336 DR DAVY ON THE PROPERTY OF CHARCOAL AND PLUMBAGO 



of common charcoal. I may add, they were found in mass to conduct electricity. 

 I may observe, further, in confirmation of what has just been stated, that I could 

 detect no material difference in the charcoal, as regards the translucency of its 

 plates, after it had been subjected to boiling in distilled water and in dilute mu- 

 riatic acid ; nor, in a specimen prepared from the pith of the elder similarly treated, 

 and boiled also in alcohol previously to charring, nor after the charcoal had been 

 ignited a second time ; if any difference existed, it was in favour of the purified 

 portions. 



Inferring that the charcoal of the pith of the elder owes its transparency 

 under the microscope to the thinness of its plates, I expected to find the same pro- 

 perty exhibited by charcoal generally, in a finely divided state ; and the trials I 

 have made of different specimens have not disappointed me. The notice of a few 

 examples may suffice. 



The pith of the annual shoot of the sycamore, is very similar in structure to 

 that of the elder ; and the plates of which it consists, when reduced to charcoal, 

 exhibit, under the microscope, a similar appearance, though not quite so distinct. 



The pith of the rush is formed of radiating fibres, ^ooth mcn m diameter and 

 under, five or six of which commonly proceed from a common centre, and which 

 are occasionally connected by a membrane or plate of extreme thinness. When 

 charred, the fibres, by transmitted light, appear of a brownish hue, and some of 

 them allow lines on the glass-support to be seen obscurely. The plates, by re- 

 flected light, appear almost white ; by transmitted light brown or grey ; through 

 them, lines on the glass may be seen distinctly. 



The charcoal of cotton shews the fibre of this substance in a very clear 

 manner, varying in diameter from jgogth to ^ooo^h mcn > flattened, ribbon-like, and 

 twisted at intervals.* The finer fibres, and the flat part of the larger, free from 

 torsion, exhibit a certain degree of transparency under the microscope, although 

 they do not allow lines to be seen through them, unless they have been wasted 

 in a certain degree in the fire during the process of carbonization ; the larger 

 fibres, especially when twisted, are almost black, and nearly, if not quite, opaque. 



The charcoal of linen-thread, and flax, equally well shew the form of the 

 fibre of this substance, which is so characteristic. Smaller than the fibre of the 

 cotton, varying in thickness from ggggth to zmfi*- f an inc h cylindrical, without 

 any twist, it appears to be more dense than the fibre of the cotton, and is in a less 

 degree translucent, indeed, it is difficult to find a fibre of the charcoal made 

 from the finest cambric, that transmits light with tolerable distinctness. 



* Mr BAUER, in the account he has given of the microscopical appearance of cotton, appended to the 

 " History of the Cotton Manufacture in Great Britain," by E. BAINES jun., Esq., describes the twisted 

 appearance of the fibres as being often owing to the junction and torsion of two fibres : this I have never 

 witnessed, and I am induced in consequence to question the correctness of the observation ; Mr BAUER 

 may have been deceived by using a microscope of indifferent construction. 



