There is a substance, the double nitrate of silver and thallium, which, while solid at ordinary temperatures, liquefies at 750 C. and then has a specific gravity of 4-5. Admixture with water lowers the density to any desired point.
If a glass cell is taken containing this liquid diluted to a density of about 3-6, and in it is thrown pieces of the above-named minerals, all those whose density is lower than 3-6 will rise to the surface, while the denser minerals will sink. If now a little water is carefully added with constantly stirring until the density of the liquid is reduced to that of the diamond, the heterogeneous collection sorts itself into three parts. The graphite, quartz, beryl, mica, and hornblende rise to the surface ; the garnet, corundum, zircons, etc., sink to the bottom, while the diamonds float in the middle of the liquid. With a platinum landing-net I can skim off the swimmers and put them into one dish ; with the same net I can fish out 94