428 Mr. Stokes on some new double Chromates. 



chrom.ite of silver was of a deep red colour, and when dried 

 weighed 0*6 srain. 



21 '25 : 6-5 : : 0-6 : 0-18 = chromic acid. 

 To the solution which passed through, nitrate of barj-tes 

 was added, sulphate of barytes precipitated, which when heated 

 weighed 54*09 grains. 



14-75 : 5* : : 54'09 : 18-33 = sulphuric acid. 

 The solution was now evaporated to one half, and sulphate 

 and muriate of soda added so as to separate the excess of 

 barytes and silver in solution : the precipitate was separated, 

 and carbonate of soda added to the solution which passed 

 through : carbonate of zinc fell dowUjwhich when dried weighed 

 14-45 grains; 14-2 grains when heated to redness were re- 

 duced to 9-7 grains : 



14-2 : 9-7 : : 14-45 : 9-87 = oxide of zinc. 

 50 grains of the crystals were heated in a small platina cruci- 

 ble over a spirit-lamp, and found to lose 12-6 grains. This 

 was water. By this heat the chromic acid cannot be decom- 

 posed ; but on exposing the dry salt to a strong red heat, an 

 additional loss of 0-1 grain was sustained; and on digesting 

 the dry mass in water, an insoluble precipitate remained of 

 oxide of chrome. To the clear solution 51-5 grains of pure 

 carbonate of potash were added ; the carbonate of zinc was se- 

 parated, and the solution evaporated to dryness : sulphuric 

 acid was then added to decompose all the carbonate of potash, 

 and the whole again evaporated to dryness ; the salt obtained 

 when dried was found to weigh 81-05 grains. 



11 : 6 :: 81-05 : 44-2 potash. Of this 44-2, 35-31 grains 

 belong to the carbonate of potash added ; for 



8-75 : 6 : : 51-5 : 35-31— then 44-2 — 35-31 = 8-91 the 

 potash of the salt. 



f Sulphuric acid . . . . 18*33 

 j Chromic acid 0-18 



. , - 1 Oxide of zinc 9-87 



Analysis. ^ ^^^^^ g.^^ 



j Water 12*60 



\^Loss 0-11 



50-00 grains. 

 In preparing chromate of nickel, I mixed chromate of pot- 

 ash and sulphate of nickel in the atomic proportions. At 

 first no precipitate took place ; but on heating the solution, the 

 chromate of nickel fell down copiously. To insure its total 

 separation the solution was boiled to dryness, the residuum 



digested 



