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IX. — Distillation with Acid Water. 



In distilling vegetable substances witli water, volatile acids 

 are obtained in the distillate, but generally in such small quantities 

 (except hydrocyanic acid) that it is often impossible, especially in 

 a mixture, to recognise their nature. In order to obtain larger 

 quantities of these volatile acids, the distillation with acid water 

 is resorted to, while employing at least I kilogram of fresh 

 raw material, or larger quantities if required. 



Usually sulphuric acid is used for this purpose, although 

 phosphoric acid is preferable on account of its non-volatility, and 

 because it does not become decomposed towai-ds the end of the 

 distillation, while sulphuric acid is reduced to sulphurous acid, 

 which passes over and adulterates the distillate. The volatile 

 anorganic acids occurring in plants (hydrochloric and nitric acids) 

 are likewise obtained by distilling with sulphuric or phosphoric 

 acid, but the hydrochloric acid may easily be removed from 

 the distillate, and the presence of nitric acid is of less conseqvience. 



As the volatile acids (i.e., those volatile by the steam of water, 

 consequently not benzoic, cinnamic, oxalic, &c., acids) ai-e always 

 contained in plants as compounds soluble in water, the dis- 

 tillation of the aqueous extract is preferable to the distillation 

 of the whole vegetable substance. Prepare, therefore, first an 

 aqiieous extract by mixing the finely-comminuted substance with 

 four to six times its weight of pure water; keeping the whole for 

 one day at a gentle heat (in the tin still of Beindorf 's apparatus) ; 

 straining, pressing, adding 50 to 60 grams phosphoric acid to 

 every kilogram of the liquid; filteiing (filtering before the 

 addition of the acid would have been difficidt or impossible; 

 should it prove difiicult still, subsiding instead of filtering must 

 be resorted to) and adding a solution of sulphate of silver, as long 

 as a precipitate is produced. ■ Allow the chloride of silver to- 

 subside, filter, pour the filtrate into a glass retort, and distil two- 

 thirds by means of a good refrigerator. 



Pour the distillate into a porcelain-dish, add an adequate 

 qi^antity (for every kilogram of raw material, about 10 grams) 

 of carbonate of baryta, rubbed down to the finest powder with a 

 portion of the distillate, and evaporate under assiduoiis stirring 

 with a glass-rod on the water-bath. Any hydrocyanic acid present 

 in the disj;,illate evaporates, while tlie other volatile organic acids 

 combine with the baryta, and remain in the liquid. Should the 

 whole of the carbonate of baryta be dissolved in evaporating, a 

 fresh portion of it must be added in order to pi-event the loss of 

 volatile acids. After the liquid has reached a certain concentra- 

 tion, and is no longer of acid reaction, it is filtered, and the 

 contents of the filter are edulcorated with water. 



