60 
Proceedings of the Royal Society 
sufficient to bring its temperature of maximum density down from 
39 *2° to about 37°. Three or four parts of common salt dissolved in 
one thousand parts of the water would be sufficient to produce this 
effect, and it did not seem extravagant to look upon this as the 
probable solution of the problem, especially as the loch is the 
receptacle for the whole sewage of the town of Linlithgow^ and the 
refuse of several works. Accordingly, on the 20th January, a 
sample of water was drawn from a depth of ten feet below the ice 
at Station No. 5, and examined. My supposition appeared likely 
to be confirmed by the overpoweringly horrible stench emitted by 
the water, which argued an amount of pollution not inconsistent 
with a large quantity of dissolved saline matter. On examination, 
however, it was found to be otherwise. 
When freshly drawn the water was clear, but had become slightly 
turbid by the time it reached the laboratory ; this turbidity disap- 
peared on diluting the water with a large quantity of alcohol. It 
reacted neutral to test-papers. Its specific gravity was 1 ‘00035 at 
39 ‘9° F., that of distilled water, at the same temperature, being 
unity. 
The smell of the water was removed by boiling. Neither sulphate 
of copper nor alkaline acetate of lead solutions produced any pre- 
cipitate of sulphides. 
Finally, the water contained only 0‘03 grammes chlorine in a 
litre, and was evidently remarkably free from saline ingredients. 
It remains to determine by experiment the actual temperature at 
which this water attains a maximum density, and also, by observa- 
tions in other lochs, whether a similar distribution of temperature is 
to be found. 
Considering the excessively foul state of the loch, and especially 
of the mud at the bottom of the western part, the evolution of heat 
cannot be wondered at. 
It will be seen from the tajble that the observations made at 
No. 2 on the 9th agree substantially with those made at No. 4 on 
the 1 1 til January. At Stations Nos. 1 and 3 the depth of the 
water is nearly identical, but the temperatures at the same depths 
are different. At No. 1 the water near the surface is colder, and 
that near the bottom warmer than at No. 2. At No. 1 the tem- 
perature of the mud was not observed, but it would no doubt be 
