680 PROCEEDINGS OF SECTION I. 



remains brownish red, the liquid is usually quite inoffensive. 

 McGowan found that these two tests ran for the most part together 

 in the case of land effluents. 



Barwise carries out the incubator test by determining the 

 oxygen absorbed in three minutes before and after incubating at 

 80°F. for a week. He makes no suggestion with reference to 

 determination or influence of nitrites. He apparently follows the 

 practice laid down at the Manchester inquiry in 1899. 



The Committee of the American Public Health Association, 

 appointed to report on Standard Methods of Water Analysis in 

 1905, lays down the following procedure : — 



" Determinations are made of the dissolved oxygen, nitrogen as nitrites 

 and nitrates, and the oxygen consumed by digestion in an acid sohition 

 with potassium permanganate at room temperature for a period of three 

 minutes. After the sample has been incubated for 24 hours or more at 37°C., 

 observations are made as to the appearance of the sample, i.e., whether it 

 has turned black or not, and particular attention is given to the presence or 

 absence of well-defined odours of putrefaction. Samples, which, after in- 

 cubation, are black in appearance and which possess foul odours, may be 

 unquestionably regarded as putrescible without making any further tests. 

 Samples, which, at the end of the incubation period still contain an appre- 

 ciable quantity of dissolved oxygen or oxygen available from the nitrates, 

 and are free from sulphuretted hydrogen or other odours resulting from 

 putrefaction, may be generally regarded with safety as non-putrescible. 

 Samples in which dissolved oxygen and nitrogen in the form of nitrates are 

 absent or nearly so, with more or less nitrogen in the form of nitrites, and in 

 which the oxygen consumed in three minutes is increased on incubation, 

 require more careful consideration before regarding definitely the result of 

 the putrescibility test. The best procedures by which anj^ additional in- 

 formation can be obtained appear to vary under different local conditions 

 as to character of sewage treated, method of treatment, season of the year, 

 etc., and it seems inadvisable now to specify in precise terms further pro- 

 cedures for use under all circumstances. As the applicability of this test 

 is studied in various laboratories, it is recommended that reports set forth 

 procedures l)y which conclusions ha\'e been arri\-ed at with reference to 

 putrescibiHty." 



Stoddart, Dunbar and Thumm determine putrefaction by the 

 presence of sulphuretted h5'drogen. Adeney carried out the test 

 by mixing the effluent with water from the stream into which it is 

 proposed to discharge the same, in the proportion of their relative 

 flows. 



An exhaustive study of the whole subject of putrescibility has 

 recently been made by Johnson, Copeland, and Kimberly.^ These 

 investigators endeavour to find a relation between the putrescibility 

 or stability of tm effluent and its chemical analysis, particularly the 

 oxygen consumed figures on one hand representing oxidizable 

 material and the available oxygen in the form of free oxygen, 

 nitrates and nitrites on the other hand. The data required in 

 establishing such a relation are :■ — (1) The available oxygen in the 

 form of free oxygen, nitrates and nitrites, and (2) the consumed 



J Journal Infectious Diseases, 1906, Sept. II., p.80. 



