190 
the gas rising near Barton often contains nearly 60 per cent 
of “marsh gas/’ the rest being mostly carbon dioxide. The 
river water is nearly saturated with carbon dioxide gas (at the 
atmospheric temperature), a very bad state of things, because 
it prevents to a very great extent that further special self- 
purification of the water by oxydation. The carbon dioxide 
is mostly formed by the oxydation of the sewage and other 
carbonaceous contaminations present in the water. I have 
made a great number of determinations of the amount of 
free carbon dioxide gas in solution, in the Irwell water, and 
always found that on allowing the same water sample to 
stand for a week (or even a day or two in summer), that a 
further amount of carbon dioxide had been formed and 
dissolved in the water. This further amount was entirely 
derived, from the oxydation of the carbonaceous impurities 
of the water. I ascertained on making further experiments 
that an increase of temperature had a very great influence 
upon the formation of carbon dioxide in sewage polluted 
water. The way I ascertained this was very simple. I first 
determined very carefully the amount of free carbonic acid 
gas (carbon dioxide) dissolved in the Irwell water, by gently 
warming it in a flask to about 94°C., and drawing all gas 
evolved through a standard solution of Barium-hydrate. 
When no further amount of gas was thought to be coming 
off, the barium-hydrate flask was removed and the amount 
of baryta still remaining not saturated determined by 
standard oxalic acid solution; then another flask containing 
a further charge of the barium-hydrate solution was attached 
to the apparatus as before, and the water sample again heated 
in its flask for half an hour at 94^0., if no more gas came off 
I at once proceeded to heat the flask to 100°C., when a copious 
generation of carbon dioxide always took place. If the 
carbon dioxide came off during the second heating to 94°C., 
then this heating was continued for a considerable time 
