162. Apvrnry—Unrecognised Factors in the Transmission of Gases through Water. 
After the gases in solution and in the air-spaces had been abstracted, the corks 
closing the upper ends of the tubes were removed; and the tubes for most of the 
experiments were immersed to a depth of about 1300 mm. in a large water-jacket, 
which was kept cool by a constant flow through it of water from the main supply. 
The object of the water-jacket was to prevent the formation of downward 
convection currents, by keeping the lower portions of the water-columns in the 
tubes at a slightly lower temperature than the upper portions, which were 
exposed to the temperature of the laboratory. 
In most of the experiments to be described, the surfaces of the water-columns 
were kept constantly agitated by means of currents of air drawn through their 
upper layers. or the few preliminary experiments to be described, the tubes 
were fitted with corks carrying fine glass inlet and exit tubes of 3 mm. bore, 
and for the later experiments with glass capillary tubes of 0°5 mm. bore. The 
inlet tubes dipped at different depths, from 10 to 200 mm., below the surface. 
Slow currents of air were employed, at the rate of about 1000 cc. per hour, 
with the smaller bore inlet tubes, and at somewhat quicker rates with the tubes 
of the larger bore. 
In a few cases the surfaces of the water-columns were agitated by mechanically- 
rotated glass stirrers, just dipping below the surface of the water. In these cases, 
the experimental tube employed was of wider bore to allow of stirrers of a gridiron 
shape being used. 
When the surfaces of the water-columns were left unbroken, the experimental 
tubes were loosely covered to protect their contents from dust. 
The height of the columns of water was in nearly all experiments about 
1800 mm. In all experiments the surface of the water was freely exposed to the 
air. Observations of barometric pressures were not thought necessary. 
At the conclusion of each experiment, layers of the water of 100 to 200 mm. 
thickness were drawn from different depths from the surface, and stored in tubes 
standing over mercury until they could be analysed. 
The dissolved gases in these samples were extracted by boiling with a little 
sulphuric acid in vacuo. The apparatus employed for this purpose, and for the 
analysis of the gases, has already been described by the author in his memoir on 
dissolved gases and fermentative changes.* 
Of the results of the analysis of the dissolved gases, only those for the nitrogen 
are recorded in this communication. These are expressed in ce. at 0°C. and 
760 mm. bar. 
* Trans. Royal Dublin Society, 1895, vol. v., Part x1. ; ‘‘The Course and Nature of Fermentative Changes 
in Natural and Polluted Waters, and in artificial Solutions, as indicated by the Composition of the dissolved 
Gases,” 
