559 
of Edinburgh, Session 1871 - 72 . 
was found by microscopical examination to abound in diatoms and 
skeleton tissues of graminaceous and other vegetables. The bottom 
water contained a 25,000th of solids. 
It has been proposed, in projects for introducing lake water into 
a town for domestic uses, to draw the water from a considerable 
depth, instead of from the surface, under the supposition that the 
deep water is the purest. The preceding observations show that 
this is a mistake, at least in the case of some lakes. On every occa- 
sion I have found the water of Loch Lomond somewhat more saline 
in its deepest parts than at the surface immediately above, and 
decidedly more coloured. The cause is easily understood, if the 
preceding chemical examination be taken in connection with the 
observations to be subsequently made on the temperature of Loch 
Lomond at various depths. For the results of both inquiries con- 
cur in indicating that, in the very deep parts, there is a vast body 
of still water which undergoes little, or, perhaps, no change or 
movement, and which, therefore, at the bottom, will become impreg- 
nated with whatever is soluble in the bed on which it rests. 
Let me now change the scene to the hills and the waters of the 
Lowlands. 
In the course of late notorious proceedings in this city for obtain- 
ing a more abundant water supply, it was stated by good chemical 
authorities that the water of St Mary’s Loch in Selkirkshire, 
although of remarkable purity, does not exert upon metallic lead 
that eroding action which is a singular property of all pure waters 
previously subjected to trial. This statement was so opposed to 
the principles regulating the action of waters upon lead, as pro- 
pounded by me so long ago as 1829, and also to the facts brought 
forward both then and in a paper read to this Society in 1842, 
that I resolved to investigate the question for myself. 
This undertaking, in spite of my strong repugnance and steady 
refusal to be involved on either side of the Edinburgh water-con- 
troversy, led indirectly to my being compelled to concern myself 
with it as a parliamentary witness. But let it be clearly understood 
and it was never used except for these experiments. The cistern was emptied 
at once into stoppered bottles on being drawn into the boat, and was carefully 
dried in a current of air with the valves open. 
