166 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



incubator at 35° C. In fifteen days, if the conditions of the 

 experiment are successfully realised, all nitrite and nitrate will 

 have disappeared : 100 c.c. of the solution are then poured off 

 and a further 100 c.c. of tap water, containing the same 

 quantities of potassium nitrate and potassium hydrogen phos- 

 phate as originally used, are added. On incubating, the nitrate 

 wiU be found to disappear much more rapidly, and on further 

 repetitions of the process Van Iterson was able to reduce 

 0'5 gram potassium nitrate in one or two days ; the paper in 

 the meanwhile disintegrates and disappears, and potassium 

 carbonate or bicarbonate is found in solution. The evolution 

 of nitrogen was observed, but no trace of hydrogen, methane 

 or nitrous oxide. The equations representing this change are 

 given by Van Iterson as follows : — 



5C0H10O5 + 24KNO3 = 24KHC03-f I2N2+6CO2+ ISH^O 

 CoHioOg + SKNOa = 4KHCO3 + 2K2CO3 + 4N2 + 3H2O 



The evolution of gas during this reaction can be demon- 

 strated, as in the case of the anaerobic decomposition of cellu- 

 lose, by attaching a flask to the end of the Hempel gas burette, 

 the flask being kept meanwhile in a constant temperature 

 water-bath. 



For the quahtative demonstration of the evolution of 

 gas in decompositions of this sort, and to obtain a rough 

 idea of its rate of evolution, it is only necessary to provide 

 the evolution flask with a suitably stoppered inlet and 

 outlet tube, the latter reaching nearly to the bottom of 

 the flask, and being bent twice at right angles. As the 

 gas is evolved, the liquid is pushed out, and can be measmied 

 from time to time, its volume obviously being equal to the 

 volume of the gas evolved. At the end of the experiment 

 the exit tube can be connected to a cyhnder of water, and 

 the gas in the original vessel drawn out by the inlet tube 

 into a Hempel burette and examined, water entering to 

 replace the gas. The arrangement has the disadvantage that 



