g 6 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
These analyses, as formerly, give parts per 100,000 of the water, 
and show that the water supplied by the new filter is, as already 
stated, slightly purer than that supplied by the old filter. The 
excessively high free ammonia of December—see Table III.—has 
disappeared, and this bears out Doch and Barr s contention that the 
greatest danger to a water supply, such as ours, occurs in the early 
stages of flooding, and disappears as the banks of the streams and 
river get washed free of their impurities, and, as the fine filtering 
deposit on the surface of our filter beds, which is stirred up .at the 
early stages of flooding, gets settled down again. The albumenoid 
ammonia is quite as high in these analyses as in the December 
analyses, and certainly much higher than in the mean summer 
analyses. 
We cannot here too strongly emphasise the fact that our work 
has been done quite independently as scientists—not as partisans 
for or against the Perth water supply—for the scientific society to 
which it was communicated, and at the request, publicly made, of 
some of the leading members of that society. As both our summer 
and winter analyses are entirely confirmed by an outside analyst of 
undoubted repute, we can guarantee their accuracy, and in no case 
is the filtered water condemned. The analyses do prove that the 
water changes, in regard to the amount of ammonia present, more 
than a natural water should, and our whole contention is that water 
with fresh sewage matter run in immediately before filtration cannot 
possibly be acquitted by chemical analyses alone,—see Dr. Barr’s 
Government Report of the Tees Water, already referred to. In the 
summer-time, when the river is low and the purifying agents most 
active, we feel there is little to fear; but immediately after heavy 
flooding there is certainly need for caution, and this is the conclusion 
which will, we feel sure, be reached by every one able to understand 
the points at issue. 
Our thanks are here gratefully tendered to Mr. Wm. Ellison for 
making boxes for the Winchesters used in collecting the samples, and 
also for assistance with the collection of samples; to ISIr. Jardine for 
making a duplicate analysis for chlorine and hardness in a number of 
the samples of the second table; to ^Ir. Pullar and the teachers 
attending the Saturday Classes, for assistance in collecting samples; 
and also to ^Ir. Young, civil engineer, and to IMr. Mackay, chief 
sanitary inspector of the county, for copies of reports. 
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