Brown in g an d Flora — Ceric Ch rom ate. 1 77 



Art. XVI. — On Ceric Chromate ; by Philip E. Brownlng- 

 and Charles P. Flora. 



[Contributions from the Kent Chemical Laboratory of Yale University — CXIV.] 



Bohm* in a recent paper descriptive of his thorough investi- 

 gations of the application of chromic acid to the separation of 

 the cerium earths, states that when the mixed oxides of cerium 

 lanthanum and didjmium are brought in contact with a calcu- 

 lated amount of chromic acid, a little water added, and heat 

 applied for a time, an orange red amorphous powder remains 

 which proves to be a basic ceric chromate. In connection with 

 a study of the methods of separating the cerium earths, begun 

 last summer, we had occasion to make an experiment similar to 

 that described by Bohm, differing possibly in this respect, that 

 we used a decided excess of the chromic acid (100 grms. of the 

 oxides with 150 grms. of chromic acid and 200 cm3 of water). 



The product which we obtained was a bright scarlet crystal- 

 line salt, which, when washed sparingly with water and dried 

 over sulphuric acid, became a little darker in color but retained 

 its crystalline condition. Examined under the microscope the 

 salt appeared homogeneous, and the crystalline form ortho- 

 rhombic, the prevailing habit being prismatic, m /\ m/", 110 ^ 

 110, being approximately 58° C. The macropinacoid, a (100), 

 is generally present, the brachypinacoid, h (010), is well devel- 

 oped, and a flat brachydome and the basal plane, c (001), are the 

 terminating forms. The crystals are etched or pitted, are slightly 

 pleochroic, and exhibit parallel extinction and low birefringence. 

 When treated with water the salt loses chromic acid and 

 becomes an orange yellow. It may be heated to about 150° C. 

 without loss of weight. Between 150° and 180° C. it loses 

 water and becomes brownish red, still retaining much the same 

 original exterior form. Above 180° C. it decomposes. It is 

 quite readily soluble in dilute acids, especially sulphuric acid, 

 and is easily decomposed by potassium or sodium hydroxide 

 into the alkali chromate and ceric hydroxide. The ceric 

 hydroxide thus formed is quite readily soluble in acids and 

 promises to be a convenient starting point for the preparation 

 of ceric salts. Qualitative tests proved the absence of both 

 yttrium and didymium. 



Analysis of the salt gave the following results: Five closely 

 agreeing determinations of water, six determinations of ceric 

 oxide, among which the greatest variation was about one per 

 cent, and sixteen determinations of chromic acid showing as 

 the greatest variation about two per cent, gave the averages 

 tabulated below: 



* Zeitschr. angew. Chem., xv, 1282. 



