654 MICROBIOLOGY OF SPECIAL INDUSTRIES 



The reaction is of an oxidizing type but the exact set of chemical 

 reactions that take place is not well understood. It is not a simple 

 oxidation process because citric acid possesses a branched side chain 

 not present in the sugar molecule. For each 50 grams of dextrose 

 converted into 13.3 grams of citric acid, 10 liters of oxygen is required 

 according to Wehmer. 



C. citricus has given very high yields of acid, although C. Pfejferianus 

 and C. Glaber have also given good results. Sterigmatocystis nigra 

 also forms citric acid in dilute sugar solutions. Many forms have 

 been studied and described but in practically all cases other acids and 

 compounds than citric acid are formed, making the recovery and 

 purification of the citric acid very difficult or impossible. 



Most of the citromyces that have come to the writer's attention 

 form during the first stages of growth a cottony white mycelium. 

 This usually later turns to pale green and in time olive brown; some 

 cultures remain permanently white. Citromyces may readily be 

 mistaken for Penicillium expansum, an organism which tends to con- 

 taminate cultures of citromyces if precautions are not taken. 



It is possible that the citromyces fermentation may in time be used 

 for commercial purposes, but it is at the present time in the experimental 

 stage. 



WHITE LEAD* 



Basic acetate of lead used so extensively in paint is of finer grain 

 and better covering quality if made by the Dutch or fermentation proc- 

 ess than if made by purely chemical processes. Grids of pure lead 

 are stacked between tiers of spent tan bark; several layers of lead 

 and tan bark being built up in well-insulated rooms. Acetic acid 

 and CO2 are formed. The acid fumes rise from the heat of fermenta- 

 tion and combine with the lead plates, forming a crust of white lead. 

 Most of the lead is converted to the basic acetate. 



The exact nature of the fermentation is not well understood. It 

 is probably not of the usual "alcohol-acetic" type carried out by S. 

 ellipsoideus or S. cerevisia and Bact. aceti, but is possibly a mixed fer- 

 mentation of several types of bacteria. Various substitutes for tan 

 bark have been tried but Calif ornian manufacturers at least have found 

 the spent bark by far the most suitable material, 



* Prepared by W. V, Cruess. 



