238 - THE PHENOMENA OF PUTREFACTION 



tinuity of the nitrogen cycle, is the task of a separate group of bacteria, which 

 will be dealt with in chapter xxxiii. 



The reduction of nitric acid by bacteria does not always stop short at the 

 liberation of free nitrogen, but in many instances extends to the formation of 

 ammonia. Several investigations on this point were made by 0. LOEW (III.)> 

 but, unfortunately, not with pure cultures. He found that " ordinary putre- 

 factive bacteria," grown in a solution of i per cent, of peptone, 0.2 per cent, of 

 KN0 3 , and 0.2 per cent, of K 2 HPO 4 , cause the potash and carbon dioxide to 

 combine, whereas the nitrogen of the nitric acid is converted into ammonium 

 carbonate. When 0.2 per cent, of ethyl alcohol is also present (in anaerobic 

 cultures) the acetate is formed instead of the carbonate. 



What has already been detailed will explain the so-called nitric fermentation 

 of molasses. The cell sap of the sugar-beet contains a quantity generally 

 small, but occasionally larger of nitrates, principally potassium nitrate. This 

 is not separated during the saturation process, but remains in the mass in un- 

 diminished quantity, a portion crystallising out, and being then found in the raw 

 sugar from the centrifugal machine, whilst the rest remains in the mother liquor, 

 i.e. the separated syrup. If this syrup is then boiled up for the manufacture of 

 second product, and again passed through the centrifugal machine, the proportion 

 of nitrates in the mass will be still larger, Pellet having found 1.9 per cent, of 

 KN0 3 in one sample examined by him. At this stage the molasses has a faintly 

 alkaline reaction, and is rich in organic and inorganic nutrient substances of 

 various kinds. Hence it is no wonder if bacteria rapidly develop therein. 

 Under special conditions the upper hand is gained by such organisms as reduce 

 potassium nitrate and eject its nitrogen in the form of NO, which compound, on 

 coming in contact with air, is oxidised into the dioxide N0 2 . The latter hangs 

 as a dense red-brown vapour over the surface of the molasses, and the sugar- 

 maker then says his molasses is in a state of nitric fermentation. This pheno- 

 menon is of less frequent occurrence in the "reserves" in the sugar-factories 

 than in the dilute molasses of the molasses distilleries. Certainly, the activity 

 of these reducing bacteria can be arrested by souring, but this treatment liberates 

 organic acids inimical to the yeast. Bearing this in mind, Czeczetka proposed to 

 remedy the evil by boiling the molasses directly the malady is observed. 

 According to a report by DUBRUNFAUT (I.) in 1868, nitric fermentation was first 

 noticed by Tilloy at his distillery in Dijon, and was successfully suppressed by 

 him by boiling the molasses along with sulphuric acid. An explanation (charac- 

 teristic of the state of knowledge in the domain of Fermentation Physiology at 

 that time) of the favourable influence of this treatment was made in the same 

 year by J. REISET (II.), who stated that the NO or N0 2 formed during the so- 

 called nitric fermentation proceeds from the oxidation of ammonia in the 

 molasses, this being attacked only when present in combination with a weak acid, 

 whilst when in the form of sulphate it resists the action of oxygen ; consequently 

 the molasses treated in the manner adopted by Tilloy was exempt from this 

 decomposition. This view was left uncontradicted by BKCHAMP (III.), although 

 he had already ascribed de-nitrification to the agency of micro-organisms. A 

 closer investigation (embodying modern methods of working) of this nitric 

 fermentation of molasses is highly desirable. To be thoroughly satisfactory, 

 such research must trace the course followed by the potassium nitrate in the 

 juices of the sugar- works, and more narrowly examine the quantitative dependence 

 of the nitrate in molasses on the method of preparation employed, very little 

 being as yet known on these points. 



The nitric decomposition in question is also of frequent occurrence in the 

 fermentation of tobacco in heaps. SCHLOSINO (III.) reported in 1868 on the 

 first observation of this phenomenon by Ch. Ray. 



