to effect the reduction of the carbonate of calcium into caustic lime.  It is only necessary then to expose the loaves to the air at the ordinary temperature, for the oxidation of the sesquioxide of chromium will go on by degrees without any manipulation, by the action of the atmospheric air, the matter thus prepared having a sufficient porosity to allow the air free access to the interior of the mass.  Under ordinary conditions the oxidation will be completed in a month.  The division of this work—­mixing, slaking or thinning, roasting or baking, and subjection to the air—­is analogous to the work of a tile or brick works.  The advance of the oxidation can be followed by the appearance of the matter, which after baking presents a deep green color, which passes from olive green into yellow, according to the progress of calcium chromate formation.  When the oxidation is completed, the mass contains:  Chromate of calcium, chloride of calcium, carbonate of lime and caustic lime in excess, sesquioxide of iron and the gangue, part of which is united with the lime.  This mass is washed with water by the ordinary method of lixiviation, and there is obtained a concentrated solution containing all the chloride of calcium, and a small quantity only of chromate of calcium, the latter being about 100 times less soluble in water.

This solution can be used in the following ways: 

1.  It can be concentrated and used in preparing a new charge, the small quantity of calcium chromate present being an assistance, or: 

2.  It can be used for making chromate of lead (chrome yellow), by precipitating the calcium chromate with a lead salt; this being a very economical process for the manufacture of this color.

The mass after lixiviation, being treated with a solution of sulphate or carbonate of potash or soda, will yield chromate of potash or soda, and by the employment of sulphuric acid, the corresponding bichromates.  The solutions are then filtered, to get rid of the insoluble deposits, concentrated, and crystallized.

If, instead of chromate or bichromate of potash or soda, chromic acid is sought, the mass after lixiviation is treated with sulphuric acid, and the chromic acid is obtained directly without any intermediate steps.

This process has the following advantages: 

1.  The oxidation can be effected at the ordinary temperature, thus saving expense in fuel.

2.  The heavy manual labor is avoided.

3.  The loss of potash and soda by volatilization and combination with the gangue is entirely avoided.

4.  It is not actually necessary to use rich ores; silicious ores can be used.

5.  The intimate mixture of the material before treatment being made mechanically, the puddling is avoided, and in consequence a greater proportion of the sesquioxide of chromium in the ores is utilized.—­Bull.  Soc.  Chem. 5, 371.

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