1908.| Agents in the Oxidation of Amorphous Carbon. 243 
per week, but it was measurable and, continuing to be demonstrable while 
the controls exhibited no trace of this gas, it was sufficient to encourage the 
further prosecution of the research and the endeavour to confirm the results 
by other means. 
A parallel series of experiments with charcoal in which 5 litres of CQo- 
freed air was drawn each morning through the research- and control-flasks 
gave similar results. In this arrangement the baryta water was contained 
in Pettenkofer tubes and titrated every seventh day. The control-flasks 
showed no trace of COs, while from the research-flasks, after-the first week, 
an average of 8 milligrammes per week was obtained during a period of 
one month. 
An explanation of this delayed result may be found in the fact that 
calcium salts are contained in the plant cells from which the charcoal was 
derived ; the calcium oxide therefore present in the charcoal would combine 
with the COs as soon as formed, and until the process of neutralisation was 
completed no CO, would be present in the stream of air. Also a sufficient 
time was required for the growth and multiplication of the bacteria. 
Determination of Calcium Carbonate. 
If the explanation given above were true, calcium carbonate. should be 
present in the inoculated flasks but absent from the controls. Therefore the 
next step taken was an endeavour to detect the presence of calcium 
carbonate among the charcoal fragments. 
A small portion of charcoal was removed from the inoculated flask and 
mounted as a microscopic slide; a weak solution of acetic acid was then run 
under the cover-shp and an evolution of bubbles was immediately seen to 
take place, while no such evolution could be observed in the charcoal from 
the controls. 
A further confirmation was found in the fact that when freshly-heated 
charcoal was moistened with water and treated with acetic acid no bubbles. 
appeared, but after exposure for some hours to an atmosphere containing COs», 
a similar treatment with acetic acid resulted in a vigorous evolution of gas. 
An objection might be raised that these bubbles were due to the 
displacement of gases included in the charcoal, and proof is wanting that 
they were in reality CO This proof was supplied by treating the charcoal 
in one of the inoculated flasks with weak hydrochloric acid, and then passing 
a stream of air-free CO, through it and then through baryta water. When 
this was done, barium carbonate was precipitated, and titration showed that 
33 milligrammes of CO2 had been evolved. 
