THE PROBABLE CAUSES OF THE DEVIATIONS. 63 



from the theoretical coincided with the inference from deviation in the elec- 

 tromotive force, it would be reasonable to suppose that both deviations were 

 due to the same ultimate cause, and that this was the only cause. 



The only results which seem to have been obtained upon this matter are 

 those of Ramsay on the decrease of vapor pressure of mercury at 260 

 caused by the solution of a metal. He found the atomic weight of cadmium 

 in three solutions containing 0.04, 1.08, and 1.92 per cent of cadmium to be 

 100.2, 99.7, and 103.8, respectively. Neglecting the first of these results, 

 because the amalgam was then too dilute for sufficient percentage accuracy, 

 the others give an average atomic weight of 101.8 (instead of the true value 

 1 12.5) for cadmium in an amalgam containing 1.5 per cent of this metal. 

 The osmotic pressure was therefore about 10 per cent too great in this 1.8 

 atomic-normal solution. Such an excess is four times as large as that which 

 would be caused by a " useless space " equal to the volume of the dissolved 

 cadmium, for this amalgam is essentially like amalgam 5 of this paper, which 

 has just been calculated to show a " useless " space of only about 2.5 per 

 cent of the total volume. 



In short, while both Ramsay's results and ours vary from the simplest 

 theory in the same direction, they differ greatly in the amount of variation ; 

 and if both are to be trusted, taken together they point not only to the for- 

 mation of hydrargyrates in the amalgam, but also to polymerization. Ram- 

 say's results, nevertheless, need confirmation before they can be accepted 

 without question, as they are not very numerous, and vary considerably 

 among themselves. Further treatment of the matter must be postponed until 

 more knowledge has been obtained concerning these osmotic pressures. The 

 subject is being studied further in this laboratory. 



The case of zinc may be reviewed more briefly, although it also presents 

 very interesting features. Here, instead of giving too high an electromotive 

 force, the zinc amalgams give one less than the theoretical. A part of this 

 deficiency is to be ascribed to the thermal effect depicted by the formula of 

 Cady ; but as is shown on page 59 this formula explains only one-third of the 

 total deviation. In view of the outcome of the preceding discussion, it seems 

 necessary to refer the otherwise unexplained deficiency to the polymeriza- 

 tion of a part of the zinc. 



This assumption of polymerization is supported by all the other facts 

 bearing upon the question. In the first place, we have found that the dilu- 

 tion of a 1 per cent amalgam absorbs considerable heat, showing that the 

 same reaction which occurs on amalgamating is still occurring and the cool- 

 ing part of this reaction must be supposed to consist in the disintegration of 

 the zinc. However, this effect must not be too hastily connected with the 



