Molecular Constitution of Water. 477 



into dihydrol, and also the heat to effect the solution of the 

 dissociated trihydrol. Let h be the heat absorbed when 

 Pi gramme of dihydrol is mixed with p- 2 =l — P\ gramme of 

 liquid trihydrol, and D the heat absorbed in dissociating a 

 gramme of trihydrol into dihydrol, then for the heat dQ to 

 raise the temperature of a gramme of water by dt we have 



^Q = (piCi +p 2 c 2 )dt + (U + dh/dp 2 )dp a ; 



.'■ c= d § Pl c 1 +p 2 c 2 +(I) + dh/dp 2 ) d ^. . . (25) 



Now e the specific heat of water can be taken as constant 

 at l'O, while c x and c 2 are known from (23), (24), with dp 2 \dt 

 from (7) ; so that the last equation furnishes us with values 

 of T> + dh/dp 2 . as given in the next table, where they are com- 

 pared with those of 78 4- 3290 (•■425 —p 2 ) 2 given in the last row. 







Table XI. 









0° 



20° 



40° 60° 80° 



100° 



120° 



140° 



86 



114 



142 172 200 



223 



241 



255 



86 



114 



143 173 198 



220 



240 



258 



It appears from this that 



■ _D- ^- = 78 + 3290 (-425 -rf; . . , (26) 



.-. -T>p 2 -h =78p 2 -3290(-425-p 2 ) 3 /3 + C: 



and as h — when p 2 = 0, 



C = 84-2. 



Then at 0° with p 2 ='375 we have 



~-375D-/i=113; 



and from the latent heat of fusion of ice we have 



-•625D+A = 64; 



/. D=-177, (27) 



-A=-99^ 2 -3290(-425-p 2 ) 3 /3 + 84-2. . . (28) 



The negative sign of D is the result of dp 2 in (25) being 

 negative ; 177 calories have to be given per gramme of tri- 

 hydrol to change it to dihydrol. This (28) then is the 

 expression for the law of the evolution of heat when liquid 

 trihydrol is dissolved in dihydrol up to a concentration of 

 •425 trihydrol per gramme. 



As water consists mostly of dihydrol while steam is hydro! ,. 

 it follows that the latent heat of evaporation of water is not 



Phil. Mag. S. 5. Vol. 50. No. 306. Nov. 1900. 2 L 



