Ambergriſe, according to the aſſertion of Mr. Aublett, is nothing more than the juice of a tree inſpiſſated by evaporation into a concrete form. This tree grows in Guyana, and is called Cuma, but has not been inveſtigated by any botaniſt. Pieces of this tree are ſaid to be carried down into the rivers by heavy rains, and the ſpecimens examined by Mr. Rouelle had the odour and principal qualities of amber[[50]]. Rumphius, long ſince, mentioned a tree called Nanarium, whoſe juice reſembled amber[[51]].
DIAMOND.
At firſt ſight I may ſeem to have acted erroneouſly, by ſeparating this from the other gems, and inſerting it here; but after due conſideration, I know not where to place it better. It has never yet been decompoſed by the liquid analyſis[[52]]; and when expoſed to the fire in an open veſſel, it is wholly conſumed, burning with a lambent flame. This deflagration, though ſlow, ſhews decidedly its affinity to the inflammables: beſides, in the focus of a burning glaſs, it leaves traces of ſoot[[53]]. When further experiments teach us better, I ſhall willingly correct my error.
CLASS IV.
METALS.
I have before mentioned the great affinity betwixt metallic and inflammable ſubſtances (§ 133). Zinc and arſenic stand, as it were, upon the borders betwixt them; for these, in proper circumſtances, burn with a very evident flame. All the metallic ſubſtances contain phlogiſton, and when, to a certain degree, deprived of it, fall into a powder like an earth; but their attractions for phlogiſton are different. Moſt of them, when melted in a common way, and expoſed to the air, have an earthy cruſt formed upon the ſurface, which cannot again be reduced to metal without the addition of ſome inflammable matter. The baſe metals, eleven in number, have this property: but the noble metals, platina, gold and ſilver, are ſo firmly connected to the phlogiſton, that they never calcine under fuſion, however long continued; and after being changed into a calx in the liquid way, when melted in the fire, they re-aſſume their metallic form, without any other phlogiſton than what is contained in the matter of heat.
Quickſilver holds a kind of middle place; for, like the baſe metals, it may be calcined, though not readily; and like the noble ones, it may be reduced by heat alone.
I have placed each diviſion of the metals in the order of their specific gravities.