ON WATKK' AND ITS COMPOUNDS 61 



column, and if there be sufficient water to dissolve the gas, all the 

 ammonia \vi\\ be absorbed by the water. The water is introduced into 

 tin- cylinder by a glass pipette, with a bent end. Its bent end is put 

 into water, and the air is sucked out from the upper end. When full 

 of water, its upper end is closed with the finger, and the bent end placed 

 in the mercury bath under the orifice of the cylinder. The water will 

 then be forced from the pipette by the atmospheric pressure, and will 

 i-i.se to the surface of the mercury in the cylinder owing to its lightness. 

 The solubility of a gas like ammonia may be demonstrated by taking a 

 flask full of the gas, and closed by a cork with a tube passing through 

 it. On placing the tube under water, the water will rise into the flask 

 (this may be accelerated by heating the flask), and begin to play like a 

 fountain inside it. Both the rising of the mercury and the fountain 

 clearly show the considerable affinity of water for ammonia gas, and the 

 force acting in this dissolution is rendered evident. For both the homo- 

 geneous intermixture of gases (diffusion) and the process of solution a 

 certain period of time is required, which depends, not only on the sur- 

 face of the participating substances, but also on their nature. This is 

 seen from experiment. Prepared solutions of different substances 

 heavier than water, such as salt or sugar, are poured into tall jars. 

 Pure water is then most carefully poured into these jars (through a 

 funnel) on to the top of the solutions, so as not to disturb the lower 

 stratum, and the jars are then left undisturbed. The line of demarca- 

 tion between the solution and the pure water will be visible, owing to 

 their different co-efficients of refraction. Notwithstanding that the 

 solutions taken are heavier than water, after some time complete inter- 

 mixture will ensue. Gay-Lussac convinced himself of this fact by 

 this particular experiment, which he conducted in the cellars under the 

 Paris Astronomical Observatory. These cellars are well known as the 

 locality where numerous interesting researches have been conducted, 

 because, owing to their depth under ground, they have a uniform tem- 

 perature during the w r hole year ; the temperature does not change 

 during the day, and this was indispensable for the experiments on the 

 diffusion of solutions, in order that no doubt in their results should 

 arise from a daily change of temperature (the experiment lasted several 

 months), which would set up currents in the liquids and intermix their 

 strata. Notwithstanding the uniformity of the temperature, the sub- 

 stance in solution in time ascended into the water and distributed itself 

 uniformly through it, proving that there exists between water and a 

 substance dissolved in it a particular kind of attraction or striving for 

 mutual interpenetration in opposition to the force of gravity. Further, 

 this effort, or rate of diffusion, is different for salt or sugar or for 



