OF ARTS AND SCIENCES. 89 



was also noticed by Donath, a comparatively large amount of the 

 sesquioxide of chromium. 



Another serious difficulty was met with later in the process ; namely, 

 in determining the exact point where sufficient ferrous sulphate had 

 been added to reduce the excess of permanganate of potassium, used 

 in oxidizinsf the small amount of reduced chromic acid. The chancje 

 of color of the solution being so slight as to be almost useless as an 

 indicator. 



We were therefore unable, with the most careful manipulation, to 

 obtain satisfactory results with the above process. In our study of the 

 process we made a great many experiments with different fusing mix- 

 tures, and also tried various ways of oxidizhig the small amount of 

 sesquioxide of chromium we always found present in the solution. The 

 result of these experiments have enabled us to formulate a very quick 

 and simple process, which, as can be seen by the results given below, 

 is also, as regards accuracy, very satisfactory. 



About three tenths of the very finely divided mineral is mixed with 

 twenty times its weight of a mixture containing equal parts of dry 

 sodium carbonate and barium dioxide, and heated in a platinum cru- 

 cible with the full flame of one Bunsen lamp for one half-hour. At 

 the end of this time a quiet fusion is obtained and the decomposition 

 is completed. The crucible is then placed in a beaker, covered with 

 water, and hydrochloric acid added, a little at a time, till the mass is 

 completely disintegrated. The crucible is then removed, the solution 

 made strongly alkaline with caustic potash, and five or six cubic centi- 

 meters of a five per cent solution of hydrogen dioxide added to 

 oxidize the small amount of reduced chromic acid that may be present. 

 The solution is now boiled for twenty minutes to remove any excess of 

 hydrogen dioxide, made acid with hydrochloric acid, and the amount 

 of chromic acid determined by the aid of a standardized solution of 

 ferrous chloride. 



Six analyses of a sample of chrome iron gave the following per 

 cents of chromium sesquioxide. 



1. 2. 3. 4. 5. 6. 



49.87 49.97 49.84 49.85 49.88 49.87 



The solution of ferrous chloride used was kept under oil and titrated 

 before each analysis. One cubic centimeter equalled about 0.015 

 gram of chromium sesquioxide. 



Salisbury Labokatories, 



Worcester Polytechnic' Institute. 



