i86 



weighing, of bacterial substance, whereas the other half was titrated with kalium- 

 permanganate. We used for this a three months old culture on: 



Tap-water 100 



Na.-HPO. 0.02 



KC1 0.02 



KNOs 0.02 



The film from the part, destined for the weighing, was separated from the liquid 

 by filtration, washed out on the filter with strongly diluted hydrochloric acid, and 

 subsequently with distilled water, to remove the chlorids. Subsequently the filter with 

 the film was dried, first at 40 50 C. and then at iooC., until the weight remained 

 constant. So we found that per litre 180 milligrams of bacterial matter were pro- 

 duced, and that, after deduction of 14 milligrams, used by a litre of our tap-water it- 

 self, the corresponding permanganate number was 94. We can thus, with an accuracy 

 sufficient for our purpose, accept that the relation between the two figures is as 2 : i, 

 that is to say, that the doubling of the permanganate number gives the weight of the 

 dry bacterial substance, and, as this latter number is much more quickly to be found 

 than the weight, we have contented ourselves with it in most our further deter- 

 minations. 



We shall now give some more figures. Like the preceding they all relate 10 

 bacterial films produced in E r 1 en m e y e r-flasks on ioocM 3 . liquid with a free 

 liquid-surface of about 80 cM 2 . 



By weighing we found in one case on: 



Tap- water 100 



KC1 0.02 



KNOi 0.02 



KsHPO, 0.04 



after 5 month's culture 235 milligrams per litre. On: 



Distilled water 100 



KC1 0.02 



KNO.s o.i 



K 2 HPO4 0.02 



Mineral solution* i drop 



after 5 months 220 milligrams per litre. 



Some numbers, found by the permanganate method follow, and in the first place 

 some relating to tap-water. 



The greatest production which we had, was obtained with tap-water 0.02 K 2 HPO 4 

 and 0.02 KNO 3) after a year's culture and amounted to 250 mgrs. of permanganate 

 per litre, nearly corresponding with 250 X 2 = 500 milligrams of dry bacterial sub- 

 stance. 



After a shorter time the production is likewise smaller; so we found in a cul- 



Tap water 100 



Na-'HPCU o.o j 



KC1 0.02 



KNOs 0.02 



after 5 month's culture (January to May) 202 mgrs. of permanganate, corresponding 

 with 404 mgrs. of bacterial matter per litre. 



