CHAPTER XIX. 



THERMODYNAMICS OF CHANGE OF STATE AND 

 OF SOLUTIONS. 



First Latent Heat Equation Volume of Saturated Steam Triple Point and Dif- 

 ference of Vapour- Pressures of Ice and Water below C. Second Latent Heat 

 Equation Alteration of Vapour-Pressure with Curvature of Liquid Surface 

 Connection with Change in Melting-Point by Pressure Solutions Vapour- 

 Pressure less than that of the Solvent Osmotic Pressure Raising of Boiling 

 Point Lowering of Melting-Point Semi-Permeable Membranes Van'!. Hoff's 

 Application of Thermodynamics Molecular Theory of Osmotic Pressure. 



The First Latent Heat Equation. If a substance is at such a 

 temperature, that with suitable pressure and volume it can exist in two 



B! M 



FIG. 172. 



states at once, the two being in equilibrium with each other, then the 

 isothermals on the indicator diagram will have a horizontal position. 

 For example steam and water at 100 C. may coexist and the isothermal 

 for 1 gramme at 100 will be represented by a curve, of which the 

 general course only (it is quite out of scale) is represented by ABOD, 

 Fig. 172. AB is water, BO is steam and water at 100 and 1 atmos- 

 phere, and CD is steam. If the volume is fixed, say at QM, then the 

 proportions of steam and water will be fixed, and they will be in 



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