ACID FERMENTATIONS. 359 



observed by WEIIMER (XXVIII.), more particularly in the case of 

 Citromijces Pfejferianus and Citr. glaber. According to the same 

 worker (XXIX.), both Penicillium luteum and Mucor piriformis 

 are feeble acid-formers. 



Being an oxidation fermentation, the process is dependent on 

 the presence of an abundance of oxygen, in the same degree as 

 the acetic and oxalic acid fermentations. When air is excluded, 

 neither Aspergillus nor Citromyces spores will develop at all, and 

 even the mature growths only survive a short time under these 

 conditions. Although citric acid must also be regarded as the 

 product of an incomplete oxidation, its formation is not the 

 result of an insufficient supply of oxygen, but the consequence 

 of a decomposition arrested through other causes. True, the 

 temperature does not seem to be such a decisive factor as in 

 oxalic acid fermentation, and further determinations are necessary 

 in order to elucidate the dependence of the process on external 

 conditions. In this case also the chemical character of the 

 organic nutriment is an essential factor, carbohydrates or allied 

 substances alone, and not peptones, amides, salts of organic acids, 

 &c., enabling the production of free acid to take place. 



In its incipient stage, the acidification, which takes place with- 

 out any visible liberation of gas, can be detected by the blue 

 reaction with Congo paper ; and an addition of chalk produces 

 brisk effervescence. The acidity gradually increases, the limit 

 being reached at about 8 per cent., without any apparent in- 

 fluence on the development of the fungus. The latter then 

 begins to redecompose the accumulated acid, and the acidity 

 decreases, no trace of free acid being perceptible at the end of a 

 few weeks longer ; hence it is undoubtedly merely an inter- 

 mediate product that has momentarily escaped further decomposi- 

 tion. In this case, also, the anticipated effect of fixing the acid 

 in the form of salts is realised, neutralisation preserving the acid 

 from redecomposition ; at the same time the formation of acid is 

 accelerated and the total amount is considerably increased. Con- 

 sequently, whilst the acidity increases but slowly in the absence 

 of chalk, the addition of this substance to the acidifying culture 

 results in a continuous liberation of gas, much more apparent 

 than in the case of oxalic acid fermentation, and followed in a 

 short time by an extensive deposition of calcium citrate. 



The citrate is separated from the unaltered calcium carbonate 

 by dissolving it in hydrochloric acid, neutralisation with ammonia, 

 and boiling which precipitates the citrate the mass being dried 

 at 110 C. and weighed, so that the quantitative yield can be 

 approximately determined. The average weight is from one- 

 third to one-half the quantity of sugar, in the form of the 

 crystallised acid (with i molecule of water), this being recovered 

 in the usual manner by freeing it from the lime salt with sul- 

 phuric acid, filtering from the resulting gypsum, and concentrat- 

 ing to the point of crystallisation. Hence, in well-conducted 



