NATURAL HISTORY OF THE BANKS OF THE TAY. 
95 
sufficiently pure for all purposes, and even at its worst sufficiently 
pure to pass a chemical analysis respectably, but Koch’s second 
paper and Dr. Barry’s report conclusively prove that after flooding, 
frost, or any other derangement of the filters, such water is apt to be 
more or less contaminated and in a condition such as to induce or carry 
disease all over the area in which it is used. The last table of analyses 
goes to prove that Perth water at least deteriorates during the winter 
months, and we are strongly of opinion that at such times especially, 
a strict bacteriological examination is also indispensable along with the 
chemical analysis. In water once contaminated with sewage, chemi¬ 
cal analysis alone is undoubtedly not sufficiently refined to detect 
pathogenic bacteria, or to prove the water innocuous. This is shown 
beyond doubt in the case of the Tees water, which from chemical 
analyses, was reported by such experts as Dr. Frankland and Mr. 
Allen to be “ free from every trace of previous sewage or animal con¬ 
tamination.” 
Boiling, of course, destroys these pathogenic bacteria, and for 
nearly two years we have used none of the Perth water for drinking 
purposes without first boiling it, and the result has been such as to 
give us confidence in recommending the same course to others. 
A few days after the above paper was read to the Society a gentle¬ 
man who had been actively connected with the Perth Water Supply 
wrote suggesting that the increase of impurity in the winter months 
was due to the new supply from above the Bridge, and in order to 
test that we obtained, through the kindness of the Lord Provost and 
the Water Commissioners, samples from the old and new filters 
separately at the water-house. One of these samples was sent to 
the City Analyst from Blairgowrie, and the others were analysed in 
our own Laboratory, the result being as follows :— 
TABLE IV.-ANALYSES OF PERTH WATER SUPPLY, JAN. 16th, 1894. 
(river in FLOOD.) 
I. 
II. 
III. 
IV. 
Old 
Supply. 
New 
Supply. 
From Service 
Pipe. 
Confirmatory 
Analysis 
of I. 
Solids, Organic Matter, 
7 
7 
•5 
*5 
,, Volatile ,, 
2 'I 
1*8 
2*4 
} 
,, Saline ,, 
- 3-2 
2*4 
3-0 
,, Total ,, 
6’o 
4’9 
5*9 
4-8 
Chlorine, - 
I'O 
•8 
*9 
(not given) 
Ammonia, Free, 
,, Albumenoid, 
- *002 
•002 
'002 
•0043 
- -0075 
•007 
•007 
•0071 
,, Total, 
- -0095 
•009 
•009 
•0114 
Hardness, Temporary, 
- ‘35 
•3 
•3 
*57 
,, Permanent, 
- 2'90 
27 
2*9 
2.86 
,, Total, 
- 3'25 
3-0 
3-2 
3*43 
