The preceding compositions, after being gently hammered and boiled, were weighed hydrostatically with great care, by a very tender balance, in distilled water, wherein the gravity of standard gold turned out 17.788.
All the mixtures proved heavier than standard gold. Their gravities were nearer to the medium of the gravities of the ingredients, than those of the compositions of platina with any of the other metals formerly given an account of; none falling considerably short of the mean gravity, and some rather exceeding it.
| Gravity. | ||||||
| By Experiment. | By Calculation. | Difference. | ||||
| Platina | 17.000 | |||||
| Platina 1 | Gold 1 | 18.140 | 18.142 | 0. 02 | } Diminution. | |
| Platina 1 | Gold 3 | 18.613 | 18.714 | 0.101 | ||
| Platina 1 | Gold 5 | 18.812 | 18.904 | 0.092 | ||
| Platina 1 | Gold 11 | 18.835 | 19.094 | 0.259 | ||
| Platina 1 | Gold 15 | 18.918 | 19.142 | 0.224 | ||
| Platina 1 | Gold 23 | 19.089 | 19.189 | 0.100 | ||
| Platina 1 | Gold 31 | 19.128 | 19.213 | 0.085 | ||
| Platina 1 | Gold 47 | 19.262 | 19.237 | 0.025 | } Increase. | |
| Platina 1 | Gold 95 | 19.273 | 19.261 | 0.012 | ||
| Gold | 19.285 | |||||
Experiment III.
As a mixture of platina with an equal quantity of gold has been reported to be specifically heavier than gold itself, but turned out otherwise in the above experiments; some further trials were made on that head.
1. Instead of the crude mineral, whose gravity is but 17, we took platina, that had been cupelled with lead, one of the neatest of the buttons formerly mentioned, which, tho' retaining a portion of the lead, was nearly as ponderous as fine gold, viz. 19.240. This was melted with equal its weight of the gold, in a strong fire, and continued in fusion for about an hour: the mass proved spongy, and very light. We remelted it several times with vehement degrees of fire, suffering it to cool leisurely in the crucible, and, in order to separate as much as possible of the lead, to which its sponginess seemed owing, boiled it in aqua-fortis, and repeatedly injected corrosive sublimate upon it during fusion: the mass, nevertheless, still turned out cavernulous and brittle, and specifically lighter than either the gold or platina by themselves.
2. I likewise endeavoured to combine platina with small proportions of gold. By vehemence of fire, it was made to unite, tho' not perfectly, with half its weight and less: but the mixtures were extremely spongy and brittle; in specific gravity one scarce 16, another less than 15.
3. As a cast metalline body from the Spanish West Indies, of which some account will be given hereafter, appears to have been confounded with the mineral platina, this also was melted with an equal quantity of gold. They united with great ease, by a moderate fire, into an uniform compound, tolerably compact, but whose specific gravity was only 16½; which is nearly the mean gravity of the two ingredients.
Experiment IV.
As a small portion of copper somewhat heightens the colour of pale gold, platina was melted with eight times its weight of standard gold made with copper alloy. The fusion was performed, as in the preceding experiments, in a close crucible, with a strong fire, but without any flux, and continued for about an hour. The metal appeared covered with a black scurf, and had lost about ⅟200. It was much duller coloured, harder to the hammer, and cracked sooner about the edges, than mixtures of fine gold with a larger quantity of platina. By repeated fusion, and frequent nealing, it became a little softer and tougher, so as to be drawn into pretty fine wire; but the colour was still exceeding dull, more resembling that of bad copper than of gold.