360 CHEMICAL ACTIVITY OF ASPERGILLACE^E. 



experiments, nearly half the sugar is converted into citric acid, 

 without any appreciable hindrance to the development of the 

 fungus. As we have seen, Asp. niger is also able to transform 

 about one-half the sugar (dextrose) into oxalic acid, the resulting 

 weight of acid being more than three-quarters that of the original 

 sugar. 



C 6 H 18 6 + 3 . C 6 H 8 7 + 2H 2 



180 192 (+ i molecule IT 2 O = 210) 



Dextrose. Citric acid. 



6 H 12 8 + 9 = 3 r 2 H a 4 + 3 H 2 



1 80 270 (+ 2 molecules H 2 = 306) 



Dextrose. Oxalic acid. 



In both cases about one-half the material is consumed in 

 satisfying the needs of the fungus; but possibly an alteration 

 in the conditions of experiment might increase the proportion of 

 the product. The resulting calcium citrate remains at first dis- 

 solved in the culture liquid, and it is only as the concentration 

 increases that it separates out largely in the form of a bulky 

 crust, consisting of coherent acicular or granular concretions, at 

 the bottom of the vessel. When precipitated in the above 

 manner from hot solution, it has the composition (C 6 H 5 7 ) 2 Ca 3 + 

 4H 2 0, containing therefore about three-quarters of its weight of 

 crystallised acid (C 6 H 8 O 7 + H 2 0), which is recovered in a pure 

 state, free of impurities. 



With reference to the technical importance of a process of 

 this kind for manufacturing citric acid, it may be mentioned that 

 the market price of the acid is about six guineas per cwt., 

 whilst that of the raw material is only about one-tenth that 

 figure. Nevertheless, there are certain difficulties, not easily 

 overcome in practice, with respect to the nature of the apparatus 

 required for manufacturing large quantities of acid, as well as 

 in connection with the risk of infection and the fluctuating 

 character of the fermentative power. The " Fabriques de Pro- 

 duits Chimiques " at Thann and Miilhausen, under the manage- 

 ment of Scheurer-Kestner, have been occupied with this question 

 for a long time. 



The chemistry of the process also merits a brief description. 

 The conversion of sugar (dextrose) into citric acid is a matter 

 not merely of oxidation, but of the simultaneous splitting up of 

 the normal carbon chain of the sugar molecule. In accordance 

 with the formula of the acid, the one carbon atom is transferred 

 to a side chain : 



COOH COH 



CH 2 CH.OH 



COH. COOH CH.OH 



CFT 2 CH.OH 



COOH CH.OH 



Citric acid. CH 2 OH 

 Dextrose. 



