oride when heated to low redness, and at a
slightly higher temperature the fluoride is dissociated into metallic
gold and fluorine gas.

The action of fluorine on _platinum_ has been studied with special
care. It is evident, in view of the corrosion of the positive platinum
terminal of the electrolysis apparatus, that nascent fluorine rapidly
attacks platinum at a temperature of -23 deg.. At 100 deg., however, fluorine
gas appears to be without action on platinum. At 500 deg.-600 deg. it is
attacked strongly, with formation of the tetrafluoride. PtF_{4}, and a
small quantity of the protofluoride, PtF_{2}. If the fluorine is
admixed with vapor of hydrofluoric acid, the reaction is much more
vigorous, as if a fluorhydrate of the tetrafluoride, perhaps
2HF.PtF_{4}, were formed. The tetrafluoride is generally found in the
form of deep-red fused masses, or small yellow crystals resembling
those of anhydrous platinum chloride. The salt is volatile and very
hygroscopic. Its behavior with water is peculiar. With a small
quantity of water a brownish yellow solution is formed, which,
however, in a very short time becomes warm and the fluoride
decomposes; platinic hydrate is precipitated, and free hydrofluoric
acid remains in solution. If the quantity of water is greater, the
solution may be preserved for some minutes without decomposition. If
the liquid is boiled, it decomposes instantly. At a red heat platinic
fluoride decomposes into metallic platinum and fluorine, which is
evolved in the free state. This reaction can therefore be employed as
a ready means of preparing fluorine, the fluoride only requiring to be
heated rapidly to redness in a platinum tube closed at one end, when
crystallized silicon held at the open end will be found to immediately
take fire in the escaping fluorine. The best mode of obtaining the
fluoride of platinum for this purpose is to heat a bundle of platinum
wires to low redness in the fluorspar reaction tube in a rapid stream
of fluorine. As soon as sufficient fluoride is formed on the wires,
they are transferred to a well stoppered dry glass tube, until
required for the preparation of fluorine.

ACTION OF FLUORINE UPON NON-METALLIC COMPOUNDS.

_Sulphureted Hydrogen._--When the horizontal tube shown in Fig. 3 is
filled with sulphureted hydrogen gas and fluorine is allowed to enter,
a blue flame is observed on looking through the fluorspar windows
playing around the spot where the fluorine is bein