154 



NOTE UPON THE EXTRACTION OF ACIDS FROM CULTURES. 

 By R. Greig-Smith, D.Sf., Macleay Bacteriologlst to thk Society. 



In testing the proilucts ol' the tVrmeutatiun o£ dextrose by a rthu yeast, sue- 

 cinic aeid was obtained as tlie only ti.xed acid, but during its separation, several 

 observations were made which may be of interest. 



The fermented fluids are usually evaporated in neutral or alkaline solution, 

 generally in the presence of an excess of calcium carbonate and when the liquid 

 is siilliciently reduced, it is cooled and the lime salts decomposed with suli)lmrie 

 acid, after which the calcium sulphate is i-emovcd by filtration and the volatile 

 acids removed in a current of steam. 



The residual fixed acids are then evaporated until of sufficient consistency to 



be extracted with ether. There may be, and usually is, a ijuantity of sugar in 



the liquid which prevents the evaporation being pushed to a limit, say, of 20 c.c. 



or which does not give a tractable dry powder when mixed with sand. In such 



cases one has to work with a volume of licjuid mea.suriiig possibly 100 c.c. Witli 



this volume, the extraction is slower than is generally considered. For example, 



Schoorl (through .Journ. Soc. Chem. Ind., xix.. I'JOO. .5()7), when working with 



pure acids, found that succinic, lactic and oxalic acids were extracted from 20 



c.c. of liquid in 8 hours. The time may be longer in the presence of much sugar 



and nitrogenous substances, but this has not been investigateil. Schoorl state.s 



that the time of extraction depends upon tlic iiartition e(|uivalciit. wliich is the 



solubility of the acid in water. 



— , I .|.^' — ^7—, rrr-. -; An acid such as succinic with a hiw cocllicicMt 



solubility of the acid in ether. 



fakes a short time, and one with a high coelHcient such as tartaric acid takes a 



long time. He gives the coelHcients as succinic, 4; oxalic, 8; lactic, infinity; 



malic, 24; citric, 5!); and tartaric, 330. In extracting unknown acids as. for 



example, in a bacterial culture, one naturally continues tlie extractions until 



little (iP 11(1 resi(hie is obtained ujxin evaporating the ether frdiii a thr('<' hours' 



extraction. 



More recently Pinnow (Jour. Soc. Ciiem. Ind.. xxx\-., lOKi. HIT) determined 



tlie coefficients of distribution between cerfain organic acids in water and iu 



ether and compared the speed of their extraction by ether in a Parthiel-Rose 



extraction ai)paratiis. He found fliaf tlie extraction practically followed the 



formula for monomolecular reactions and, within certain limits, was inversely 



proportional to the volume of li<]uid extracted and to the distribution coellicienf. 



His coefficients at 27° are for suci'inic acid, 7..58; lactic, 11.28; oxalic, 13.9; 



