Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/37

Rh 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 wood, a name in familiar use, though hitherto unappropriated by chemists. It is in fact that which is well known to painters by the name of Bistre, although the nature of bistre has I believe never yet been examined; and the importance of it to the arts of design induces me to extend this article for a few lines. According to Dr. Lewis, bistre is produced from the soot of all wood, 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 indiscriminately.

Those artists who have made the tour of the highlands of Scotland, are well acquainted with that variety of it which varnishes the interior of a highland cottage.

In all these cases it is a very variable article, and the colour-maker being unacquainted with its real nature, is unable to rectify its faults, in consequence of which it is often unfit for use, notwithstanding the various operose and mysterious purifications it undergoes in his workshop. The causes of these varieties will be very evident to those who have read the foregoing experiments. An imperfect separation of essential oil and a consequent tenacity arising from its too near alliance to the tar, will appear to be its most common vice, and it is this which gives it that disagreeable gumminess and disposition to return to the pencil which is destructive of its best qualities. At times also from the same causes it is offensively yellow. So valuable is a brown colour that will work freely and with transparency, that the artists will be much obliged to him who shall render bistre equal in freedom and force to seppia. By distilling

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