Chemistry and Physics. 493 



pressed in 10 -9 centimeters. The following are the results ob- 

 tained. 



H |H 2 I Br (ON) CI K (NH 4 ) (N0 3 ) (01O«) £K 2 i(S0 4 ) Ag 

 15 32 91 91 95 96 97 99 100 111 111 111 111 



KNH 4 ) 2 i(C0 3 ) £Ag 2 Na F £Ba |Cu £Sr ^Ca $Mg (0 2 H 3 O 2 ) 

 117 119 129 132 135 138 138 141 148 160 160 



£Na 2 i(S0 4 ) Li \Zn iMg ^Zn $Cu £Li 



165 165* 170 175 218* 239* 239* 251* 



The values marked with a star were obtained from the electric 

 conductivity of magnesium, copper, and zinc sulphates. It will 

 be noted that not only do the linear dimensions of molecules vary 

 very widely, but that the diameter of a double molecule is greater 

 than twice that of a single molecule ; a necessary result of uniting 

 two equal spheres. Moreover, the values for allied elements are 

 nearly the same ; as in the group chlorine, iodine and bromine; 

 or bai'iumj strontium and calcium. Again if the number of mole- 

 cules in unit volume is proportional to the molecular volume, then 

 by multiplying this volume by the molecular weight, we should 

 obtain values proportional to the densities of the elements con- 

 cerned. Since this relation does not hold good, except for closely 

 allied elements, it follows that the ultimate particles of different 

 molecules are differently arranged. — Monatsheft, viii, 498-507 ; 

 J. Ghem. Soc, liv, A bstr. 217, March, 1888. g. f. b. 



2. On the Chemical Decomposition produced by Pressure. — The 

 researches of Spring have shown that many substances which 

 exert no action upon each other at atmospheric pressure, may be 

 made to combine more or less completely if subjected to a press- 

 ure sufficient to cause a perceptible condensation. Since the sub- 

 stances experimented with had a smaller volume after union than 

 that of their constituents, it became an interesting question to 

 ascertain whether, in the case of a substance whose volume is 

 greater than that of its constituents, the temperature of conver- 

 sion can be lowered by pressure. Spring and van't Hoff have 

 examined this action by submitting finely pulverized copper- 

 calcium acetate to a pressure of 6000 atmospheres at a tempera- 

 ture of 16°. The powder, though reduced to a crystalline mass 

 resembling marble, showed no sign of decomposition. It was then 

 subjected to the action of a screw press at a temperature of 40°. 

 The results were marked, three-quarters of the mass being lique- 

 fied, and becoming solid again when the pressure was removed. 

 The sides of the containing vessel were covered with a coating of 

 copper and small leaves of copper could be picked out of the 

 mass. The dark blue of the acetate had changed to green, inter- 

 spersed with white points indicating the separation into copper 

 acetate and calcium acetate. Since the thermic effect of the com- 

 pression was less than corresponds to a rise of 1°,. the above 

 result must have been due entirely to a change of volume. At 



