H. B. Higgs — Separation of Chromium from Iron, etc. 409 



tive proof that it is not an original chemical sediment, while 

 it may in part be from both sources." This statement is made 

 to apply with equal force to the other chert-bearing member of 

 the series.* 



Regarding the Lower Magnesian and Lower Carboniferous 

 cherts from southern and southwestern Missouri, the present 

 writer's conclusion is, that they are due to chemical precipita- 

 tion, probably at the time of the deposition of the strata in 

 which they occur or before their consolidation. 



Am. Mus. Nat. Hist., N. Y. City, July, 1894. 



Art. LYIII. — The Qualitative Separation of Chromium from 

 Iron and Aluminium / by R. B. RiGrGS.f 



The separation of chromium from iron and aluminium 

 depends on the conversion of chromium compounds, by oxida- 

 tion, into soluble chromates. This oxidation is generally 

 effected, either by fusing the hydroxide or basic acetate pre- 

 cipitates with sodium carbonate and potassium nitrate, or by 

 dissolving them in concentrated nitric acid to which potassium 

 chlorate has been added. In the hands of the general student 

 the latter is probably the more satisfactory of the two methods. 

 It is somewhat complicated however, involving, as it does, the 

 separation of the aluminium by means of potassium hydroxide, 

 solution of the residue in a potassium chlorate-nitric acid solu- 

 tion, and a reprecipitation of the iron. 



In many cases the efficiency of hydrogen peroxide, in alka- 

 line solutions, as an oxidizing agent, is well known. Its use in 

 converting chromium hydroxide into the chromate was a natu- 

 ral suggestion. A few experiments showed that, under favor- 

 ing conditions, this change is easily and completely brought 

 about. Solutions, containing the equivalent of O05 grm. of 

 chromium as hydroxide, 0*3 grm. of sodium hydroxide and 

 quantities of hydrogen peroxide (15 per cent) varying from 5 

 to 20 C • OI, •, varying in volume from 50 to 500 cc8- , were digested 



* lb., pp. 397 and 368. 



f Since writing this note my attention has been called to an article by Clark 

 (Jour. Chem. Soc, 1893, i, 1079), on ''The use of Sodium peroxide as an Ana- 

 lytical agent." He makes very successful use of this reagent in decomposing 

 ferro chromium ores, and says that it may be used for the qualitative separation 

 of chromium from iron and manganese, in alkaline solutions, when it acts quickly 

 even in the cold. As compared with hydrogen peroxide, sodium peroxide is the 

 more powerful oxidant, and if the former has any advantage, it is to be found in 

 convenience and, possibly, economy. 



