2 Mr Waldies investigations connected [No. 1, 



But if the estimation of the organic matter in waters is to be of any 

 value at all as a means of judging of their salubrity, it is essential that 

 it should be done accurately. If it is to be a fundamental datum 

 on which Municipalities are to choose or reject certain waters for the 

 supply of large towns, that sanitary boards are to draw conclusions 

 from as to the healthiness of certain localities for the residence of 

 troops or other collections of human beings, and on which medical 

 men and hygeists are to reason respecting the origin of disease or the 

 maintenance of health, it is unnecessary to say that it ought to be 

 ascertained in a reliable manner. 



In the case of my own results, differing so widely from those referred 

 to, the question occurs, is there no way of accounting for them or 

 reconciling them ? One cause has been suggested to me independent 

 of correctness of method of analysis or of accuracy in its execution, 

 namely the age of the water when examined, that is the length of 

 time which had elapsed since the water was taken from its source. 

 High chemical authority has been adduced for the necessity of setting 

 about the analysis with the least possible delay, on account of the 

 chemical changes which the water would undergo by keeping, which 

 would result in a diminution of the quantity of organic matter 

 present. The validity of the caution I am not disposed to deny, neither 

 am I prepared to deny that in my own operations this point was not 

 always sufficiently attended to. Indeed it had not particularly 

 attracted my attention ; except as regards gaseous constituents the 

 point had not been particularly noticed either in text-books or 

 monographs I had seen, and the consideration that the organic matter 

 collected by rivers had already been freely exposed to decomposing 

 agencies, so that probably what remained was not readily decomposible, 

 confirmed as this was by my own observations while operating, led 

 me not to attach much importance to it. Still it appeared that there 

 might be a change of considerable amount shortly after collection 

 which had passed unnoticed, while afterwards the water remained less 

 liable to change. A small change, experiment shewed, did occur 

 speedily, but the present question did not refer to a small change but 

 to a large one, and it was desirable if possible to ascertain to what 

 amount it might extend. The question principally concerned the 

 waters of the hot season and of the rainy season. 



