iji the Distillation of f Food, ^c. 273 



In numerous trials to combme iron with charcoal so as to 

 form this substance, I have uniformly failed of success, except 

 where, as in the case above related, the charcoal or carbon hiis 

 been in a state of previous coinbinatiori, or was actually held in 

 solution. In many trials on tliis principle, the results have been 

 tolerablv successful. If therefore we are to adopt an igneous 

 theorv of the formation of plumbago, it will be as easy to sup- 

 pose that the action of subterraneous fire on mixtures of bitu- 

 men and iron has produced the compound of charcoal and iron, 

 on the jjrinciples I have described, and this supposition will be 

 more consonant to the chemical facts. But we are too little 

 acquainted with the geological relations of plumbago to lay much 

 stress at present upon this or any other hypotbesis. It is evi- 

 dent that plumbago mav be a produce of art; and could it be 

 produced in as solid and compact a state as Nature affords it, 

 the discovery would form a material addition to those useful ones 

 for which the arts have been indebted to chemistry. 



As nothing tends more to confusion of ideas than confusion 

 of terms, I may be excused for proposing a name to the pitch of 

 distilled wnod, a name in familiar use, though hitherto unappro- 

 priated bv chemists. It is in fact tliat which is well known to 

 painters by the name of bistre, although the nature of bistre has 

 I believe never vet been examined ; and the importance of it to 

 the arts of design induces me to extend tins article for a few 

 lines. According to Dr. Lewis, bistre is produced from the soot 

 of all \\0()d, other receipt books give us the same account, but 

 limit the sort of wood to beech without seeming aware of its real 

 nature; but the colourmen use the soot of all wood indiscrimi- 

 nately. 



Tliose artists who have made the tour of the highlands of 

 Scotland, are well accpiainted with tbat variety of it which var- 

 nishes the interior of a highland cottage. 



- In all these cases it is a very variable article ; .ind the colour- 

 maker, being unac(]uainted v/ith its real nature, is unable to rectify 

 its faults ; in conse(|uence of which it is often unfit for use, not- 

 withstanding the various operose and mysterious purifications it 

 undergoes in hi-- workshop. The causes of these varieties will 

 be verv evident to those who have read the foregoing experi- 

 ments. An imperfect separation of essential oil and a con'e- 

 quent tenacity arising from its too near alliance to the tar, will 

 appear to be its iiiost conmion vice, and it is this which gives it 

 that disagreeable oumminess and disposition to return to the 

 ))encil which is destructive of its best qualities. At times also 

 from the sajnc causes it is offensively vcllow. So valuable is a 

 brown colour that will work freely and with transparency, that 

 the artists will be nmch obliged to him who shall render bistre 

 Vol. 45. No. 203. April I'SIS. S equal 



