§ 139. SEPARATION OF VOLATILE ACIDS. 119 



I obtained similax' results in experiments Avith cacao Initter. 

 Resin could l)e almost completely freed from ethereal oil at 100° 

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

 •such as oil of cloves, that the residual resin was someAvhat 

 heavier than was expected. (See also § 146.) 



Drying oils Avould, of course, increase A'ery api^recial ily in 

 Aveight. The evaporation and heating Avould have to be conducted 

 in an atmosphere of carbonic acid (§ 9). 



The following experiment Avill serve as an example of the 

 estimation of ethereal oil in a vegetable substance :^ 



Five grams of savin leaves Averc finely powdered and digested 

 Avith 2-5 cc. of petroleum spirit ; 1 cc. of the solution Avas eva- 

 porated. The residue Aveighed 0-0265 gram (corr.), Avhich de- 

 creased to 0"0175 gram on heating to 110". 1 cc. contained, 

 therefore, 0"009 gram ethereal oil and 0"017o gram resin, or 

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



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

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

 acid, 16° and 160'5° ; capric, 30° and 268° to 270° ; caprylic, 16° 

 to 16-5° and 236° to 237° ; cenanthic 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 j)erniits of their 

 separation from one another by fractional distillation. 



Fractional precii:)itation 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. Isobut3'ric acid, 

 for instance, may be separated l)y the former method, Avhilst the 

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

 acrylic, iDutyric, 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 Avater ;^ 

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

 dissolves in 65 parts of Avater, Avhilst mercurous formate requires 500 

 parts at the ordinary temperature. Basic formate of lead ol>tained 



^ See Osse's work previously referred to. 



- For the estimation of valerianic acid, see Zavatti and Sestini, Zeitschr. f. 

 anal. Chemie, viii. 388, 1869. 



