CUPROUS CHLORID
I 2
3
1
1.580 1
4
0.212
8
0.139
1
IO
,
0.132 1 2 1 0.132 0.137 14 0.133 0.136 [ I6 0.129
1
1
20
0.139
30 34
0.011 0.000
Lescoeur offers no explanation of these rather curious results but it seems as if there could be no doubt about the cause of the phenomenon. T h e system contains three components and as soon as cuprous oxid is formed there are four phases, cuprous chlorid and oxid, solution and vapor. At a given temperature there can only be one concentration-in this case n/27o-for which the system is in equilibrium. As long as there is an excess of hydrochloric acid there will be no cuprous oxid and the system will be a divariant one, capable of existing' at different concentrations for a given temperature. This is exactly what Lescoeur found. This seemed to be such an interesting case of equilibrium that I repeated the measurements in a thermostat so as to be certain that the temperature did not vary. I placed some freshly precipitated cuprous chlorid in I A ~ chim. . phys. (7) a, 97 (1894).
J. K. Naywood
412
a flask containing water. T h e bottle was carefully stoppered and placed in a thermostat kept at 30'. At the end of about twenty minutes most of the solution was poured off and ten cubic centimeters were titrated with caustic potash. T h e flask was filled with water and replaced in the thermostat and the same series of operations was repeated half a dozen times. T h e results are given in Table 11. T h e values given are the number of cubic Centimeters of a one-hundredth normal caustic potash solution necessary to neutralize ten cubic centimeters of the hydrochloric acid solution.
TABLEI1 (1)
(2)
42.13 8.75
(3) (4)
8-73 (5) 8.78 (6)
II.0
(7)
12
13.1
(8)
11
In the first measurement there was an excess of hydrochloric acid and no cuprous oxid so that the difference between the first and the second measurement is normal. Measurements 2-8 do not agree among themselves as they should. Thinking that the system might not have reached equilibrium, I let another lot stand an hour and a half and found that 10.7 C.C. KOH were necessary to neutralize the acid. I then made measurements every fifteen minutes pipetting off ten cubic centimeters without refilling the flask. T h e readings thus obtained were 14.7, 20.8, 2 7 . 2 , 35.8, 45.2, 57.4 C.C. showing that equilibrium had not been reached. I then made measurements at intervals of forty minutes exactly, decanting the whole of the solution as far as possible and refilling the flask with water. T h e readings were now 9.6, 9.3, 9 . 2 , 9.3, 9.5 C.C. showing that it was possible to get constant values when the time-intervals and the relative masses of the reacting substances do not vary. I t seems very certain froin my measurements that Lescoeur's results were purely accidental and due to his having consciously or unconsciously used always about the same amount of wash-water and having 6madehis measurements with surprising regularity. Since the measurements do not refer to a system of equilibrium, it was to be expected that the relative masses of the different phases would have an effect. I n order to test this I took three flasks, A , B and C, with approximately the same amount of cuprous chlorid in each but with 60, 30 and 15 C.C. of water respectively. Making
Cuprous ChZorid
413
determinations every fifteen minutes and changing the water between each reading, I obtained the results which are given in Table 111.
TABLEI11 A
B
C
6.3 6. I
6.8 6.3
14.1
5.5
6.0
13.9
13.7
6.5 T h e reaction velocity changes very rapidly as we pass from fifteen to thirty cubic centinieters of water and then seems to change very little, if at all. I made one attempt to determine the equilibrium concentration when cuprous chlorid and cuprous oxid are present as solid phases ; but the result was not satisfactory owing to the action of the air dissolved in the water on the cuprous chlorid and the extraordinary length of time necessary to reach equilibrium. 6.0
Cornell University :January, r896.
