ARSENIC. 
§ 775-] 
The inner electrode forming the cathode is a cone of sheet platinum 
provided with several perforations. It is suspended from a hook made 
on the end of the wire passing through the glass stopper, and is adjusted 
so that when the stopper is inserted in the vessel the lower edge of the 
electrode is one millimetre above the bottom of the vessel; it is then 
securely attached to the wire by closing the hook. The porous vessel 
is two or three times larger in diameter than the cylindrical portion of 
the glass vessel. The glass vessel rests by its bulged-out shoulder on 
the edge of the porous vessel, and is thus kept off the bottom. 
The porous vessel is of unglazed, highly siliceous ware. The cell for 
the anode consists of a stout glass vessel, upon the flat bottom of which 
the porous vessel supporting the bulged glass vessel stands. The 
anode consists of a band of platinum 2 cm. broad, passing loosely 
round the porous cell and connected with the current by means of a 
stout platinum wire. The apparatus, lastly, is put in a large dish con¬ 
taining cold water, for, in action, the temperature should not exceed 
50° C. The drying tube is prepared by inserting, first, cotton-wool, and 
then granulated calcium chloride for about 5 cm. ; another loose plug 
of cotton-wool follows, then a roll of dried lead acetate paper. To the 
end of the drying tube is fixed, by means of rubber, a hard Jena glass 
tube, outside diameter 5 mm., inside 3-5 mm. ; a portion of this tube, 
2 cm. in length, 5 cm. from the end of the tube, is drawn out to a length 
of 7-8 cm., having at a distance of 1 cm. from the shoulder of the tube 
an external diameter of 2 mm., a size to be maintained as nearly as 
possible throughout the length of the constricted part. 
The tube is drawn out, cut off near the end of the drawn-out portion, 
and the last cm. turned up at right angles. 
A piece of platinum gauze 2 cm. square is wrapped round the hard 
glass tube at the point where it is to be heated by a Bunsen flame. A 
special small burner is recommended with slotted cone to receive the 
tube. The current giving the best results is one of five amperes and 
seven volts ; this may be obtained in places where there is a continuous 
supply of electricity from the mains by interposing suitable resistances, 
such, for instance, as a rheostat of incandescent lamps. 
The authors have used for some time a boron battery of four cells, 
the exciting liquid being a sulphuric acid solution of potassic bichromate ; 
the amperage and voltage are regulated by a sliding resistance. 
The method of working is as follows :—After thoroughly cleansing 
and connecting up, 30 c.c. of dilute sulphuric acid (1:7) are poured 
into the anode cell and 20 c.c. into the cathode cell by means of the 
stoppered bottle, the stem of which must be kept full of liquid. 
The current is allowed to pass for about ten minutes to expel air, 
and. then the burner is lighted so as to heat the hard glass tube, and 
the current passed for another fifteen minutes ; if by the end of this 
