92 HIGH TEMPERATURE ORGAN'ISil OF FERMENTING TAX-BARK, 



the first few days, suggests that the bacteria were actively iermentiug wliile 

 Jield in the [tores of the bark. A later experiment with tempered disinfected 

 bark yielded 82 milligrams of CO2 in three days as against 250 in this esperi- 

 Inent. 



The addition of sodium hydrate to neutralise the inhibiting acidity of the 

 bark seemed to be faulty; there was too much of the hit or miss method about 

 it and one would like to get a more definite process. Some years ago, I showed 

 that the organic matter of rotted leaf -mould could absorb alkali from solutions 

 and there was a difference in its action upon the biearbonates of the earths and 

 the hydrates. Calculating upon 100 grams of dry ash-free leaf-mould, it was 

 found that about 100 c.c, of normal alkali were taken up from the bicarbouat«.s 

 and about 450 c.c. from the hydrates. Thus there were two kinds of acidity. 

 If there are two kinds of acidity in the tau-bark, it is probable that it is the 

 kind which can decompose t!ie biearbonates that inhibits the growth of the 

 bacteria. 



More definite information regarding the base-absorbing jtower of the l)arks 

 was obtained by placing two grams of dry bark in a bottle with 150 c.c. of N/ 10 

 baryta water and testing the loss from day to day. A similar test was made 

 with magnesium bicarbonate. The numbers that follow are tlie c.c. of luiruial 

 alkali absorbed by 100 grams of the dry liai-k.* 

 Bari/ta absorbed: — 



Days 1 2 3 4 5 6 



Alley-bark 433 457 474 476 485 491 



Tan-bark 391 415 42() 433 440 448 



MagiiesiiiDi bicnrbonale abr<iiib<'(l: — 



Days 1 2 5 



Alley-hark 135 ISfi 138 



Tan-bark 52.5 70 73.5 



The amount of alkali absorbed by the tan-bark from the l)icarbonate in one 

 day is close to that w-hich was added in the fermeutation test i)y the twelfth 

 day, viz., 16.4 e.c. for 30 grams, which is equivalent to 54.7 c.c. of N/1 for 100 

 grams. This seems to be the optimum (juantity required for a good fermentation 

 because, when more was added on the sixteenth and seventeenth days, there 

 was practically no further increase in the production. 



In the first fermentation experiment with tan-bark (p. 85) the alkali added 

 was equivalent to 18.5 e.c. N/1 for 24 grams of l)ark. i.e., 77 c.c. for 100 grams. 



A second fermentation experiment was made with alley-bark. In the first 

 experiment tiie alley-bark had been heated to tiinii 104° to 200° for two 

 hours and this was not sufficient to sterilise it. In this experiment, it w:is 

 heated to 170° and in half an lioui- the temperature rose to 205°. from which 

 it slowly fell to 180° in two hours; it remained at this for anotlier liour. In 

 order to make sure that the conti'ol at least woidd be sterile. 50 c.c. of 1 % 

 mercuric chloride in 1 % sodiuui chloride were added and 50 c.c. of water were 

 put into the test flask. Each flask cotitaiiu^d 30 gram.s of alley-bark dried at 

 130°. As the barks did not wet readily, the flasks were steamed for an hour on 

 the following morning and subse(|nently remained at laboratory temperature 

 (26°) for five days when space was available in the thermostat. The fl.isks were 

 connected up and kept at 00° until .any mechanically fixed CO2 might l)c elimin- 

 ated before the test flask was seeded with bacteria. The dififcrence in the 



* The dry tan bark contained 4.42 % and the alley bark 11.74 % of ash. 



