Steam Distillation of Volatile Fatty Acids From a Saturated Salt Solution.

Abstract

During a study of the volatile fatty acids of stools, a method was sought for their rapid distillation. Duclaux¹ showed that each volatile fatty acid has a specific distillation rate. Fractional distillates collected from mixtures of these acids contained the acids in proportion to their concentration and their respective distillation rates. Direct distillation for the identification of volatile fatty acids is inaccurate. Dyers method of steam distillation provides a means for fairly accurate determination of the mixture of two or three acids.

Our problem was the distillation of fatty acids from filtrates of stools; the organic matter having been precipitated. The filtrates contained large amounts of inorganic salts which could be expected to disturb the distillation rates even when obtained by steam. Some advantage would be obtained by accelerating the rates of distillation of such acids as formic and acetic. Also added accuracy would be obtained in the identification of these acids if the differences in their distillation rates could be increased.

It has long been known that proprionic and butyric acids may be salted out of solution by adding sodium or calcium chloride to saturation. It was found that if steam is passed through a saturated salt solution containing a volatile acid, the rate of distillation of tihe acid is greatly accelerated. The method of procedure is as follows:

To 100 cc. of water containing from 5 to 20 cc. of a 0.1 N solution of formic, acetic or butyric acid, 70 grams of magnesium sulphate was added, 2 cc. of 50 per cent solution of sulphuric acid, to assure strong acidity. Steam was passed through the salt mixture at such a rate that ten to fifteen minutes were required to collect each 100 cc. fraction of distillate.