4 TRANSACTIONS OF THE [oor Le 
inhaling and exhaling the gas. Some small crystals of silicon 
were placed in the open end of the tube, and when the closed end 
of the tube was heated the silicon burnt with vivid incandes- 
cence and even with explosive violence (Moissan’s test for fluor- 
ine). The residue is white or slightly yellow but care must be 
taken to exclude moisture, for when water vapour comes into 
contact with the heated salt, hardly any fiuorine is given off, 
and a brown deliquescent residue is left. 
This experiment has been repeated several times, and it con- 
firms the accuracy of the results obtained by me 13 years ago, 
viz.: that fluorine may be obtained on heating some higher 
fluorides. Although Moissan has since then obtained free 
fluorine by a physical method, we have here the first trust- 
worthy chemical process of obtaining this gas. If potassium 
fluoplumbate loses its hydrogen fluoride at about 230° without 
losing more than traces of fluorine, one gram of the salt should 
yield on heating 47 c¢. c. of fluorine which could be freed from 
any hydrogen fluoride present by passing it over potassium 
fluoride, according to Moissan. 
Qualitative experiments have shown that a whole series of 
fluoplumbates exist, the metals forming them being the same 
as those in Marignac’s series of fluostannates, but unfortun- 
ately the work is connected with great experimental difficulties, 
for some of the salts are decomposed by moisture as soon as. 
they are taken out of the mother liquor. 
FLUOPLUMBIC ACID AND LEAD TETRAFLUORIDE. 
Fluoplumbic acid is obtained either on dissolving some forms 
of hydrated lead dioxide in hydrofluoric acid or on dissolving 
lead tetra-acetate in strong hydrofluoric acid, acetic acid being 
liberated in this case, for on adding soluble fluorides to this 
solution it gives the corresponding fluoplumbates. This solu- 
tion, however, cannot be evaporated to dryness, even at the 
ordinary temperature, a crust of the brown lead dioxide being 
deposited. 
In order to prepare anhydrous lead tetrafluoride potassium 
fluoplumbate was reduced to a fine powder in a platinum basin, 
using a small platinum crucible as a pestle; a dry agate mortar 
cannot be used, for in contact with silica the salt gives silicon 
tetrafloride, water being formed which at once decomposes the 
salt. The powdered salt (0.874 grm.) was then thrown on the 
surface of cold, concentrated sulphuric acid (5 ce.). Hydrogen 
fluoride at once escapes and a pale yellow solution is obtained, 
having the same characteristic color as that of lead tetrachlo- 
