84 SCIENTIFIC AMUSEMENTS. 



and consequently containing a considerable admixture of air, it 

 will be found that when the ammonia is all absorbed, the remain- 

 ing air is practically unchanged. 



Expt. 79. To separate Ammonia Gas and Air from one another. 

 Place a jar or bottle mouth downwards over the delivery tube 

 attached to a flask in which a strong solution of ammonia is being- 

 warmed, as in Expt. 74, but instead of waiting some little time to 

 allow of the displacement of the whole of the air by the ammonia 

 gas, remove the jar after a few seconds, so that only a small portion 

 of the air in it is displaced. Place the jar mouth downwards in a 

 basin of water, and allow it to stand for half an hour ; by this time 

 all the ammonia in the jar will probably be absorbed by the water ; 

 to make sure, cork the jar under water with a greased cork, so that 

 some water is retained in the jar, take it out and shake up vigorously; 

 then replace it in the basin mouth down wards, and remove the 

 cork, so as to allow more water to enter should the shaking have 

 produced any further diminution in bulk of the gas inside the jar 

 by virtue of absorption of ammonia, Again cork, and remove the 

 jar, and stand it on a table mouth upwards. Uncork the jar, and 

 introduce a lighted taper at the end of a wire (fig. 41). It will 

 be seen that the taper burns in exactly the same way as it would 

 do in the same jar if filled with ordinary air (easily effected by 

 filling the jar with water, and then pouring out the water so as to 

 allow air to enter and fill the jar) ; thus showing that the air 

 equally mixed with the ammonia gas is practically unchanged. 

 If too much ammonia have not been added, it will be found also 

 that the air left in the jar unabsorbed, after shaking up with water, 

 will have little or no smell of ammonia, showing that all, or nearly 

 all, of the ammonia gas in the mixture has been removed by the 

 solvent action of the water. 



If instead of water a weak solution of hydrochloric or sulphuric 

 acid be used, an absolutely complete removal of all the ammonia 

 will be effected, as the solvent action of the water alone will be 

 intensified by the chemical action of the acid. 



Owing to the different solubility of gases in water and other 

 solvents, and the tendency under suitable conditions of gases to 

 evaporate or pass off out of solution, it results that a thin stratum 

 of liquid, or a film of water coating a porous material, or even a 

 soap bubble, will exert a separating action on mixed gases brought 

 into contact with the film. Thus a soap bubble filled with one 

 kind of gas (e.g., with carbon dioxide, or with ordinary coal gas), 

 and allowed to stand in the air for some time, will cause a con- 

 siderable alteration in the composition of the gas inside to take 

 place, because the constituents of the external air will dissolve in 



