1886.] resulting from an increase in the supply of heat. 371 



has a boiling point somewhere between 74° and 85°. This sub- 

 stance I take to be chiefly ethyl iso-cyanide which boils at 78°. At 

 any rate the distillate smells strongly of that substance. The mix- 

 ture does not give the liquid with the lower boiling point, at least 

 in any quantity, until the bath reaches 168°. We may suppose 

 that the flask and the layer of the mixture next the bottom and 

 sides reach about the same temperature as the bath, and that this 

 layer is then resolved into the iso-cyanide and potassium oxalate. 

 This may possibly be accompanied by a storage of some of the 

 energy supplied, but whether that be so or not, the evaporation of 

 the volatile compound would depress the temperature of the bulk 

 of the liquid. When the bath falls below 168° only the less volatile 

 liquid is formed in quantity, and the mixture rises to the boiling 

 point of the latter. In both cases the temperature of the mixture 

 is kept down by the evaporation of a volatile compound formed by 

 the action of heat upon it, but at the higher temperature the com- 

 pound formed has the lower boiling point. 



Although I have no doubt that the compounds formed are 

 propio-nitrile and the iso-cyanide, this has not been proved yet. 

 The distillates are by no means pure single substances, or easy of 

 purification, so that the interesting chemical question as to the 

 formation of propio-nitrile at one temperature and of its isomer at 

 a higher is not yet fully solved. We know from Thomsen's 

 researches that the heat of formation of propio-nitrile is negative, 

 that is to say it is formed with a storage of energy ; but I have not 

 been able to meet with any determination of the heat of formation 

 of the iso-cyanide. Considering the large storage of energy in the 

 formation of hydro-cyanic acid it is probable that the storage in 

 the iso-cyanide exceeds that in propio-nitrile. 



It occurred to me that, if the explanation I have given of the 

 changes of temperature were correct, similar phenomena must 

 present themselves in other cases where chemical reactions pro- 

 ducing compounds more volatile than the reagents are determined 

 by particular high temperatures. For example common ether is 

 produced by the reaction of alcohol on ethyl-sulphuric acid at a 

 temperature which is given at about 145°. At temperatures below 

 that the distillate is chiefly alcohol. This case is not so simple as 

 the former because when ether is formed water is also formed at 

 the same time. Nevertheless until the bath gets hot enough to 

 determine the formation of ether the temperature of the mixture 

 and its vapour will be dependent on the boiling point of alcohol, 

 while when the bath gets hot enough ether and water will be 

 formed, and the lower boiling point of ether will determine a lower 

 temperature of the parts of the mixture not near the sides of the 

 flask and as well as of the vapour. To test this I asked Mr Robinson 

 to make an experiment with alcohol and sulphuric acid in the 



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