EFFECT OF PRESSURE ON SOLUBILITY. 79 



description is at Knaresborough near Harrogate, in Yorkshire, and 

 other similar ones in Derbyshire, and many places in Continental 

 Europe and elsewhere. 



Carbonic acid is by no means the only gas contained in natural 

 waters; sulphuretted hydrogen (Expts. 13 and 14) is sometimes 

 present, as in some of the Harrogate and many Continental 

 springs, giving to the water a strong smell of rotten eggs. Waters 

 of this description are extensively employed in the cure of certain 

 complaints, partly by drinking the water, partly by bathing 

 therein. In some places, mostly in volcanic districts, springs 

 exist containing sulphurous acid (Expts. 117, 161, and 238); 

 whilst combustible gases, somewhat akin to ordinary coal gas, are 

 given off' from deep wells in the American petroleum districts and 

 elsewhere, sometimes in such quantity as to be capable of being 

 largely used as fuel for raising steam, smelting metals, and such 

 like manufacturing purposes. 



Circumstances modifying the Solubility of Gases in Liquids. 



It does not at all follow that because a particular liquid, such 

 as water, will dissolve one gas freely, that therefore it will act 

 similarly with a different gas ; just as water will dissolve salt or 

 sugar in considerable quantity, but will fail entirely to dissolve 

 chalk or sand, so is each particular gas possessed of a different 

 power of dissolving in water ; whilst just as a particular substance, 

 such as camphor, will hardly dissolve in water at all, but is freely 

 soluble in a different solvent, alcohol (Expt. 64), so a gas will 

 often dissolve readily in one kind of liquid, but nothing like so 

 freely in another. For example, sulphuretted hydrogen dissolves 

 pretty readily in cold water, communicating to it its peculiar 

 nauseous smell and flavour ; but liquid petroleum and heavy coal 

 oils will hardly dissolve the gas at all. The solubility of gases in 

 liquids, however, is largely affected by circumstances that do not 

 have the same effect on the solubility of solids on liquids ; thus 

 it has been already stated that when the pressure is increased the 

 quantity of gas (carbon dioxide) that a given quantity of water 

 can dissolve is increased too, and vice versa. This is a general law, 

 it being uniformly found that if a given quantity of gas can be 

 dissolved in a certain quantity of any solvent at a particular 

 pressure, twice that quantity of gas can be dissolved when the 

 pressure is doubled, three times when trebled, four times when 

 quadrupled, and so on ; whilst if the pressure is halved or reduced 

 to one-third or one-quarter, &c., the quantity of gas dissolved in 

 each case is similarly reduced to one-half, one-third, one-quarter, 



