PROGRESS IN PHYSICAL CHEMISTRY. 307 



iodide, which was decomposed when equilibrium was 

 attained, varied with the temperature. At 290° it was 

 0*1637; at 518°, 0*2363 ; at 320 , however, it was only 

 0*1601, and a minimum occurred at this temperature. This 

 remarkable fact points to the conclusion that at 320° the 

 heat of formation is nil. Such a result is in harmony with 

 thermochemical considerations, for at ordinary temperatures 

 the heat of formation of hydrogen iodide is negative, while 

 at high temperatures, since the amount of decomposition 

 increases with the temperature, the heat of formation must 

 be positive, and hence at some intermediate temperature it 

 must be nil. Bodenstein also finds that pressure modifies 

 the condition of equilibrium by increasing the decom- 

 position. According to the law of mass action, pressure 

 should produce no effect. Hence there is probably some 

 secondary reaction involved whereby the volume of the 

 system is diminished, and does not remain constant, as in 

 the case of the normal reaction. The effect of pressure 

 and temperature on the velocity of decomposition was also 

 obtained ; the velocity constant is almost proportional to 

 the pressure. 



Carrara (157) has studied the velocity of formation of 

 Me, Et SI. At o°, if it be produced from Me 2 S and Et I, 

 the velocity constant is 0*00027, whereas if Me EtS and 

 Mel be used the constant is 0*01223, or almost fifty times 

 greater. Again if Me Et 2 SI be formed from Et 2 S and 

 Mel, the constant is almost fifty times greater than it is 

 when Me EtS and EtI are used. 



The velocity of hydrolysis of ethers is definitely con- 

 nected with their chemical nature ; indeed, De Hemptinne 

 (158) finds that if the constants for one series, and also that 

 of a single member of another series, be known, the constants 

 of all the members of the second series may be calculated. 

 Certain reactions are of course only possible in certain 

 solvents ; an interesting study of the effect of the solvent 

 has been made by Otto (159). 



From observations of its influence on the saponification 

 of methyl acetate, Walker concludes that in aqueous solution 

 Na 2 S exists as Na HS and Na HO (160). Using the rate 



