BY R. GREIG-SMITH. 



91 



Evolution of Carbon Dioxide from Tempered Bark. 



The behaviour of this experiment wa.s very much the same as the preceding; 

 it was started a day later. There was a greater evolution of gas, both in the 

 test and the eoutrol, which showed tliat tempered bark is undouljtedly better 

 than raw tan-bark for the production of carbon dioxide. On the tenth day 

 bacteria were found in the control and 0.3 gram of iodine was added on the 

 eleventh day, but this did not destroy the bacteria, for slopes smeared on the 

 thirteenth day grew a good crop of cells. As crystal-violet had checked the 

 bacteria in the tan-bark control, 0.5 gi-am w-as added to this control. The addi- 

 tion of the 10 c.c. of N/1 sodinmj hydrate did not have the same effect as with 

 the tan-bark from which it would seem that either too much or too little had 

 been added. As the latter seemed more likely, 5 c.c. of N/1 sodium hydrate was 

 added to each flask. This caused a fall and, as there seemed to be no likelihood 

 of further information being obtained by continuing the experiment, 10 c.c. of 

 dilute sulphuric acid (== 5 N/1) were run into each flask. The small yield of 

 CO2 following this treatment showed that all the alkali previously added had not 

 fixed any appreciable amount of carbon dioxide. 



On the whole the experiment was far from satisfactory on account of the 

 non-sterility of the bark and especially of the control. The earlier high yields 

 from the control, which were considered to result from a chemical oxidation, 

 were, in viev: of a later experiment, the product of the activity of bacteria 

 entrapped in the pores of the bark fragments. The sterilisation of the bark' is 

 an exceedingly difficult matter. 



The loose water in the control flask was found to be sterile when tested on 

 the second and fourth days, but the presence of the bacteria on the tenth day, 

 when taken in conjunction with the amount of carbon dioxide evolved during 



