l6 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



of mercury which had undergone a similar purification. According to 

 Hulett, 39 the resulting product should be very pure. It was then distilled 

 under 20 mm. of hydrogen in an apparatus suggested by Hulett, but improved 

 by the elimination of rubber joints. The hydrogen generator used was simi- 

 lar to the one to be described on page 19. A long tube containing granulated 

 calcium chloride dried the gas before it entered the mercury. All air was 

 replaced by hydrogen as completely as possible before heating the mercury. 



The entire apparatus was one continuous piece of blown glass without a 

 single piece of cork or rubber, as far as the exhaust to the water pump. A 

 stopcock regulating the supply of gas bubbling through the mercury was 

 lubricated with sirupy phosphoric acid. The possibility of leakage of air 

 or the introduction of sulphur compounds was thus eliminated. Great con- 

 fidence was placed in the purity of the product. 



The materials thus described contained no impurities dangerous to the 

 success of the potential measurements. In fact, as there was to be measured 

 only a concentration effect, it seemed highly probable that pure materials of 

 commerce would have done almost as well. A few approximate experi- 

 ments, performed after the work with pure materials was finished, tended to 

 bear out the truth of this supposition. Nevertheless, it was desired to run 

 no risks, and complete purity was therefore sought, as far as possible. 



Water twice distilled in a block-tin condenser was used to prepare all 

 solutions. All vessels used in this part of the research were treated with 

 cleaning solution and well washed with distilled water ; they were dried, 

 when necessary, by successive washings with alcohol and ether ; a current of 

 air was finally sucked through them by a filter pump. The alcohol and ether 

 were freed from water by lime and calcium chloride, respectively. They were 

 distilled from a glass-stoppered flask because cork or rubber pollute the dis- 

 tillate. The delivery tube of the flask was inserted far into the condenser, 

 and a light packing of Swedish filter paper discouraged convection currents. 

 The products left no residue on glass, and could therefore be safely used for 

 drying purposes. 



An important material was the rubber lubricant, which came into contact 

 with the pure amalgams and solutions during many operations of the 

 research. Pure gum rubber was dissolved in its own weight of hard paraffin 

 by rubbing the heated mixture with a pestle. Sufficient soft paraffin was 

 then added to bring the lubricant to the proper consistency. The whole was 

 then strained through a clean cotton cloth. It is difficult to imagine the 

 presence of metals, decomposable sulphur compounds, or acids in the 

 product. 



Zeit. Phys. Chem., 33, 611 (1900). 



