§ 139. SEPARATION OF VOLATILE ACIDS. 119 



I obtained similar results in experiments with cacao butter. 

 Resin could be almost completely freed from ethereal oil at 100° 

 to 110°, and it was only in the case of oils prone to oxidation, 

 such as oil of cloves, that the residual resin A^as somewhat 

 heavier than was expected. (See also § 1.46.) 



Dryiug oDs, would, of course, increase very appreciably in 

 weight. The evaporation and heating would have to be conducted 

 in an atmosphere of carbonic acid {■§ 9). 



The following experiment will serve as, an example of the 

 estimation of ethereal oil in a vegetable substance :i 



Five grams of savin leaves were finely powdered and digested 

 with 25 cc. of petroleum spirit ; 1 cc. of the solution was eva- 

 porated. The residue weighed ,0-0265 gram (com), which de- 

 creased to 0'0175 giam on heating to 110°. 1 cc. contained, 

 therefore, 0*009 gram ethereal oil and 0-0175 , gram resin, or 

 4-5 per cent, of ethereal oil and 8-75 per cent, of resin. 



§ 139. Separation of Volatile Adds. — ^Angelic acid melts at 45° 

 and boils at 185° ; methyl-crptonic acid at 65° and 198° ; crotonic 

 acid, 16° and 160-6° ; capric, 30° and 268° to 270° ; caprylic, 16° 

 to 16-6° and 236° to 237° ; cenaJithic boils at 223' to 224° ; caproic, 

 204° to 206° ; valerianic at 175°; trimethyl acetic, 163^7° to 163-8" 

 (melts at 35-3° to 35-5°); butyric at 163°; isobutyric, 154°- 

 propionic, 140°; acetic, 118° (solidifies at 16-7°); formic, 105°. 

 This difference "in the boiling points of fat^acids permits of their 

 separation from one another by fractional distillation. 



Fractional precipitation by salts of Silver, etc., may also be 

 found useful in separating several of the foregoing volatile acids 

 from one another; certain differences in the solubility of the 

 salts can also sometimes be turned to account. Isobutyric acid, 

 for instance, may be separated by the former method, whilst the 

 sparing solubihty of the silver salt (1 in 100) enables us to isolate 

 acrylic, butyric,. acetic acid, etc. The barium, calcium, and lead 

 salts of some of the acids may be similarly employed ; thus the 

 barium salt of caprylic" acid is soluble in 164 parts of cold water -^ 

 formate of calcium is- insoluble in absolute alcohol ; the lead salt 

 dissolves in 65 parts of water, whilst mercurous formate requires 500 

 parts at the ordinary temperature. Basic formate of lead obtained 



^ See OBse|s work previously referred to. 



" For the estimatiou of valerianic acid, see Zavatti and Scstini, Zeitschr. i. 

 anal. Cbemie, viii. 888, 1869. 



