on the Absorption of Air by Water, 173 



5. After five days . 



6. After six days . 



7. After seven days 



8. After eight days 



9. After nine days . 

 10. After ten days . 



On the ninth day, after analyzing the gas, I dissolved 

 some sulphate of iron in the water-trough. This is the rea- 

 son of the greater proportion of azotic gas found in the last 

 cubic inch of the air, which was analyzed on the tenth day. 



If we compare these experiments with the former ones, 

 we must be struck with the great difference between them. 

 The air extracted from water by boiling is much richer in 

 oxygen than common air, containing rather more than 29 

 per cent., while common air contains only 20 per cent, by 

 volume. But this excess of oxygen diminishes rapidly ; so 

 that after four days it does not contain more than common 

 air does. 



Common air, on the contrary, may be left upon the water- 

 trough for ten days without undergoing any sensible 

 alteration in its composition. Indeed, I left nine cubic 

 inches of air in a tube standing inverted over water, from 

 the first of May to the 25th of that month, and found its 

 constituents unaltered. 



If we take the mean of the constituents of air from the 

 preceding table, leaving out the last term, because the sul- 

 phate of iron had increased the quantity of oxygen absorbed, 

 we obtain 



Azotic gas . . 80-32 volumes. 

 Oxygen gas . . 19-68 ,, 



100-00 

 Now this diff'ers very little from the composition of air. 

 If we analyze air without removing previously the carbonic 

 acid gas and the moisture which it contains, we always find 

 the volume of its oxygen below 20 per cent. 



V. — Absorption of Air by Water. 



To determine the absorption of air by water I boiled a 

 quantity of distilled water for a quarter of an hour, and 



