636 TRANS. ST. LOUIS ACAD. SCIENCE. 



The results obtained are always deduced at least from dupli- 

 cates, and when these showed greater differences the number of 

 determinations was augmented. 



The only works in similar directions known to me were those 

 oi Favre, Compt. Rend. 50, p. 1150, "On the heats of hydration 

 of acetic acid"j and of Von Reiss, Wied. Ann. x., p. 291, '' Ei- 

 genthmnlichc BezieJumg z-ucisehen Dickie tind spec. Wdrme der 

 Gemische von Essigsdure tind Wasser." I append the results of 

 these authors for the sake of comparison. They differ from mine 

 by amounts lying within the limits of error, as will be seen. 



Previously to making the measurements appended below, my 

 care was directed to insurance of pure materials. The acids used 

 were of Kahlbaum's manufacture. Before experimenting on any 

 of them they were dehydrated by rectification from calcium- 

 chloride and redistillation of the distillate so obtained. In regard 

 to boiling point, specific gravity, and specific heats, they were 

 found to agree very closely with the results obtained by other 

 observers, as will be seen by referring to the data given below. 

 Therefore I am warranted in the conclusion that they were pure. 



The mixtures of the acids with water were made by weighing 

 out each constituent on a chemical balance giving the yV of a 

 milligrame. 



THE SPECIFIC GRAVITIES. 



They were determined by means of a pycnometer with perfo- 

 rated stopper capable of holding 9.9S12 grms. of water at 25° C. 

 The measurements were made in the ordinary way at constant 

 temperature for each series, which was accomplished by im. 

 mersing the flask in a water-bath of constant temperature. The 

 numbers obtained for the duplicates in each case were most con- 

 cordant. The greatest differences amounted to a unit in the third 

 place, and the average difference was about six in the fourth 

 place. In each table the temperature at which the determina- 

 tions were made is indicated. The specific gravities are reduced 

 to the specific gravity of water of the same temperature and not 

 to water of 4° C, as we need these numbers to calculate the 

 condensations. The data given are the mean of duplicates. The 

 first column, headed n, gives the number of equivalents of 

 acid ; the column headed n' gives the total number of equiva- 

 lents of water added to one equivalent of acid ; the column 



