504 Dr. Redtenbacher on a Class of Organic Acids. 



solution of the easily soluble acids was neutralized by car- 

 bonate of soda and evaporated to a syrup. Acetate of soda 

 first crystallized out. The mother-liquor was decomposed by 

 sulphuric acid, the floating oily stratum drawn off, and the 

 acetic, metacetonic and butyric acids were partly separated 

 from one another by their boiling-points ; the acetic acid and 

 the metacetonic were determined by a silver salt, and the bu- 

 tyric acid by a barytic salt. It may be conceived that the 

 separation of these nine acids, possessing such similar pro- 

 perties, was effected with much difficulty. It is already trou- 

 blesome to separate the four volatile acids of butter by means 

 of the crystallization of the barytic salts ; nearly one-third of 

 the barytic salts remain as an inseparable mixture. The vo- 

 latile acids of butter differ in the amount of the factor n, 

 but not more than 4, while the series with which I was oc- 

 cupied differed only 2. The similarity of the properties of 

 the barytic salt, or, what is the same thing, the difficulty of 

 their separation, was therefore twice as great, I had there- 

 fore a large quantity of the mixed barytic salts which was unfit 

 for examination ; it would have been impossible to exhibit 

 separately all the acids unless I had had 4 oz. of the mixed 

 volatile acids. 



Before I made use of the barytic salts I tried the separa- 

 tion of the hydrated acids by means of their boiling-point. 

 According to recent experiments of Kopp and Fehling, it ap- 

 pears that the hydrated acids (CH n ) 4 increase in their boil- 

 ing-point about 20° C. when the factor n is augmented by 2. 

 But when I undertook the distillation, the thermometer rose 

 so regularly from degree to degree that I soon discovered the 

 futility of this mode of separation. A portion of the acid hy- 

 drates which came over at the boiling-points of butyric acid, 

 164° C. and about 4° lower, were converted into silver salts; 

 they proved to be upon examination a mixture of three acids, 

 — the butyric acid, the next lower, the metacetonic, and the 

 next higher, the valerianic acid. Therefore, as a complete 

 separation could not be effected by distillation of the hydrated 

 acids, I did not attempt the separation by means of the ethyle 

 compounds, which would in all probability have acted in the 

 same manner. 



For the less volatile acids, from valerianic to capric acids, 

 I had recourse to the barytic salts. By gentle evaporation 

 and crystallization I obtained a series of about twenty cry- 

 stallizations, and by means of an examination according to 

 their known atomic weights, I was enabled to refer the sepa- 

 rate crystallizations to their different acids, and by subsequent 

 recrystallization of the different portions to separate them 



