POTASSIUM CHLORO-PLATINITE (Formula, —Takes the form of reddish deliquescent crystals, very soluble in water, but slightly in alcohol. It should dissolve in water without any residue and give a neutral solution. Messrs. Pizzighelli and Htibl in their work on the platinotype process give the following instructions for its manufacture : "Take 5o grammes of platinum chloride (chloroplatinic acid), dissolve in zoo c.c. of pure water, and filter if necessary; then heat to zoo degrees C. in a water bath, and pass through it a strong stream of washed sul phurous acid gas. After a while the yellow liquid will begin to assume the characteristic red color of the platinous chloride. The liquid has then to be tested from time to time to watch its progress. A little is taken on the end of a glass rod and mixed with a little ammonium chloride on a watch glass ; the presence of any unreduced or platinic chloride is shown by the formation of an insoluble yellow precipitate of chloroplatinate of ammonia. The quantity of this precipitate that is formed should be noted, as one can judge from this of the amount of reduction that is going on. When the precipitate begins to form but slightly, the stream of gas should be checked so as to have the operation well under control, and as soon as the liquid ceases to give a precipi tate the gas stopped completely. The reason for this is that if allowed to continue the gas would comMence to attack the platinous chloride form, and further convert it to a platinous sulphide, a salt not reducible by ferrous salts. On the other hand, if the action be stopped too soon, platinic chloride will be left, and in the further operations would be thrown down as an insoluble salt.
Hence care is necessary in the above operations.
"The solution that is obtained consists of a mixture of platinous chloride, sulphuric and hydro chloric acids. To convert this into the double salt it should, after cooling, be poured into a porcelain basin, and a hot solution containing 25 grammes of chloride of potassium in 5o c.c. of water well mixed with it by stirring. The chloroplatinite then separates in the form of a crystalline deposit and is collected on a filter, the mother liquor being drained off ; it is then washed with a little water, and then a little alcohol, until the last washing gives no acid reaction.
"The powder is now spread out on filtering paper and left to dry in a dark room, as the salt when moistened with alcohol is reduced by the action of light. Salt thus prepared is per fectly pure and can be used at once. Seventy-four or seventy-five grammes of the double salt should be obtained from each zoo grammes of platinic chloride, this being about 93 per cent. of the theoretical quantity. No effort need be made to obtain from the mother liquor a still further quantity of potassium chloroplatinite." Potassium chloroplatinite is employed in photography in the platinotype process, owing to the fact that ferrous oxalate reduces it to metallic platinum. The action is thus expressed : 6Fe C, 3K, PtC1; = 2Fe, (C, + Fe, Cl, x 6KC1 + 3Pt.