C 170 3

gold cannot be got off by either of these ways, the filemust be had recourse to, which takes off more of the me-tal underneath than the turning tool or the scraper, parti-cularly than the former. The gold scrapings or filingsmay be purified from the silver or copper they containby the methods described in the preceding part of thissection.

The editors of the encyclopedic give a method of recover-ing the gold from wood that has been gilt on a water size :this account is extracted from a memoir on the famesubject presented to the academy of sciences by M. deMontamy. The gilt wood is steeped for a quarter of an hour,in a quantity of water, sufficient to cover it, made veryhot: the size being thus softened, the wood is taken outjand scrubbed, piece by piece, in a little warm water, withshort stiff bristle brushes of different sizes, some small forpenetrating into the carvings, and others large for thegreater dispatch, in fiat pieces. The whole mixture ofwater, size, gold, &c. is to be boiled to dryness, the drymatter made red hot in a crucible to burn off the size, andthe remainder ground with mercury, either in a mortar,or, where the quantity is large, in a mill, as describedhereafter, in theeleventh section: some clean sand is directedto be added, which is said to occasion the gold to be easier,laid hold of by the mercury.,

SECT. X.

Of tinging glass and enamel by preparations of gold.

H E tinging of glass and enamels by preparationsJ. of gold appears to have been first attempted aboutthe beginning of the last century, Libavius, whose workscompose a valuable body of the chemical knowledge ofhis own time, conjectures, in one of his tracts entitledAlchymia, printed in 1606, that the colour of the ruby

proceeds