employed in these earlier experiments was about fifteen grms., about six grms. of hydrogen potassium fluoride, HF.KF, being added in order to render it a conductor.  Since the publication of that memoir a much larger apparatus has been constructed, in order to obtain the gas in greater quantity for the study of its reactions, and important additions have been made, by means of which the fluorine is delivered in a pure state, free from admixed vapor of the very volatile hydrofluoric acid.  As much as a hundred cubic centimeters of hydrofluoric acid, together with twenty grms. of the dissolved double fluoride, are submitted to electrolysis in this new apparatus, and upward of four liters of pure fluorine is delivered by it per hour.

This improved form of the apparatus is shown in the accompanying figure (Fig. 1), which is reproduced from the memoir of M. Moissan.  It consists essentially of two parts—­the electrolysis apparatus and the purifying vessels.  The electrolysis apparatus, a sectional view of which is given in Fig. 2, is similar in form to that described in the paper of 1887, but much larger.

The U-tube of platinum has a capacity of 160 c.c.  It is fitted with two lateral delivery tubes of platinum, as in the earlier form, and with stoppers of fluorspar, F, inserted in cylinders of platinum, p, carrying screw threads, which engage with similar threads upon the interior surfaces of the limbs of the U-tube.  A key of brass, E, serves to screw or unscrew the stoppers, and between the flange of each stopper and the top of each branch of the U-tube a ring of lead is compressed, by which means hermetic closing is effected.  These fluorspar stoppers, which are covered with a coating of gum lac during the electrolysis, carry the electrode rods, t, which are thus perfectly insulated.  M. Moissan now employs electrodes of pure platinum instead of irido-platinum, and the interior end of each is thickened into a club shape in order the longer to withstand corrosion.  The apparatus is immersed during the electrolysis in a bath of liquid methyl chloride, maintained in tranquil ebullition at -23 deg..  In order to preserve the methyl chloride as long as possible, the cylinder containing it is placed in an outer glass cylinder containing fragments of calcium chloride; by this means it is surrounded with a layer of dry air, a bad conductor of heat.

The purifying vessels are three in number.  The first consists of a platinum spiral worm-tube of about 40 c.c. capacity, immersed also in a bath of liquid methyl chloride, maintained at as low a temperature as possible, about -50 deg..  As hydrofluoric acid boils at 19.5 deg.  (Moissan), almost the whole of the vapor of this substance which is carried away in the stream of issuing fluorine is condensed and retained at the bottom of the worm.  To remove the last traces of hydrofluoric acid, advantage is taken of the fact that fused sodium fluoride combines with the free acid with great energy to form the double