SEPARATION OF GASES BY MEANS OF SOLVENTS. 83 



large and not sufficiently strong, it may happen that it will be 

 crushed in and broken by the pressure of the atmosphere upon it, 

 when the counterbalancing internal pressure is greatly diminished 

 by the rapid absorption of the ammonia gas by the water. 



For other experiments in which ammonia gas or solution takes 

 a part, vide Nos. 79, 114, 124, 138, 145, 160, 198, 214, &c. 



Expt. 78. Absorption of Ammonia by Ice. The tendency of 

 water to absorb ammonia gas is so strong that 

 it is exhibited even when the water is frozen 

 solid ; the absorption of the gas by the outer 

 surface of the ice develops sufficient heat to 

 thaw the next layer underneath, and the water 

 so produced absorbs more ammonia, evolving 

 more heat, and so the action goes on until all 

 the gas is absorbed, and all the ice melted, if 

 the two are in suitable proportions. 



Collect a jar of ammonia, as in Expt. 75, 

 and throw into it a lump of ice the size of a 

 small walnut; the ice will be soon melted, 

 and a solution of ammonia formed. 



A better way of showing the same result is 

 to float a piece of ice on the surface of a basin 

 of quicksilver, and then place over it a narrow 

 tube sealed at one end, and full of ammonia 

 gas (fig. 46). The ice will absorb the ammonia, 

 and become liquid; whilst the mercury will 

 being forced up by the atmospheric pressure. 



Fig. 46. 

 rise in the tube, 



Separation of Gases from one another by means of Solvents. 



We have seen (Expts. 66, 67), that it is often possible to bring 

 about a more or less complete separation of solids mixed together 

 by taking advantage of the fact that one of them is readily soluble 

 in a particular solvent which will not dissolve the other consti- 

 tuents of the mixture freely ; similarly sulphate of copper, camphor, 

 and sand may be separated (Expt. 68) by first treating the 

 mixture with alcohol, which dissolves the camphor, leaving the 

 other two undissolved, and then with water, which dissolves the 

 sulphate of copper, leaving the sand undissolved. In similar 

 fashion, gases when mixed together may often be separated by 

 means of solvents. Thus Expt. 76 shows how ammonia gas and 

 air may be separated by means of water or spirit in which the 

 ammonia dissolves freely, and the air but little. If the experi- 

 ment be repeated with a jar only partly filled with ammonia gas, 



