1894) NEW YORK ACADEMY OF SCIENCES. 5 
ride, which was isolated by Friedrich in this laboratory. Dense 
fumes soon begin to come off, having an extremely pungent 
smell which resembles that of free fluorine. They seem to 
contain some gaseous lead tetrafluoride. After the salt has 
completely dissolved in the acid: 3K F.HF.PbF,+3H,SO,— 
4HF+3KHSO,+PbF,, the clear yellow liquid begins to get 
turbid, and after half an hour or so it is converted into a thick 
lemon-yellow jelly. From this emulsion, which probably con- 
tains the collodial modification of lead tetrafluoride, the latter 
cannot be separated at the ordinary temperature. On heating 
the mass to 100°, some hydrofluoric acid escapes, and a heavy, 
lemon-yellow powder is deposited on the bottom of the crucible, 
this probably being another modification of lead tetrafluoride. 
The sulphuric acid could be easily poured off from the yellow 
precipitate, and it was found that the acid contains no lead in 
solution. _ 
The yellow powder could be washed with sulphuric acid by 
decantation, and no apparent change took place on heating 
the mixture to 100°. But as soon as it was heated to 115°, 
compléte decomposition took place and white lead sulphate was 
left at the bottom of crucible: PbF,+H,SO,—PbSO,+2HF+ 
F,(?). 
‘ have not yet been able to isolate lead tetrafluoride, in spite 
of numerous attempts, as no liquid could be found which would 
displace the sulphuric acid without at the same time decompos- 
ing the tetrafluoride. Dry plates of plaster of Paris absorb the 
greater part of the acid, but not all, and after some time decom- 
position takes place and the brown dioxide is formed: PbF,+ 
2H,O—PbO,+4HF. Hydrofluoric acid dissolves it partly and 
the solution contains fluoplumbic acid, for it liberates iodine 
from potassium iodide, ete. 
On comparing the properties of the incompletely studied lead 
tetrafluoride with those of lead tetrachloride, which I often had 
an opportunity of observing, as it was discovered by Friedrich 
in this laboratory, it will be seen that both substances are set 
free from their double salts by strong sulphuric acid, without 
being decomposed by it. The tetrachloride is a liquid, whilst 
the tetrafluoride seems to exist in several forms. I hope to be 
able to throw some light on the tetrafluoride of lead by a com- 
parative study of the anhydrous tetrafluoride of tin. 
LEAD DISULPHATE. 
Potassium fluoplumbate was dissolved in a very large excess 
of cold sulphuric acid so that even after several days no separa- 
