PHYSICS. 441 



be couclnded therefrom that the force on which solution (lei)en(ls varies 

 with the degree of concentration. Still, another conclusion may be ar- 

 rived at if Grassy's measurements of the decrease of volumes of ^STaCl 

 and of CaClz be taken into account. Interpolation shows that these so- 

 lutions are reduced in volume by pressure as the amount of the dis- 

 solved salt varies : and the reduction of volume which accompanies the 

 solution enables ns to calculate the corresponding^ pressure. It ap- 

 pears that to each molecule of KaCl dissolved in 100 parts of water cor- 

 responds a nearly i)ermanent pressure of about 120 atmosi)lieres, what, 

 ever be the degree of concentration. I'or CaClz the pressure also re- 

 mains constant, but is nearly three times as great. Thus, if the tendency 

 towards solution be measured by i)ressure, it results, for the two salts 

 above mentioned, tl.at the first amounts of salt dissolved exert the same 

 pressure as the last, which bring the solution near to saturation. {Na- 

 ture, March, 1S84, xxix, 512.) 



Nicol has published a series of papers on salt solutions. In the first 

 he considers the phenomenon of equilibrium in these solutions, and con- 

 cludes that when salt solutions are mixed the tendency is to form th« 

 system which will occupy the smallest volume, since then the equilib 

 lium is stable. In the second he discusses the saturation of sait soki- 

 tions, and finds that, as a general rule, the solubility of two salts 

 together is greater than when separate. In the third he continues the dis- 

 cussion on the molecular volumes of salt solutions, and treats especially 

 of water of crystallization. He points out that water of crystallization 

 has no elfect on the molecular volume of a salt in solution ; and 

 hence draws the inference that in all probability water of ciystallization 

 does not exist in solution. In the fourth ])aper he gives the results ot 

 his investigations on the nature of solution, particularly on the boiling 

 points of salts solutions; and he shows that by rise of temi»eratuie the 

 attraction of salt for salt is so greatly diminished that it is equivalent 

 to an increase in attraction of salt for water. {Plril. Mag., Fel)ruaiy, 

 June, September, October, 1884, xvil, 150, 537 ; xviii, 170, 304.) 



Guthrie also has continued his researches upon solution, aiid has 

 published the results of a study of the ammonia group (including the 

 ethylamiues and aniline) in its behavior with water, and also the results 

 obtained by shifting the temperatures up on the scale until the solid 

 fuses, so as to establish the continuity of the phenomena of fusion with 

 those of solution. He establishes the fact that certain bodies originally 

 solid may at liigh temperatures become miscible with water in all pro- 

 portions — a fact of great geologic interest, since it throws light on the 

 pyrohydration of igneous formations, as cryohydration has done for 

 floes. {PItil. Mag., Y, xviii, 22, 105, July, August, 1884.) 



3. 0/ Gases. 



Andreas proposes the following lecture experiment to illustrate 

 Boyle's .law : In a glass tube about a meter long and from l.J'"™ to 2""" 



