636 



TRANS. ST. LOUIS ACAD. SCIENCE. 



For butyric acid the values c'lc' and curve also reach their first 

 maximum at the second hydrate. A slij^ht minimum is to be ob- 

 served at the third hydrate. The further course shows no marked 

 deviations from gradual approach to unity. 



COMPARISON OF THE VALUES C ■ c' FOR THE FOUR ACIDS. 



Formic acid appears to differ very much from the other three 

 -at first sight. Closer inspection, however, will show that this is 

 by no means the case. The increment of specific heat on addi- 

 tion of the first half molecule of water to formic acid is greater 

 by far than for any of the other acids, as is also the increment in 

 density. For acetic acid the circumstances are different. Its first 

 maximum lies at the second hydrate, whilst that of formic acid 

 lies at i^ hydrate. At 2 J hydrate of acetic acid there occurs the 

 first minimum, followed by a maximum at the fourth hydrate, 

 and a second minimum at the sixth hydrate, in which respects it 

 agrees exactly with formic acid. Propionic, as well as butyric 

 acid, have their first maxima at the second hydrate just as acetic 

 acid has. Their first minima, however, occur at their third 

 hydrates; these are followed by maxiina again at their fiftTi hy- 

 drates. Propionic acid seems to show another minimum at its 

 eighth hydrate. 



