12 ELECTROCHEMICAL INVESTIGATION OF LIQUID AMALGAMS 



DENSITIES OF THE AMALGAMS. 



It has been pointed out K that a knowledge of the densities of the various 

 amalgams is essential in order to fix accurately the value of the concen- 

 tration-ratio in calculating the theoretical potentials of the cells. More- 

 over, such data make possible the calculation of the contraction or expan- 

 sion occurring on the amalgamation of the various metals. For these 

 reasons numerous determinations were made of the densities of the amal- 

 gams of thallium, indium, and tin. 



The pycnometer used was of the Sprengel type, as modified by Ostwald ; 

 its capacity was about 3 cc. and its tubes I mm. in diameter. Before use it 

 was thoroughly cleaned with appropriate reagents, and, after washing with 

 water, dried by suction. The weight of the pycnometer filled with mercury 

 at 20 was then carefully determined. Since in filling the pycnometer 

 with the amalgams, it was sometimes difficult to adjust the contents exactly 

 to the marks, the weight of a centimeter length of mercury in the capillary 

 was determined, and a suitable correction was applied. The length of any 

 excess in the column of amalgam was accurately determined with dividers. 

 Since the correction was small, never amounting to more than 0.15 gram, 

 the difference in density between mercury and the amalgam would cause 

 no appreciable error. All the densities were determined at 20. The 

 amalgams used in these determinations were prepared in the manner 

 already described. When all was ready, a sufficient quantity of the 

 amalgam was run out into a small weighing bottle, filled with carbon 

 dioxide, and hastily drawn up into the pycnometer. By working in this 

 fashion, no serious oxidation occurred. The thread of mercury was 

 adjusted only after the pycnometer had been in a thermostat at 20.0 for 

 some time. 



The data of a typical determination are as follows : 



Weight of pycnometer and 



mercury 53.228 



Weight of pycnometer alone.... 18.134 



Weight of mercury 3S-OQ4 



Weight of pycnometer and amal- 

 gam 53.121 



Weight of pycnometer alone.... 18.134 



Weight of amalgam 34.987 



The density of mercury at 20 is 13.545, therefore the density of the 

 amalgam is 



3_4j9__Z x 13.545 = I 3-54 

 35-094 



This amalgam contained 1.845 P er cent thallium. 



Table I contains the results with amalgams of thallium, indium, and tin. 

 There are given also imaginary values which the densities would have 

 shown if no contraction or expansion had taken place on amalgamation. 



25 Richards and Forbes, Publication of Carnegie Institution of Washington, No. 

 56, II (1906). Also, pp. 6 and 7 of the present monograph. 



