of Edinburgh, Session 1871 - 72 . 
557 
although the colour is the same at the bottom as at the surface, 
and very slight, it is distinctly deeper in shade when seen in a 
16-inch tube; and the film left on evaporation, instead of being 
light grey, is of a rather deep yellowish -brown tint. 
[ May 16 th, 1872. — As supplementary to these observations, I 
may here add the following, which I had an opportunity of mak- 
ing on the 10th of last month : — During the five winter months 
intermediate between my previous visit in November, the winter 
had been unusually open. Until the middle of March, indeed, there 
had been very little frost, and no severe cold. During the latter 
half of March frosty northerly winds prevailed, but without any very 
great fall of the thermometer. In the last days of March and first 
three days of April, snow fell frequently, covering the Highland 
mountains to their bases. Ben Lomond and the adjacent Arrochar 
mountains shared in the change. On 4th April the wind veered 
to west and south-west; bright sunshine and warmth soon dis- 
solved most of the snow, and this weather continued, with scarcely 
any rain, till after my visit. The ground around Loch Lomond 
was consequently dry, the hill streams very low, and the streamlets 
dried up, or nearly so. 
The surface water corresponded with these antecedent circum- 
stances. Frequent winter floods had swept from the mountains 
most of the soluble matter from their beds ; and for some days the 
streams, reduced to rills, would have little remaining to remove 
from their stony channels. Hence the surface water was of great 
purity. A white porcelain basin, two inches in diameter, was 
visible at the depth of 16 feet, although a light breeze rippled the 
surface. In a 16-inch tube the yellowish colour was extremely 
faint. The solid contents amounted to only a 32,000th of the water, 
and lost a fourth by incineration.* Nitrate of silver occasioned 
in the water only the faintest haze, and oxalate of ammonia did 
not visibly affect it. The soap-test indicated 0 - 49 of hardness, 
which is equivalent to a 145,000th of carbonate of lime. In accord- 
ance with its purity this water acted powerfully on lead. Action 
commenced at once, loose crystals of carbonate of lead were formed 
* 26,250 grains left 0'83 at 300° F., and 0 62 after incineration. 
