Chemistry and Physics. 269 
character. Jt is not improbable that the density of the current required 
to produce a particular chemical decomposition will serve as an accu- 
rate and available measure of the force of chemical affinity under vari- 
ous circumstances of temperature, mass and pressuré.—w. G. 
_ 3. On the losses of weight which minerals undergo by heat.—H. Sr. 
Ciaire Devine and Fouqus have communicated to the Academy of 
Sciences a memoir on this subject containing results which if confirmed 
will prove of much importance for mineral chemistry. The losses of 
perature at which the water is expelled from a mineral lies far below 
that at which the fluorine begins to volatilize. ‘They employ therefore 
two lamps, one fed with a mixture of alcohol and oil of turpentine, the 
= blast: lamp in which the vapors of oil of turpentine are con- 
orine ; the latter completely drives off the fluorine. The nature of the 
of weight which a mineral containing fluorine undergoes depends 
upon its constitution. The authors prepared a basic silicate of soda, 
and fused it over the large lamp, with a weighed portion of pure fluorid 
of calcium. In this case the whole of the fluorine was yolatilized as 
fluorid. of sodium, while a silicate of lime remained, containing the 
Whole of the silica. A second experiment was made with topaz: this 
a 
combination of inverted concentric platinum crucibles, the intervening 
Spaces being filled with lime. This system lost no weight on ignition 
se analyses in which lithium and fluorine have both been determined 
after 'gnition.— Compt. Rend., xxxviii, 317. Ww. G. 
4. Mustrations of Chemical Homology.—Under this title Mr. T. 
Sterny Hunt f iati 
and base, as mnembers of a homologous series. Thus the three nitrates 
Of lead inthe ordinary notation “i PbO, NOs ; HO, 2PbO, NOs; and 
