Note 13 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE

In the formation of steam (from one part by weight [1 gram] of hydrogen) 29,000 heat units are evolved. The following are the quantities of heat (thousands of units) evolved in the formation of various other corresponding compounds of oxygen and of chlorine (from Thomsen's, and, for Na2O, Beketoff's results):

2NaCl, 195; CaCl₂, 170; HgCl₂, 63; 2AgCl, 59.

Na₂O, 100; CaO, 131; HgO, 42; Ag₂O, 6.

2AsCl₃, 143; 2PbCl₅, 210; CCl₄, 21; 2HCl, 44 (gas).

As₂O₃, 155; P₂O₅, 370; CO₂, 97; H₂O, 58 (gas).

With the first four elements the formation of the chlorine compound gives the most heat, and with the four following the formation of the oxygen compound evolves the greater amount of heat. The first four chlorides are true salts formed from HCl and the oxide, whilst the remainder have other properties, as is seen from the fact that they are not formed from hydrochloric acid and the oxide, but give hydrochloric acid with water.