Chemical Science, 477 



occasioned. The fluid was then perfectly free from arsenic. The 

 precipitate was pure sulphuret of arsenic, soluble in ammonia 

 when slightly heated, and composed of equal parts of sulphur and 

 the metal. 



M. PfafT further says that arsenic acid may be separated from its 

 combinations with bases, by dissolving the arseniates in nitric acid, 

 and passing sulphuretted hydrogen through the solution ; an abun- 

 dant precipitate of sulphuret of arsenic is formed, containing no trace 

 of the base of the arseniate decomposed. — Bull. Univ,A, viii. 256. 



24. New Double Chromates. — Mr. Stokes has obtained several 

 new salts, by mixing chromate of potash with metallic sulphates. 

 Chromate of potash, mixed with sulphate of zinc, gave a precipitate 

 of chromate of zinc; and the mother liquor, by concentration, yielded 

 certain yellow crystals in the form of a flat rhombic prism, which 

 Dr. Thomson had mistaken for impure sulphate of zinc, but which 

 Mr. Stokes recognised as a new compound: 50 grains gave 18.33 

 sulphuric acid ; 0.18 chromic acid ; 9.87 oxide of zinc; 8.91 potash; 



12.6 water; 0.11 loss. 



Chromate of potash and sulphate of nickel were mixed in atomic 

 proportions, and the solutions heated; after the chromate of nickel 

 was separated, they were evaporated to dryness. The residuum, di- 

 gested in water, was filtered, and the deep red solution obtained upon 

 cooling, yielded grass green crystals in the form of oblique rhombic 

 prisms; 50 grains of these, when analysed, gave 12.26 sulphuric 

 acid; 0.978 chromic acid; 8.2 oxide of nickel ; 9.862 potash; 



12.7 water. 



A similar salt may be obtained by mixing chromate of potash 

 and sulphate of copper. It is of a light green colour, and has pre- 

 cisely the same form as the salts already described. In every case 

 crystals of bichromate of potash were produced in the second crop 

 crystals.— P^i/. Mag. N. S. ii. 427. 



25. Dobereinei^s finely divided Platina. — 'The following is |M. 

 Dobereiner's process for obtaining finely divided platina, fit for the 

 performance of the experiment wliich he first made on the combi- 

 nation of oxygen and hydrogen, at common temperatures. Mix 

 muriate of platina with a solution of neutral tartrate of soda in a 

 glass tube, half or three-quarters of an inch in diameter, and twenty 

 or thirty inches in length, and apply heat until the fluid becomes 

 slightly turbid ; aft^erwards expose it for several days to the sun's 

 rays. The greater part of the platina will separate from the solu- 

 tion, and be deposited in minute laminae, of a greyish black 

 colour on the sides of the glass ; the tube and its contents are to 

 be put into a glass vessel containing water, and it is to be filled 

 with hydrogen gas ; the platina becomes almost immediately white 

 and shining like silver, and may then be readily detached from the 

 glass. During the reduction of the platina the tartaric acid is partly 

 converted into carbonic and formic acids. ** As the inflamma- 



OCT.— DEC. 1327. 2 I 



