RETTING 103 



the sugar in the pectinous compound which also contains 

 oxygen, but undissolved, hence any oxygen which they may 

 require they are able to produce for themselves. Incident- 

 ally it is interesting to note that within twenty-four hours 

 after putting the flax straw into the pond all the free 

 dissolved oxygen is used up or has disappeared ; conse- 

 quently it is assumed that only the anaerobic bacilli 

 continue to live, multiply, and carry on the work of 

 decomposition. 



It is advisable to ensure that the required bacteria are pre- 

 sent in the plant or in the water in sufficiently large numbers, 

 if the retting is to be perfectly accomplished. " Starters " 

 may be necessary to initiate or accelerate the process. (See 

 also Rossi process, where an aerobic bacillus is the retting 

 agent.) 



The propagation of the bacteria in the plant or in the water 

 is accelerated or retarded according to the temperature, 

 chemical conditions, acidity, and alkalinity of the water 

 (water containing a weak solution of acid is preferable). 



Fermentation proceeds most rapidly at given known 

 temperatures. It is checked by raising or lowering the 

 temperature above or below this standard. 



An increase in the temperature in tank and stagnant water 

 retting not only increases the bacterial activity but results 

 in an increased acidity of the water in the process ; hence a 

 constant small flow and change of water reduces or neutralizes 

 it. 



92. Experimental Work. Apropos this point, Mr. F. K. 

 Jackson stated in a lecture given at Belfast that the following 

 results had been ascertained from experiments and observa- 

 tions made at Selby. The average acidity in stagnant water 

 at 72 F. varied from 30 to 40 milligrams per litre of liquid. 

 When a flow of water per hour was admitted to replace 0*7 in. 

 depth of water in the tank, the acidity was reduced to 25 

 milligrams per litre. When the flow was increased to 2Jin. 

 per hour, the acidity fell to 10-9 milligrams per litre, and when 



