 produced from charred wood, on the other hand, show this absorptive power in a most 

 marked degree. This property is particularly developed in that very fine and friable 

 charcoal prepared by heating animal substances, such as hides and bones. The absorp- 

 tive power of charcoal with reference to gases, is similar to the condensation of gases in 

 spongy platinum. Here evidently there is a phenomenon of the adherence of gases to a 

 solid, precisely as liquids have the property of adhering to various solids. One volume 

 of charcoal will absorb the following volumes of gases (charcoal is capable of absorb- 

 ing an immense amount of chlorine, almost equal its own weight) : 



The quantity of gas absorbed by the charcoal increases with the pressure, and is 

 approximately proportional to it. The quantity of heat given out by the absorption 

 nearly approaches that set free on dissolving, or passing into a liquid condition. 



Charcoal absorbs not only gases, but a number of other substances. For instance, 

 alcohol, which contains disagreeably smelling fusel oil, on being mixed with charcoal or 

 filtered though it, loses the bulk of the fusel oil. The practice of filtering substances 

 through charcoal in order to get rid of foreign matters is often applied in chemical and 

 manufacturing processes. Oils, spirits, various extracts, and vegetable and other solu- 

 tions containing an admixture of colouring or odorous matters, and also water, are 

 filtered through charcoal in order to purify them. The bleaching power of charcoal 

 may be tested by using various coloured solutions such as aniline dyes, litmus, &c. 

 Charcoal, \\liicli has absorbed one substance to saturation, is still capable of absorbing 

 certain other substances. The more porous charcoal is, the greater its surface, and this 

 is the reason why animal charcoal, produced in a very finely-divided state, especially by 

 h.-iiting bones, makes the best sort for the purposes of absorption. Bone charcoal is 

 used 'in large quantities in sugar works for filtering syrups, and all saccharine solutions, 

 in order to purify them, not only from colouring and odorous matter, but also from lime. 

 \vhich is mixed with the syrups in order to render them less unstable during boiling> 

 The absorption of lime by animal charcoal depends, in all probability, in a great degree 

 on the mineral component parts of bone charcoal. 



11 Charcoal is a very bad conductor of heat, and therefore forms an excellent insulator 

 or packing to prevent the transmission of heat. A charcoal lining is often used in 

 crucibles for heating many substances, as it does not melt and resists a far greater heat 

 than many other substances. 



VOL. I. Z 



