#

[ 568 ]

had been unable to produce. They put upon a. cupel ofa proper size one ounce of platina and two ounces of lead,and having placed the cupel in a furnace like that ofMr. Pott for the vitrification of earthy bodies, they raisedthe fire by degrees, and kept it up without intermiflionfor fifty hours, in such manner, that during the last twenty-four hours it continued in its full violence. The cupelbeing then taken out, they found that the platina, insteadof being in a round brilliant button as gold and silver areafter cupellation, was extended and flattened on the cupel:its upper surface was tarnished, dark coloured and wrinkled,from whence it was judged at first that the operation hadsucceeded no better than those we have been speaking of:the platina parted easily from the cupel, which was becomevery hard, of a yellowish white colour, semitransparent,and struck fire freely with steel. But upon exactly weigh-ing the platina, they found, that instead of receiving anaugmentation of weight from some of the lead remainingundestroyed, it had lost one sixteenth of its weight: itslower surface was white and silvery: finally it was noteager, but bore very well to be extended under the ham-mer: they dissolved a part of this cupelled platina in aquaregia, and this dissolution did not shew any vestige of lead/'As Mr. Macquer appears to have employed in this ex-periment the platina such as he received it, containing alarge admixture of ferrugineous and other foreign mattersundoubtedly destructible in the process; it is obvious thatit might have retained a very considerable proportion of thelead, notwithstanding the diminution in.-weight. Nor canaqua regia be looked upon as an infallible test of its havingbeen pure from lead; for this menstruum, in certain cir-cumstances, will dissolve lead as well as platina. Butwhatever might be in this, the event of the experiment, inregard to the malleability of the cupelled mass, appeared

too