Note 55 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE
George Kamensky translation
For instance, the experiment with Dutch metal foil (Note 16) may be made with bromine just as well as with chlorine. A very instructive experiment on the direct combination of the halogens with metals maybe made by throwing a small piece (a shaving) of aluminium into a vessel containing liquid bromine; the aluminium, being lighter, floats on the bromine, and after a certain time reaction sets in accompanied by the evolution of heat, light, and fumes of bromine. The incandescent piece of metal moves rapidly over the surface of the bromine in which the resultant aluminium bromide dissolves. For the sake of comparison we will proceed to cite several thermochemical data (Thomsen) for analogous actions of (1) chlorine, (2) bromine, and (3) iodine, with respect to metals; the halogen being expressed by the symbol X, and the plus sign connecting the reacting substances. All the figures are given in thousands of calories, and refer to molecular quantities in grams and to the ordinary temperature:—
1 2 3
K2 + X2 211 191 160
Na2 + X2 195 172 138
Ag2 + X2 59 45 28
Hg2 + X2 83 68 48
Hg + X2 63 51 34
Ca + X2 170 141 —
Ba + X2 195 170 —
Zn + X2 97 76 49
Pb + X2 83 64 40
Al + X2 161 120 70
We may remark that the latent heat of vaporisation of the molecular weight Br2 is about 7·2, and of iodine 6·0 thousand heat units, whilst the latent heat of fusion of Br2 is about 0·3, and of I2 about 3·0 thousand heat units. From this it is evident that the difference between the amounts of heat evolved does not depend on the difference in physical state. For instance, the vapour of iodine in combining with Zn to form ZnI2 would give 48 + 8 + 3, or about sixty thousand heat units, or 1½ times less than Zn + Cl2.