[ 339 ]

that the choice of the vegetable subject affects rather thesoftness or hardness than the colour of the coal.

After examining the different substances of the vege-table and animal kingdoms, I tried a mineral body, pitcoal;of which several pieces, of different forts, were charredin close crucibles. The charred coals, reduced into finepowder and used as paints on paper, shewed nothing ofthe brownish hue which the unburnt pitcoal had whentried in the same manner, all of them inclining to bluish,and most of them having this cast in a greater degree thanany of the vegetable coals. The blue-black of the shopscannot however be of this origin, the ashes of the charredpitcoal not being dissoluble by the vitriolic acid, as thoseof the blue-black were found to be.

II. Soot blacks..

The foot blacks are in general much softer and of amore yielding texture than those of the charcoal kind, andrequire much less grinding for uniting them with oily,watery or spirituous liquors, into a smooth mass: of some ofthem a part is dissolved by water or spirit of wine, whilenone of the charcoal blacks have been found to contain anything dissoluble.

This soluble matter of soot is not however black likethe indissoluble parts; and in this particular, as well as inthe colour of the entire mass, different forts of foot differfrom one another. Thus the scot of pitcoal collected incommon chimneys, of itself rather greyisst-black than ofa full black, being infused separately in rectified spiritof wine and in water, tinged the former of a transparentreddish colour, and the latter of a paler reddish; while thedeeper black foot of wood, both to spirit and to water,gave an opake dark brown.

Yy

From,