PROCEEDINGS OF SECTION I. 



681 



to me to be altogether practicable, because, at room temperature, at 

 all events, the nitrites are not fully oxidised at the end of three minutes. 

 Fowler recommends the destruction of nitrites \)y the addition of urea 

 after the sulphuric acid. This I have not tried. 



In view of the irregularities caused by the presence of nitrites, 

 and, further, in view of probable confusion from the test made in this 

 way, it seems to me that full value can be secured by the observance 

 of the physical conditions after incubation, and that chemical examina- 

 tion, as indicated above, is superfluous. The test of itself is undoubtedly 

 of value, but the results are capable of more accurate interpretation 

 by the simpler methods of direct observation than by the more com- 

 plicated chemical tests recommended. By its application in the way 

 I suggest it becomes available for more extended use by persons not 

 skilled in chemical procedure. 



The full results of the incubator tests, together with the changes 

 in the nitrites, are given in the following table : — 



Note. — Parts by weight per 100,000. * Small amounts not estimated. 



+ No test made. 



As to the source of nitrites after incubation, I have reason to 

 believe that they are due to the reduction of nitrates. In several 

 instances where the amount of nitrates was estimated it was found 

 that there had been a proportional diminution. The reduction was 

 probably, to a large extent, effected by bacteria, for it is well known 

 that in the absence of free oxygen many bacteria possess a faculty of 



