. Introduction to inorganic chemistry . , after receiving athin coating of the fluoride, is not furtheraffected. To reduce the tendency to chem-ical union, the whole is immersed in a bathgiving a temperature of — 23°. The elec-trodes are made of an alloy of platinum andiridium, which is the only substance thatcan resist the action of the fluorine whenfreshly liberated by the electric fluoride, like other hydrogenhalides, is a nonconductor of electricity, anda small quantity of potassium fluoride has to be added to enable thecurrent of electricity to pass. The fluorine is set f
. Introduction to inorganic chemistry . , after receiving athin coating of the fluoride, is not furtheraffected. To reduce the tendency to chem-ical union, the whole is immersed in a bathgiving a temperature of — 23°. The elec-trodes are made of an alloy of platinum andiridium, which is the only substance thatcan resist the action of the fluorine whenfreshly liberated by the electric fluoride, like other hydrogenhalides, is a nonconductor of electricity, anda small quantity of potassium fluoride has to be added to enable thecurrent of electricity to pass. The fluorine is set free at the positiveelectrode, and hydrogen appears at the negative. The U-tube is closedafter the introduction of the hydrogen fluoride by means of blocks madeof calcium fluoride, which is naturally unable further to enter into com-bination with fluorine. For the reception and examination of thefluorine gas, other copper tubes can be screwed on to the side necks ofthe apparatus, and, when necessary, small windows of calcium fluoride. Fio. 71. THE HALOGEN FAMILY 241 «caii be provided. It has been found that fluorine dried with extraor-dinary precautions is without action on glass. Physical Properties. — Fluorine is a gas whose color is like thatof chlorine, but somewhat paler. Its density has not been measuredwith great exactitude, but the value obtained indicates a molecularweight of 38, showing that there are two atoms in the molecule (theatomic weight is 19). The gas is the most difficult of the halogens toliquefy. The liquid boils at - 186°. Chemical Properties, — Fluorine unites with every element, withthe exception of oxygen, and in many cases does so with such vigorthat the union begins spontaneously without the assistance of externalheat. Dry platinum and gold are the elements least affected. Itexplodes with hydrogen at the ordinary temperature, without theassistance of sunlight. Fluorine displaces oxygen from water instan-taneously and gives ozone {q-v.). On th
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