500 Mr. W. N. Hartley on a new Chromic Oxalate. [Nov. 27, 



racter,and its optical properties. It has the formula *^,„ J 3C 2 4 .4H 2 0, 



and must therefore be called potassio-calcium chromic oxalate. 



Preparation. — a. By mixing the blue potassium chromic oxalate with 

 calcium chloride : the solutions should be dilute and warm. The salt is 

 deposited in crystals. 



Or 2 '" } 3C 2 (0 4 ) + Ca"Cl 2 = K g,',', } 3C 2 (0 4 ) + 2K 01, 



h. By boiling a solution of red potassium chromic oxalate with freshly 

 precipitated calcium oxalate, a solution is made which deposits the new 

 salt, after the following equation : — 



Cr'" } 2(C 2 4 )+C a "C 2 4 = } 3(C 2 4 ). 



The former method is preferable. 



It was noticed that the crystals became opaque and of a greenish- violet 

 tint when dried over sulphuric acid, though their general appearance is 

 of a brilliant greenish-black lustre. A basinful of crystals was then 

 divided, one portion being dried by pressure between folds of filter-paper, 

 and the other by standing in a desiccator for thirty hours ; the difference in 

 appearance previously noticed became evident. Desiccation in vacuo 

 over sulphuric acid, as well as heating to 100° C, renders these crystals 

 anhydrous ; and they have then a decidedly violet colour, with a silky 

 lustre ; exposure to the air even while being weighed renders them green 

 again, the green tint commencing at the edges, which shows that they 

 readily reabsorb water. The analysis of the salt was made by fusing it 

 with 2 j times its weight of a mixture of equal parts of sodium carbonate 

 and potassium nitrate. The filtrate was in some cases neutralized with 

 acetic acid, acidulated with nitric acid, and the chromium precipitated as 

 mercurous chromate, and ignited as usual ; in other cases the chromate 

 was reduced with a drop or two of an alcoholic solution of sulphurous 

 oxide, and the sesquioxide precipitated by ammonia. The potassium was 

 estimated by fusing the salt alone, dissolving in hydrochloric acid, and 

 precipitating with platinic chloride. 



Analysis. 



Weight of salt. Dried over 



grm. H 2 S0 4 . H 3 lost. 



1 1 0-961 3-9 percent. 



II.. ... 1 0-960 4-0 



Heated to 100° C. 



H 2 O lost. Total water. 



1 0-879 12-1 per cent. 16-00 per cent. 



II 0-879 12-1 „ 16-10 „ 



