1 616 ]

and on this account only they prefer the dry resin to theliquid glutinous substances.

Page 45, 67. Melting of Gold.

Black lead crucibles are said by foreign writers to beaccompanied with an inconvenience of rendering the goldbrittle and somewhat pale, especially when a new crucibleis used for the first time. I had often melted gold in thesecrucibles myself, and had been told by different workmenthat they generally employed this kind, without observingany ill effect from them. On further enquiry among thegold-beaters, whose daily labour is one of the severest tri-als of the toughness of the gold which they melt, I cannotfind that they have any suspicion of its being injured byblack lead crucibles, though they now make use of theHeffian or English more frequently than the black lead,on account chiefly of their greater cheapness : one ofthese workmen informed me that " he had once foundgold, which was melted in a black lead crucible, to bebrittle, but imagined the brittlenefs to have proceeded onlyfrom want of sufficient heat, for on melting the gold asecond time, in the same crucible, it had the proper tough-ness.” The degree of heat is a very material article in themelting of gold : if the gold is but just brought into fusionit proves always brittle, a pretty considerable increase osthe fire beyond this point being requisite for giving it fullmalleability, or for procuring a perfect solution, and anuniform mixture and cohesion of its parts: and when thisnecessary fluidity has been obtained, the pouring of themetal into a cold mould will render it as brittle as if theheat had been insufficient at first. It is probable that thecafe is the fame in all the other metals, though in no one,perhaps, so eminently as in gold: and we may hence account

for