42 G KEPORTS ON THE STATE OF SCIENCE. 



For convenience of publication it was deemed desirable that this 

 report be divided into two parts, the first part to record work published 

 up to and including 1895, the second part up to and including 1910. 



II. Methods of Determination. 



The rapid advance made in the construction of scientific apparatus 

 within recent years has necessarily detracted much from the value of the 

 early work on solubility by enabling a far greater degree of accuracy 

 to be obtained at the present time. 



It is, however, to be lamented that notwithstanding most skilful 

 manipulation and the use of improved apparatus, some of the more 

 recent published work loses in value from the fact that no detailed 

 description is given of the method employed to obtain the results 

 published. 



The purpose of this section is not so much to give a complete record 

 of the various methods employed for determining the solubility of 

 any particular substance, but rather to indicate those of greater interest, 

 and more especially to emphasise the importance of describing the 

 method used so that the value of the results of work on this subject 

 may be properly judged. 



A. — Solubility of Solids. 



The records of work to elucidate the phenomenon of solubility 

 carried out prior to the middle of the nineteenth century are possessed 

 only of . historical interest. 



Poggiale 12 made particular mention of the difficulty in 

 !843. }jt, a i n i n g perfectly saturated solutions. 



He made use of the following two methods given by Gay-Lussac : — 



(1) Gradually heating water with excess of salt. 



(2) Cooling a hot saturated solution. 



He stated that both these methods are valid provided always pre- 

 cautions ore taken to shake the mixture repeatedly at constant tempera- 

 ture for about three hours. The solubilities were estimated by evapo- 

 rating and weighing the residue. 



In reviewing his previous work * Kremers 21 found that his 

 1865. ear i; er values, obtained by allowing a hot saturated solution to 

 cool to the room temperature and immediately taking a sample, did not 

 agree well with those obtained either by Gay-Lussac or by Poggiale ; 

 he attributed this to his solutions being supersaturated. 



He made a fresh series of determinations, allowing the hot 

 saturated solutions to cool to 0° U. and then immersing them in ice 

 for prolonged periods with frequent shaking, and found that after one 

 hour the composition of the solution did not alter, even after standing 



for ten hours. , 



From this he concluded that supersaturation may be avoided by 

 shaking for one hour at constant temperature. He repeated his previous 

 work making use of this method. 



* Pogg., 94, 255 et scq. 



