Page:Text-book of Electrochemistry.djvu/310

 XVII. FUSED ELECTROLYTES. sgs

dissociation of water must increase more slowly (in the ratio 12: 14) with rising temperature than does that of carbon dioxide. Most substances (gaaes) on decomposition suffer an increase of volume — the number of molecules, as a rule, is increased by the decomposition — consequently, heat, which alone would not be able to bring about the dissociation, is frequently assisted by the simultaneous volume increase which takes place when the temperature is raised.

From this circumstance it is easy for us to see that in the visible layers of the sun's atmosphere, which possess a very high temperature and a relatively low pressure, the substances are all decomposed into their ultimate elements. The metals, whose presence in the sun has been detected by spectrum analysis, occur there in the form of simple atoms, just as is the case with these substances in solution at the ordinary temperature. In other words, in the sun there ai-e formed as many, and as light, molecales as possible. It may well be, however, that in the interior of the sun, where quite enormous pressure probably obtains, compounds like water am capable of

��Fused Electrolytes. Heroult's Furnace.— For the

preparation of aluminium ITeroult (S) constructed a fur- ■*"

nace which consists essen- tially of a large iron crucible, F, provided with plates of carbon, C (Fig. 50). This is filled with a mixture, B, of two parts of sodium chloride and one part of cryolite (NagAlFfl), which is fused by being heated from below. When the mass has fused, a bundle of carbon rods, ^,13 Fi M

introduced, and this serves 83 anode, the carbon jilates, C, being iised as cathode.

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