ON SOLUBILITY. 42? 



law Page and Reightley " found higher values for the solubility 

 of sodium and potassium chlorides, nitrates, and sulphates when 

 obtained by the method of cooling than when water was saturated with 

 the salt at the required temperature. 



In the same year Oudemans iS lamented the discordance of many 

 results recorded for the solubility of substances, and pointed out where 

 many errors arose, particularly the difficulty in obtaining a perfectly 

 saturated solution. 



„„ To avoid supersaturation Limpricht 55 found it necessary to 



allow the solution to stand in a cellar for several weeks at 

 constant temperature. 



Victor Meyer 57 showed that the same end could be rapidly attained 

 by placing a large test-tube containing a hot saturated solution in a 

 bath and stirring until the solution and the bath were at the same 

 temperature, allowing to stand for two hours and again stirring before 

 filtering off a sample through a dry filter, the temperature being recorded. 

 The estimations were carried out by evaporating 10-30 c.cms. of 

 solution. 



He also described an apparatus 5S for enabling a solvent to be 

 saturated and the solution filtered into a receiving vessel, the whole 

 operation being earned out in the vapour of some constantly boiling 

 liquid. 



An exact method of determining solubility was next published by 

 Lajoux. 6i The solvent was heated with the substance to the required 

 temperature, and a portion of the solution taken by means of a 

 jacketed syphon fitted with a filtering plug of cottonwool. 

 10-70 Koelder 79 modified V. Meyer's apparatus, so that the whole 



operation, including filtration into an empty vessel, could be 

 carried out beneath the surface of the liquid forming the bath. 



Hannay and Hogarth*" used a modified form of Andrews' 

 apparatus * for their work on the solubility of solids in gases. 



De Coppet 9T used a completely enclosed copper bath with 

 glass windows on two sides, containing 18 litres of glycerine. The 

 temperature was kept within ± 0°'l 0. by using the expansion of the 

 entire mass of liquid in the bath as a thermoregulator. For tempera- 

 tures below 0° saturated solutions of salts took the place of the glycerine. 

 Nine boiling-tubes were hermetically fixed in the top of the bath, three 

 of which were used to read its temperature. The remaining boiling- 

 tubes were closed with corks through each of which passed (1) a 

 thermometer, (2) a stirrer, (3) a short tube and rubber compression 

 pear, (4) a syphon through which, by compressing the pear, a sample 

 of clear solution was ejected without loss by evaporation. 



The solutions were stirred for at least two hours before allowing to 

 settle. 



Nicol 98 described a bath and thermoregulator by means of which he 

 reduced the temperature variation to 0°'05 at 20° C. 



For each determination 102 two boiling-tubes were used, con- 

 taining salt and water and supersaturated solution respectively 

 After being stirred for twenty-four hours by a current of moist air, the 

 * Vide Trans. Royal Soc, 1869, 159, 583. 



