ON WAT Hi; AND ITS COMPOUNDS 



67 



substance !>' added to water which is already saturated with it, it will 



remain in its original state, ;:nd will not spread through the water. The 



quantity of a substance 



(either l>y volume with 



gases, or by weight with 



solids and liquids) which is 



capable of saturating 100 



parts of water is called the 



co-pftifii-Ht <>f xoltihilitij or 



the sot nullify. Tn 100 grams 



of water at 15, there can 



be dissolved not more than 



35 "86 grams of common 



salt. Consequently, its 



solubility at 15 is equal 



to 35-S6. 21 It is most 



- 1 The solubility, or co-efficient 

 of solubility, of a substance is de- 

 termined by various methods. 

 Either a solution is expressly pre- 

 pared with a clear excess of the 

 soluble substance and saturated 

 at a given temperature, and the 

 quantity of water and of the sub- 

 stance dissolved in it determined 

 by evaporation, desiccation, or 

 other means ; or else, as is done 

 with gases, known quantities of 

 wat-r and of the soluble sub- 

 stance are taken, and the amount 

 remaining undissolved is deter- 

 mined. 



The solubility of a gas in water 

 is determined by means of an ap- 

 paratus called an absorptio- 

 niffcr (fig. 16). It consists of an 

 iron stand/, on which an india-rub- 

 ber ring rests. A wide glass tube 

 is plar-ed on this ring, and is pres- 

 sed down on it by the ring // and 

 fhe screws ii. The tube is thus 

 firmly fixed on the stand. A cock 

 r, communicating with a funnel r, 

 passes into the lower part of the 

 stand. Mercury can be poured 

 into the wide tube through this 

 funnel, which is therefore made 

 of steel, as copper would be 

 affected by the mercury. The 

 upper ring h is furnished with a 



Ktui-rti's alisorjitionieter. Apparatus 

 niiiiiiiL' tlic solubility of gases in liquids. 



leter- 



P 2 



