[ H6 ]

The process of testing is often performed in the famemanner as that of cupellation : but where great quantitiesof base metal are to be worked off from a little gold, re-course is had to a more expeditious method, that of testingbefore the bellows.

An oval test is placed in a cavity, made in a hearth of aconvenient height, and some moistened sand or ashespressed round it to keep it steady : the nose of a bellowsis directed along its surface, in such a manner, that ifashes are sprinkled in the cavity of the test, the bellowsmay blow them completely out : some have an iron platefixed before the bellows, to direct the blast downwards.To keep the surface of the test from being injured in put-ting in the metal, some clothes or pieces of paper are in-terposed. The fuel consists of billets of barked oak, laid onthe sides of the test, with others laid crosswise on these ;the bellows impels the flame on the metal, clears the sur-face of ashes or sparks of coal, hastens the scorification ofthe lead, and blows off the scoria, as fast as it forms, toone end of the test, where it runs out through a notchmade for that purpose. About two thirds of the scorifiedlead may thus be collected, the rest being partly absorbedby the test, and partly dissipated by the action of thebellows. Care must be taken not to urge the blast toostrongly, lest some portion of the gold should be carriedaway by the fumes impetuously forced off from the lead,and some minute particles of it entangled and blown offwith the scoriæ.

In the history of the French academy of sciences forthe year 1727, a process is given for purifying a particularkind of debased gold, which is said to be quite brittle andintractable, not to flow thin enough to be poured com-pletely out of the crucible, to appear on the surface of alivid hue, and which is supposed by du Fay and Hellot to

receive