348 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The method employed was to treat calomel with solutions of chlorides 

 of various concentrations for varying times, and to determine the extent 

 of the reaction by determining the amount of mercury dissolved. 



Preparation of Materials. 



Mercury already very pure was thoroughly freed from the possible 

 presence of substances with greater solution-tension by treatment with 

 sulphuric acid and potassic dichromate, and subsequent spraying through 

 ten per cent nitric acid. Calomel was resublimed at as low a temperature 

 as possible, and thoroughly washed with water and with the solution to 

 be used in each particular case. One of us had previously shown that 

 the source of the calomel is immaterial.* Sodic chloride was precipitated 

 by pure hydrochloric acid from a saturated solution of the so-called 

 " chemically pure " salt. It was then twice recrystallized from water, 

 and thoroughly dried to drive off any possible traces of acid. Pure 

 calcic nitrate was made by many recrystallizations ; this was converted 

 into carbonate, and the carbonate converted again into chloride. Several 

 recrystallizations freed this chloride from every trace of the nitrate or of 

 ionized hydrogen. Baric chloride was crystallized first from a solution 

 strongly acid with hydrochloric acid, and subsequently from aqueous 

 solutions by precipitation with pure alcohol. It also was wholly neutral 

 to methyl orange. Cadmic chloride was made by dissolving the pure 

 metal in pure acid and recrystallizing twice. The salt was dried 

 thoroughly in order to make certain of the absence of ionized hydrogen, 

 which is less easily detected in this case. Hydrochloric acid itself was 

 purified by redistillation, the purest acid of commerce serving as the 

 starting-point. 



Apparatus and Method of Analysis. 



It was necessary to digest the mixtures for long periods of time 

 at a constant temperature. For this purpose they were placed in large 

 test-tubes of sixty cubic centimeters capacity arranged to rotate tran- 

 sit-fashion in an Ostwald thermostat after the manner suggested by 

 Schroder. f In the case of the weaker solutions several of these tubefuls 

 were used for each analysis, but with the stronger solutions fifty cubic 

 centimeters sufficed. The tubes were corked with rubber stoppers 



* Richards, loc. cit. 



t Richards and Faber, Am. Ch. J., 21, 168 (1899). The thermometer used to 

 register the temperature was of course suitably verified. 



