Note 38 — Chapter X · SODIUM CHLORIDE—BERTHOLLET'S LAWS—HYDROCHLORIC ACID
George Kamensky translation
According to Roscoe at 0° one hundred grams of water at a pressure p (in millimetres of mercury) dissolves—
p = 100 200 300 500 700 1000
Grams HCl 65·7 70·7 73·8 78·2 81·7 85·6
At a pressure of 760 millimetres and temperature t, one hundred grams of water dissolves
t = 0 8° 16° 24° 40° 60°
Grams HCl 82·5 78·3 74·2 70·0 63·3 56·1
Roozeboom (1886) showed that at t° solutions containing c grams of hydrogen chloride per 100 grams of water may (with the variation of the pressure p) be formed together with the crystallo-hydrate HCl,2H2O:
t = -28°·8 -21° -19° -18°
c = 84·2 86·8 92·6 98·4 101·4
p = — 334 580 900 1,073 mm.
The last combination answers to the melted crystallo-hydrate HCl,2H2O, which splits up at temperatures above -17°·7, and at a constant atmospheric pressure when there are no crystals—
t = -24° -21° -18° -10° -0°
c = 101·2 98·3 95·7 89·8 84·2
From these data it is seen that the hydrate HCl,2H2O can exist in a liquid state, which is not the case for the hydrates of carbonic and sulphurous anhydrides, chlorine, &c.
According to Marignac, the specific heat c of a solution HCl + mH2O (at about 30°, taking the specific heat of water = 1) is given by the expression—
C(36·5 + m18) = 18m - 28·39 + 140/m - 268/m2
if m be not less than 6·25. For example, for HCl + 25H2O, C = 0·877.
According to Thomsen's data, the amount of heat Q, expressed in thousands of calories, evolved in the solution of 36·5 grams of gaseous hydrochloric acid in mH2O or 18m grams of water is equal to—
m = 2 4 10 50 400
Q = 11·4 14·3 16·2 17·1 17·3
In these quantities the latent heat of liquefaction is included, which must be taken as 5–9 thousand calories per molecular quantity of hydrogen chloride.
The researches of Scheffer (1888) on the rate of diffusion (in water) of solutions of hydrochloric acid show that the coefficient of diffusion k decreases with the amount of water n, if the composition of the solution is HCl,nH2O at 0°:—
n = 5 6·9 9·8 14 27·1 129·5
k = 2·31 2·08 1·86 1·67 1·52 1·39
It also appears that strong solutions diffuse more rapidly into dilute solutions than into water.