126 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



jectcd to a pressure of 300 atmospheres at various tempera- 

 tures, from 2 to 48 C, with the very important result that, 

 even at 2, the carbonic acid of such a mixture could not be 

 liquefied under any pressure. Indeed, the " critical point " of 

 carbonic acid proves to be lowered many degrees when that 

 gas is mixed with a non-liquefiable gas, such as nitrogen. 

 15 A, Aug. 29, 1874, 277. 



THE FORCES DEVELOPED BY EVAPORATION AND CONDEN- 

 SATION. 



Professor Osborne Reynolds, in a careful review of the re- 

 markable observations recently made by Mr. Crookes, shows 

 that, according to the kinetic theory of gases, whenever a 

 molecule of liquid is evaporated, and becomes a molecule of 

 gas, it must leave the liquid surface with a velocity equal to 

 that with which the other particles of the gas are rebounding 

 among themselves; that is to say, instead of being first de- 

 tached, it must be shot off with a velocity greater than that 

 of a cannon-ball, and there must be an equal reaction on the 

 surface of the remaining liquid ; the contrary effect takes 

 place in the case of condensation. Applying the necessary 

 mathematical formulae, he finds that, at a temperature of 

 60, the evaporation of one pound of water from a surface 

 is sufficient to maintain a force of 65 foot-pounds for one 

 second, the force being proportional to the square root of 

 the absolute temperature. In the case of mercury the force 

 is only 6 foot pounds instead of 65. And again, whenever 

 heat is communicated from a hot solid surface to a gas, an 

 effect similar to that of evaporation is produced, while for 

 every English unit of heat communicated to steam, at a 

 temperature of 60, the reaction on the surface is equivalent 

 to 0.38 of a pound acting for one secpnd ; but is, for air, 0.55 

 of a pound. 12 A, X., 175. 



THE HEAT PRODUCED BY GALVANIC CURRENTS. 



Since the galvanic effect upon metal wires, by means of 

 which they are made to glow, has acquired a practical im- 

 portance in galvano-caustics, it appears desirable to present, 

 in the clearest manner, the connection between the power of 

 the battery, the dimensions of the -wire, and the resulting 

 phenomenon; and the first attempt at a partial solution of 



