Formates by B. coli communis. 



469 



D, including the volume of the pressure tubing connecting A and B, having 

 been previously determined, the total volume of evolved gases may be 

 measured by raising the reservoir C, E being open, and D turned to connect 

 A and B ; the mercury then rises in B and- falls in A, in which it is allowed 

 to fall to the level L". To correct for pressure an allowance may be made 

 for the height of the mercury from the surface of the reservoir U" to L", 

 but it is also quite convenient to lower the whole Liebig's condenser until 

 L" coincides with L"'. The volume of gases in the graduated tube B is 

 then observed, and this volume added to that of the inner tube A. A sample 

 of the gases may now be conveniently removed by lowering C. When B 

 contains sufficient of the gases for analysis, the whole apparatus B-C may, 

 if desired, be removed from its connection with A. 



The apparatus has been described in detail because it is of use for the 

 determination of all gases remaining in the fermentation flask. In the 

 experiments recorded in the present communication, however, it was only of 

 value to determine residual carbon dioxide. 



Details of the Determinations. — The carbon dioxide boiled off from the 

 solution, as described above, is measured in the usual way. The flask is 

 now detached from the apparatus and the contents filtered from the deposit 

 of chalk, and the filtrate and washings precipitated in hot solution with 

 ammonium oxalate. The precipitate of calcium oxalate is used to estimate the 

 calcium corresponding to the total acids produced during the fermentation, 

 an allowance being made for the calcium in the peptone. The filtrate from 

 the calcium oxalate is acidified with oxalic acid and distilled in steam, the 

 distillate neutralised with deci-normal potash and evaporated to dryness ; 

 the residue is dissolved in about 50 c.c. of water, and the formic acid 

 determined by the reduction of mercuric chloride. The residue from the 

 steam distillation is made up to a definite volume, and an aliquot portion 

 used for the determination of the residual sugar by Bertrand's method after 

 the removal of peptone by Patein's mercuric nitrate reagent. 



The results of the experiment are summarised in Table III. 



It will be seen from Table III that about ten times as much gas was 

 produced by the selected strain of B. coli communis from calcium formate in 

 the presence of glucose as was produced by it from calcium formate alone. 

 The amount of sugar decomposed in the presence of calcium formate is 

 considerably greater than in its absence, even when the medium is kept as 

 far as possible neutral by chalk. 



