120 Mr. Waldies Investigations connected [No. 2, 



of the hot season, as regards mineral constituents, the product of the 

 Hooghly may he considered very good water. It will he compared 

 with the Calcutta tank waters afterwards. 



Organic constituents. 



The attempt made by experiments with artificial mixtures to 

 imitate the composition of the waters of the hot season, and ascertain 

 the probable amount of change in the organic matter by keeping, as 

 narrated in Part II. " Supplementary Observations," was not continued, 

 partly because all the circumstances of the case could not be imitated, 

 and partly because the plan did not seem to be considered satisfactory 

 to those who objected to the correctness of my results in this particular. 

 It appeared to be better to continue the observations, taking care to 

 avoid delay in the process for estimating the organic matter more 

 particularly. Besides, recently the objections to the correctness of my 

 results have been in a great measure withdrawn,* and it is hardly 

 necessary for me to do anything more in the way of directly answering 

 objections, as it was never my object to criticise the labours of others, 

 but simply to state my own, carefully obtained by methods of procedure 

 the most correct and reliable known, up to the present time. 



In the original paper I considered the various methods of ascertain- 

 ing the nature and amount of organic matter in water, and discussed 

 their several merits ; and a few further remarks will now be made on 

 the same subjects. The amount of organic matter by weight came 

 first in order, but I shall at present postpone it, until the plan of oxida- 

 tion by permanganate of potash has been noticed. 



This plan has come greatly into favour, chiefly I suppose from its 

 facility of application, a very valuable recommendation, provided its 

 other merits be assured. In the original paper I gave it a qualified and 

 guarded approval ; the result of numerous experiments made since 

 has not increased my estimate of its value, nor has that experience, 

 and reflection thereon, led me to concur in the generally favourable 

 estimate in which it is held. It is said " that it is not improbable that 

 " the substances most readily oxidised, are just those most likely to be 

 " injurious in their effects upon those who drink the water." This is 

 Dr. Miller's remark. Others " believe" that the most pernicious are 



* Indian Medical Gazette, Calcutta, 1st January, 1S67, p. 14. 



