of Edinburgh, Session 1871 - 72 . 551 
days it lost only 0'42 grain in weight, and crystals of carbonate of 
lead were deposited scantily. In circumstances exactly the same, 
distilled water will form carbonate of lead in abundance, and the 
loss of lead is 34 grains, or eight times as much. 
In times of flood the condition of the water in such streamlets 
necessarily undergoes change. But the difference is not so great 
as might naturally be expected. In the night of 19th September 
last and subsequent morning rain fell steadily at Loch Goil, and 
heavily for twelve hours; and, consequently, in the forenoon of 
the 20th the streamlet described above was considerably flooded. 
The water, seen in bulk, was somewhat brownish ; it was even 
faintly brownish in a dining-room water-bottle ; and in a 16-inch 
glass tube it appeared yellowish. Nevertheless, it looked well 
enough in a glass tumbler, and it was not in the slightest degree 
turbid. Its purity, apart from its colour, was very great. No 
liquid test for inorganic salts hut one, — not oxalate of ammonia, 
not nitrate of silver, not even acetate of lead, had any visible effect. 
The soap-test alone exerted any manifest action ; and this indicated 
only 0*8 degrees of hardness, which is equivalent to little more 
than an 80,000th of carbonate of lime in the water. In corre- 
spondence with this condition, lead underwent rapid corrosion in it. 
A plate, an inch and a half square, lost in twenty-eight days 3’09 
grains in weight, or about -J-f ths of the loss in distilled water in 
the same time ; and crystals of carbonate of lead were formed in 
abundance. 
I examined the same stream on a previous occasion after a furi- 
ous tempest and rain-flood on the 24th August last. Much rain 
had fallen at Loch Goil previously for several days. But on the 
24th it fell in torrents, and for half-an-hour that forenoon like a 
tropical deluge. During this period a great extent of grassy turf 
was torn off in the upper part of the stream, probably by a water- 
spout. In a few minutes the streamlet, already in high flood, 
became a muddy tumultuous torrent in which no man could have 
stood or lived ; swiftly its muddy waters spread out over the salt 
water of Loch Goil ; and then meeting similar floods first at its 
own side, and afterwards from the opposite shore, the united muddy 
torrents covered the whole upper reach of the loch in less than 
half-an-hour to the extent of two miles in length, and three-quarters 
