68 PRINCIPLES OF CHEMISTRY 



important to turn attention to the existence of the solid imsohi1>J<' 

 substances of nature, because on them depends the shape of the 



cover 2^, which can be firmly pressed down on to the wide tube, and hermetically closes it 

 by means of an india-rubber ring. The tube r r can be raised at will, and so by pouring mer- 

 cury into the funnel the height of the column of mercury, which produces pressure inside 

 the apparatus, can be increased. The pressure can also be diminished at will, by letting 

 mercury out through the cock r, A graduated tube e, containing the gas and liquid to be 

 experimented on, is placed inside the wide tube. This tube is graduated in millimetres 

 for determining the pressure, and it is calibrated for volumes, so that the number of 

 volumes occupied by the gas and liquid dissolving it can be easily calculated. This tube 

 can also be easily removed from the apparatus. To the right of the figure, the lower 

 portion of this tube when removed from the apparatus is shown. It will be observed 

 that its lower end is furnished with a male screw 6, fitting in a nut a. The lower 

 surface of the nut a is covered with india-rubber, so that on screwing up the tube its 

 lower end presses upon the india-rubber, and thus hermetically closes the whole tube, for 

 its upper end is fused up. The nut a is furnished with arms c c, and in the stand f 

 there are corresponding spaces, so that when the screwed-up internal tube is fixed into 

 stand/, the arms c c fix into these spaces cut in/. This enables the internal tube to In- 

 fixed on to the stand/. When the internal tube is fixed in the stand, the wide tube is put 

 into its right position, and mercury and water are poured into the space between the two 

 tubes, and communication is opened between the inside of the tube e and the mercury 

 between the interior and exterior tubes. This is done by either revolving the interior 

 tube e, or by a key turning the nut about the bottom part of/. The tube e is filled with 

 gas and water as follows : the tube is removed from the apparatus, filled with mercury, 

 and the gas to be experimented on is passed into it. The volume of the gas is measured, 

 the temperature and pressure determined, and the volume it would occupy at and 

 760 mm. calculated. A known volume of water is then introduced into the tube. The 

 water must be previously boiled, so as to be quite freed from air in solution. The tube is 

 then closed by screwing it down on to the india-rubber on the nut. It is then fixed on to 

 the stand/, mercury and water are poured into the intervening space between it and the 

 exterior tube, which is then screwed up and closed by the cover j?, and the whole 

 apparatus is left at rest for some time, so that the tube e, and the gas in it, may attain the 

 same temperature as that of the surrounding water, which is marked by a thermometer 

 Jc tied to the tube e. The interior tube is then again closed by revolving it in the nut, 

 the cover^? again shut, and the whole apparatus is shaken in order that the gas in the 

 tube e may entirely saturate the water. After several shakings, the tube e is again 

 opened by revolving it in the nut, and the apparatus is left at rest for a certain time ; it is 

 then closed and again shaken, and so on until the volume of gas does not diminish after 

 a fresh shaking that is, until saturation ensues. Observations are then made of the 

 temperature, the height of the mercury in the interior tube, and the level of the water in 

 it, and also of the level of the mercury and water in the exterior tube. All these data 

 are necessary in order to calculate the pressure under which the solution of the gas takes 

 place, and what volume of gas remains undissolved, and also the quantity of water which 

 serves as the solvent. By varying the temperature of the surrounding water, the amount 

 of gas dissolved at various temperatures may be determined. Bunsen, Carius, and 

 many others determined the solution of various gases in water, alcohol, and certain 

 other liquids, by means of this apparatus. If in a determination of this kind it is found 

 that n cubic centimetres of water at a pressure h dissolve in cubic centimetres of a 

 given gas, measured at and 760 mm., when the temperature under which solution 

 took place was t and pressure h mm., then it follows that at the temperature / flic, 



co-efficient of solubility of the gas in 1 volume of the liquid will be equal to m x ' ' 



This formula is very clearly understood from the fact that the co-efficient of solubility 

 of gases is that quantity measured at and 760 mm., which is absorbed at a pressure 



