[ 5 2 5 ]

even when the silver amounted to twenty times the weightof the platina ; but one part of platina with thirty of silvermade a mixture as white as the silver itself. None ofthem seem to have tarnished or changed their colour inkeeping.

IX. Platina with Gold.

The near and remarkable relation betwixt platina andgold in many properties hitherto supposed to belong togold alone, their as manifest disagreement in others, andthe reports of gold having been debased by the admixtureof considerable quantities of platina, induced me to exa-mine more particularly the effects of these two metals incombination with different proportions of one another.The proportions were adjusted according to the caratweights, as explained in the seventh section of the historyof gold, the fineness of gold being usually expressed incarats and their subdivisions. The absolute weight ofwhat in these experiments is called a carat, was fourgrains.

i. Twelve carats of fine gold, and the same quantity ofthe purer grains of platina, were urged in a blast furnacefor near an hour, with a fire so strong, that the slip ofWindsor brick with which the crucible was covered,though it had been dipt in thin tempered Sturbridge clay,begun to melt. Upon breaking the vessel, the metal wasfound in one smooth lump or bead, which being nealedby the flame of a lamp, and boiled in alum water (the li-*quor commonly used by the workmen for cleansing orbrightening masses of gold and silver) appeared, both inthe mass and upon the touchstone, of a pale bell-metalcolour, without any resemblance to gold. It bore severalstrokes, and stretched considerably under the hammer, be-fore it began to crack about the edges. On viewing thefracture with a magnifying glass, the gold and platina ap-

Y y y 2 peared