He next tested the silver grains which he had brought from the river. His method was a very simple one, invented by himself. It consisted in filling a clay cup with water and weighing it, then weighing a quantity of the metal, and then putting this metal in the water and weighing the whole. A simple mathematical calculation from these three weights gave him the specific gravity of the metal. This process was repeated a number of times to avoid error, and gave as an average the figure 21.5, which he remembered to be the specific gravity of pure platinum.
As a further test he hammered some of the supposed platinum into a thin sheet, and attempted, without success, to melt it. Then he laid a sliver of one of his lead bullets on it, and tried again, with the result that the lead melted and burned a hole through the metal sheet. This test convinced him that he truly had found platinum.
Cabot next turned his attention to glass making. For ordinary glass he would need quartz, soda, potash, and limestone.
The reason for his employing both soda and potash instead of merely one or the other, was that together they would have a lower fusing point, and thus be easier for him to handle with his crude equipment. For glass for his tubes he would use litharge in place of the limestone.
The quartz and the limestone were already available. Soda would be a byproduct of his sal ammoniac when he got around to making it, but this would not be until he had made sulphuric acid from his copper ore, which was a most complicated process as he remembered it.
Potash could be got simply by dripping water through wood-ashes, evaporating the water, roasting the sediment, dissolving again in water, letting the impurities settle, and then evaporating the clear liquid, and roasting again. He started this process at once.
But he had no idea how to make litharge. Furthermore, he could not blow his glass until he had metal tubes, so he abandoned further steps for the present.
While he was pondering over these problems a messenger arrived, demanding his immediate presence at the quarters of Jud the Excuse-Maker.
Jud was in a state of great excitement when the earth-man arrived.
Said Jud: “Do you remember what you told me about the beasts of the south, who swim through the air, talk soundless speech, and use magic slingshots like yours which you captured from the Roies near Sur?”