Note 16 — Chapter X · SODIUM CHLORIDE—BERTHOLLET'S LAWS—HYDROCHLORIC ACID

Notwithstanding the great simplicity (Chapter I., Note 49) of the observations on the formation of ice from solution, still even for sodium chloride they cannot yet be considered as sufficiently harmonious. According to Blagden and Raoult, the temperature of the formation of ice from a solution containing c grams of salt per 100 grams of water = -0·6c to c = 10, according to Rosetti = -0·649c to c = 8·7, according to De Coppet (to c = 10) = -0·55c - 0·006c2, according to Karsten (to c = 10) - 0·762c + 0·0084c2, and according to Guthrie a much lower figure. By taking Rosetti's figure and applying the rule given in Chapter I., Note 49 we obtain—

i = 0·649 × 58·5 / 18·5 = 2·05.

Pickering (1893) gives for c = 1 - 0·603, for c = 2 - 1·220; that is (c up to 2·7) about - (0·600 + 0·005c)c.

The data for strong solutions are not less contradictory. Thus with 20 p.c. of salt, ice is formed at -14·4° according to Karsten, -17° according to Guthrie, -17·6° according to De Coppet. Rüdorff states that for strong solutions the temperature of the formation of ice descends in proportion to the contents of the compound, NaCl,2H₂O (per 100 grams of water) by 0°·342 per 1 gram of salt, and De Coppet shows that there is no proportionality, in a strict sense, for either a percentage of NaCl or of NaCl,2H₂O.