LUEDEKING: — PHYSICO-CHEM. STUDIES IN FATTYACID SERIES. 641 



The coutses of the curves, constructed as indicated above, show 

 the thermal effects as they change for the different acids in the 

 course of the dikition. Foimicacid alone gives a positive thermal 

 effect in the formation of its first hydrates. With decreasing mo- 

 lecular weight the negative thermal effects decrease in the forma- 

 tion of the first hydrates for the other three acids, so that for 

 butyric acid the negative thermal effect resultant upon its union 

 with 2 eq. water is greater than for propionic acid, and forthis 

 latter greater than for acetic acid. 



It was, therefore, in accordance with my anticipation that I 

 found the negative thermal effect, resultant upon the union of va- 

 lerianic acid with | eq. of water, still greater than for butyric acid. 



Formic acid, in that it unites with its first half equivalent of 

 water with a positive thermal effect, does not behave at variance 

 with our anticipations. We should expect that this thermal effect 

 would be either very slightly negative, or even positive, from the 

 observations on the other three acids. It may be a mere coinci- 

 dence only, but it is a fact, that the difference in the heats of hy- 

 dration for this first 2 eq. of water between formic and aeetic acids 

 is nearly equal to the- difference between the heats of hydration 

 lor aeetic and propionic acids, being approximately 200 calories. 

 The curves of all four acids show perfect analogy after the dilu- 

 tion has gone on to a certain extent. 



In Table II. I give the actu;il thermal effects, resultant on the 

 union of one molecule of each of the four acids with various 

 equivalents of water. The column headed n^ gives the number of 

 equivalents of Waaler which unite with one equivalent of acid, with 

 evolution of the annexed number of gramm calories. This table 

 is deduced from the previous one. In Fig. IV. will be found curves 

 in which these calories are the ordinates, whilst the number of 

 equivalents of water added are the abscissas. 

 Table II. 



