Factor for potassium Relation to factor chlorid from 0.30557 in per cent Atomic Determined weight of or Potassium Potassium Platinum. calculated platino- Platinum. platino- Platinum. by chlorid. chlorid. 197.18 Berzelius 0.30557 0.75658 100.00 100.00 197.88 Andrews 0.30517 0.75390 99.86 99.65 195.06 Haberstadt 0.30690 0.76468 100.44 101.07 Seubert } 194.87 and Clark } 0.30700 0.76555 100.47 101.20 The factor 0.3056 is regarded as the best for the computation from potassium platinochlorid and 0.7566 from platinum. It is also suggested that it is better to make the computation from the reduced platinum than from the double salt. =269. Recovery of the Platinum Waste and Preparation of the Platinic Chlorid Solution.=—(1) _By Reduction in Alkaline Alcohol._—All filtrates containing platinic chlorid, all precipitates of potassium platinochlorid and all residues of metallic platinum should be carefully preserved and the platinum recovered therefrom by the following process: The platinum residues are placed in a large porcelain dish. Since these residues contain a large amount of alcohol they should be diluted with about one-third their volume of water, and when boiling treated with some sodium carbonate. The solid potassium platinochlorids should not be added until the liquid is boiling, and then only little by little. The heating on the water-bath is continued until the liquid floating over the platinum sponge is quite clear and only slightly yellow. The liquid is then poured off and the reduced platinum purified by boiling with hydrochloric acid and water. It is then dried and ignited to destroy any organic matter which may be present. It is advisable to boil the finely divided platinum once with strong nitric acid, and after this is poured off the solution of the platinum is effected in a large porcelain dish over a water-bath by adding about four times its weight of hydrochloric acid, warming, and adding nitric acid, little by little. After the platinum is in solution the evaporation is continued until a drop of the liquid, removed by a glass rod, quickly solidifies. The crystalline mass which is formed on cooling is taken up with water and filtered, and then a sufficient amount of water added so that each ten cubic centimeters will contain one gram of platinum. The specific gravity of this solution is 1.18 at ordinary temperatures. Special care must be taken that the solution contains neither platinous chlorid nor nitrogen compounds. If the first named compound be present it should be converted into platinic chlorid by treatment with fuming hydrochloric acid and a little nitric acid.