116 ELEMENTS OF LABORATORY WORK 



CHAPTER VII 



INVESTIGATION OF THE COMPOSITION OF VARIOUS KIND 

 OF MATTER 



75, The Separation of a Complex Body into different kinds 

 of Matter by a Difference in Degree of Solubility in Water. 

 A mixture of barium sulphate and sodium chloride which is 

 apparently homogeneous is added to water in a vessel, and 

 stirred or warmed for some time. The liquid is now poured 

 into another vessel, and water is freely added to the solid 

 which remains, without any further solution, as far as can be 

 seen, taking place. The solid suspended in the water is col- 

 lected, by filtering through porous paper, and then dried upon 

 the paper in a drying chamber. The filtrate, or liquid running 

 through during filtration, can be rejected, but the liquid in 

 which the mixture was first stirred is now made to evaporate 

 in a porcelain dish. A white solid will be found to remain. 

 We have now two solids. One of them is readily soluble in 

 water. The other is insoluble, as may be shown by causing 

 some water which has been in contact with it for some time 

 to evaporate upon a watch-glass. No solid remains after the 

 water has changed into vapour. The two solids may be set 

 aside for future examination. The distinction so far lies 

 solely in their solubility in water. Further distinctions will 

 be found when they are compared under other circumstances. 



A mixture of ammonium oxalate and potassium bromide 

 is now taken, and the whole is found to completely dissolve 

 when warmed in presence of sufficient water. The solution is 

 made stronger by evaporation, until some of the solid begins 

 to separate out in crystals. It is now allowed to cool, and 

 then the liquid is poured away from the needle-shaped crystals 



