oughly oxidized by reversing the current every few minutes. To reverse the current use the contrivance C; this is nothing more than a square block of wood fastened to the top of the table 7, by a screw or nail. The four depressions (x) in it contain a few drops of mercury, into which the side binding screws (a) project. The mercury cups are made to communicate with each other by a cap of wood, D, carrying two metallic wires, which pass through it and project a slight distance on its lower side. By raising the cap and turning it so that the wires are vertical (1) or horizontal (→), the crucible or the platinum wire extending into the fused mass can be made the anode or cathode in a few seconds. E is a Kohlrausch amperemeter (Fig. 15), and R the resistance frame (Fig. 13).

Storage batteries furnish the most satisfactory current for work of this character. In the sketch the cells stand beneath the table; the wire from the anode passes through a hole in the table top, and is attached to one of the binding posts of the block C, while the positive wire is attached to a binding post at the end of the table top, and from here it passes to the resistance frame R, where it is fixed by an ordinary metallic clamp.

For most purposes the strength of current need not exceed 1-1.5 amperes per minute; however, it may be necessary occasionally to increase it to 4 amperes per minute. Pyrite, FeS2, is even then not completely

decomposed. This particular case requires the addition of a quantity of cupric oxide equal in weight to the pyrite, and a current of the strength last indicated before all of its sulphur is fully converted into sulphuric acid.

By increasing the number of crucibles it will be possible to conduct at least from four to six of these decompositions simultaneously, and by using a volumetric method for estimating the sulphuric acid, a sulphur determination can easily be executed in forty minutes.

Experience has demonstrated that 0.1-0.2 gram of material will require about 20-25 grams of caustic potash.

The arsenic in minerals is rapidly oxidized to arsenic acid by this method.

Chromite also seems to be rapidly decomposed when subjected to this treatment. Several quantitative experiments have been carried out, and the results obtained were very satisfactory.