340 DR DAVY ON THE PROPERTY OF CHARCOAL AND PLUMBAGO 



they are connected solely with difference of mechanical arrangement. The trans- 

 parency of the minute portions of charcoal and plumbago, assimilating them to 

 the diamond, may be considered as not unfavourable to this latter view, which is, 

 I believe, the one now commonly adopted, especially taking into account the dif- 

 ference of magnitude between the plates and particles described, possessing the 

 property of translucency, and the atoms, or ultimate particles, the subject of che- 

 mical action, and probably of crystalline aggregation. A piece of goldbeater's 

 skin, an inch square, before it was reduced to charcoal, weighed .36 grain, and, 

 when reduced, only .03 grain ; and yet a portion of this, not exceeding in size a 

 single red particle of the blood of man, might be seen under the microscope to 

 consist of several parts : a cylindrical piece of the charcoal of the pith of the elder, 

 A of an inch long, and .2 of an inch in its transverse diameter, weighed only ^th 

 of a grain, and yet it was composed of a vast number of plates of large dimen- 

 sions, microscopically considered, one of them being capable of covering more than 

 a hundred of the smaller particles which abound in and seem to form the basis of 

 chyle. 



The translucency of charcoal or carbon, in a very finely divided state, and its 

 effect on light, may help to account for the colour of flame and of luminous bodies 

 seen through the medium of smoke, and also for the colour (different tints of 

 brown) exhibited by fluids in which carbonaceous matter is suspended, as when 

 sulphuric acid is heated with alcohol ; or charcoal in impalpable powder, such as 

 lamp-black, is mixed with a solution of gum. In the former instance, it is not 

 improbable that the brown colour of the fluid may be owing chiefly to particles 

 of carbon suspended in it, so small as to be invisible even when the eye is aided 

 by the highest power of the microscope. This conjecture is in accordance with 

 the fact, and indeed was suggested by it, that the coloured fluid, which, seen by 



The specific gravity of plumbago is stated to range between 1.987 and 2.456. A specimen of the 

 compact kind, from Borrowdale, I found of sp. gr. 2.264, and after the exhaustion of adhering air, by the 

 air-pump, 2.316. A specimen of the foliated kind, I found of the sp. gr. 2.22, and after having been sub- 

 jected to the action of the air-pump, 2.26. The former yielded, on incineration, 11.48 per cent, of ash, 

 retaining the form of the mass, of a light ochre yellow, which was found to consist chiefly of silica, with a 

 little peroxide of iron, and a very little alumine, with a trace of lime and magnesia. The latter being 

 incinerated with great difficulty, was deflagrated in red hot nitre ; it yielded 4 per cent, of ash, which 

 was found to consist chiefly of silica and peroxide of iron, with a little lime and magnesia. The ash was 

 in the form of a powder of fine scales. If the iron and silicon exist in plumbago uncombined with oxygen, 

 their presence may account for the specific gravity of the mineral exceeding that of charcoal and anthra- 

 cite ; but, if combined with oxygen, then it must be admitted that the carbon in plumbago is in a denser 

 state than in charcoal. The circumstance that plumbago is slightly magnetic is in favour of the first idea, 

 and also the fact, as I have ascertained, that it yields air (which it may be presumed is hydrogen) when 

 acted on by dilute sulphuric acid previously purged of air by the air-pump, and after which iron may be 

 detected in solution. 



