e^2 



TRANS. ST. LOUIS ACAD. SCIENCE. 



It is noteworthy that formic acid only gives a negative thermal 

 effect when uniting with 20 equivalents of water. Evidently the 

 lieat of hydration must be a compound factor, the resultant of 

 two antagonistic thermal effects. 



The other three acids are quite similar to one another. The 

 thermal effects observed arc first negative, then positive, in each 

 instance. A glance at Fig. III. will show this similarity very 

 nicely. Formic acid at fiist attains to a maximum positi^^e ther- 

 mal effect at the third hydrate ; acetic, propionic and butyric acids 

 attain to a maximum negative thermal effect at their fourth hy- 

 drates. All four curves, from these points on, approach the zero 

 line of no thermal evolution more or less gradually, and then rise 

 to positive thermal effects, in every instance. The higher the mo- 

 lecular weight, the lower the curve descends in the area of nega- 

 tive thermal effect. 



GENERAL CONCLUSIONS. 



We proposed to examine in this research whether or no there 

 was any relationship to be found between certain of the physical 

 properties of the four fatty acids — formic, acetic, propionic, and 

 butyric — an inference that we should be led to draw from their 

 belonging- to the same cheniical series. 



In general the specific gravities, specific heats and heats of hy- 

 dration have unequivocally been shown to be related wdien com- 

 pared for the four acids. The effect of increasing molecular weight 

 has been noticed everywhere in its action on the above physical 

 properties. However, in the examination of the lower hydrates 

 the differences were often such as to make us despair of drawing 

 any analogy whatever. This is only what we should expect. We 

 can most positively answer the question that we put to ourselves 



