A treatise on the theory of solution including the phenomena of electrolysis . olutionand vapour. It resembles the corresponding curve of ourformer diagram, except that instead of showing the vapourpressure of a pure substance, it represents that of a solution,saturated with salt at each temperature. Since the presence ofsalt lowers the vapour pressure of a liquid, this curve lies belowthat for the pure solvent, unless the solute itself be volatile toan ? appreciable extent, a case which will be considered the solubility increases with the temperature, the curveOA will also rise les
A treatise on the theory of solution including the phenomena of electrolysis . olutionand vapour. It resembles the corresponding curve of ourformer diagram, except that instead of showing the vapourpressure of a pure substance, it represents that of a solution,saturated with salt at each temperature. Since the presence ofsalt lowers the vapour pressure of a liquid, this curve lies belowthat for the pure solvent, unless the solute itself be volatile toan ? appreciable extent, a case which will be considered the solubility increases with the temperature, the curveOA will also rise less steeply than that for the pure solvent, forthe lowering of vapour pressure due to the solute will constantlyincrease. The curve will end at a critical point for the st)lution, CH. Ill] THE PHASE RULE. TWO COMPONENTS, SOLUTIONS 51 at which the solid may melt and either give another quadruplepoint or mix perfectly with the solution. Another possibilityis that by decreased solubility or increased vapour pressure theliquid and vapour may come to have the same composition. D. Salt Vapour Fig. 13. Again returning to the quadruple point 0 on Fig. 13 letice, instead of salt, be present in excess. The addition of heatcauses ice to melt and thus solvent to be formed and salt dis-solved. This proceeds at a constant temperature till all thesalt is dissolved. A further supply of heat melts more ice, andnow the solvent formed from it dilutes the solution, whichtherefore ceases to be saturated. As long as ice remains, wehave an equilibrium between it and an unsaturated solution,that is, we advance along a curve, giving the freezing points ofsolutions of constantly decreasing concentration, ending at B,the freezing point of the pure solvent, when the amount of icewhich has been melted is enough to make the concentration of 4—2 52 SOLUTION AND ELECTROLYSIS [CH. Ill the solution negligible. From the point B may be drawn thesame liquid-vapour and liquid-solid curves which we drew forour one c
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