146 Proceedings of Royal Society of Edinburgh. [sess. 
was closed above with a piece of rubber tubing firmly clamped. 
The opposite stopper was bored for a small glass tube passing to 
within an inch of the bottom, and closed above by a piece of rubber 
tubing securely clamped, and served for the removal of samples of 
the water. This stopper also carried a thermometer. The central 
stopper was fitted with a short piece of tubing connected with a 
cylinder of nitrogen. 
Procedure. — The bottle was completely filled with nearly boiling 
water from the tap, the stoppers were securely put in, and the 
water was driven out of the first opening by a stream of nitrogen 
through the central tube till about 2500 cc. were left. This was 
allowed to stand all night, and next morning the oxygen generally 
amounted to 3 cc. per litre. 
In this, rainbow trout of about nine months old, weighing from 
1'5 to 5 grms., were introduced. For these I am indebted to Mr 
Armistead, of the Solway Fishery Company. Water for analyses 
was taken by connecting a 50 cc. pipette with the small rubber 
tube in the small glass tube, and forcing up the water by allowing 
nitrogen to pass from the cylinder into the bottle. 
A control observation was generally made by keeping fish in a 
flask of tap water 
For the determination of the dissolved oxygen Professor 
Ramsay’s method was used ( Journal of the Society of Chemical 
Industry , 30th Nov. 1901). The method is a rough one, but it was 
found to be sufficiently accurate for the present inquiry in the 
hands of one accustomed to use it. The standards had been 
checked at University College, London, just before this series of 
observations were made. 
Experiments. 
Experiment I . — A mixture of a number of samples of water sent 
from the Tyne Estuary was made, and divided into two equal 
parts. One was left standing for two days without agitation, and 
the other was frequently shaken with air. On the second day 
the former contained no oxygen detectable by Ramsay’s method ; 
the latter, immediately after agitation, 4 cc. per litre (on standing 
for a few hours this fell markedly). 
Tap water was boiled vigorously, and as it cooled, siphoned 
