RICHARDS AND ARCHIBALD. — CONCENTRATED SOLUTIONS. 349 



which had previously been boiled with dilute alkali and scrupulously 

 rubbed and waslied. Into each tube was placed a large excess of 

 calomel, about a decigram of mercury, and fifty cubic centimeters of one 

 of the solutions of chlorides. 



After a slight shaking, the settled precipitate was always covered 

 upon standing with a layer of gray partially reduced material, which 

 settled more slowly and hence gave more opportunity for reduction. 

 Wheu the equilibrium was completed by prolonged shaking, this gray 

 material was mixed evenly throughout, and no longer appeared on the 

 surface of the precipitate. Thus the absence of a gray film on settling 

 was a rough guide to the completion of the reaction. 



After five or six hours of agitation in the thermostat at 25.° ± 0.05° 

 one of the tubes was opened, its contents filtered, and the dissolved mer- 

 cury determined analytically. At intervals of an hour successive tubes 

 were similarly treated, and after seven or eight hours no change was 

 found in any case. Evidently a state of equilibrium is soon attained, 

 and the reaction cannot be called catalytic. The values giveu below are 

 of course the values corresponding to this maximum. 



In this paper no evidence is given concerning the size of the grains of 

 calomel. Ostwald * has recently shown that this may be an important 

 factor in determining the concentration of a saturated solution, and 

 hence in fixing the basis of the present equilibrium. Concerning this 

 point it need only be said that while the absolute extent of solubility 

 may vary with the size of the grains, the relative results, upon which 

 alone the conclusions of this paper are founded, are not affected. This is 

 the case because the same preparation of calomel was used in every 

 instance. Moreover, since the calomel was sublimed and since it is 

 notoriously difficult to powder, the individual diameters could not have 

 been very small, hence a value approximating that corresponding to a 

 flat surface must have been obtained. 



A number of experiments indicated that the mercury salt thus dis- 

 solved was in the mercuric rather than in the mercurous state. The 

 visible deposition of mercury during the reaction is alone almost enough 

 to prove this. Moreover, neither permanganate nor bichromate suffered 

 more than the faintest trace of reduction upon addition to a solution 

 which contained much dissolved mercury. The minute trace of decolor- 

 ization which was observed was no greater than that produced by a solu- 

 tion of mercurous chloride in pure water. On the other hand, small 



* Zeitschr. phys. Chem., 34, 495 (1900). 



