920 Vindication of Dalton’s Theory of ([Marce, 
the air still remains in water after long boiling (which is no uneom- 
mon circumstance); then Henry’s numbers would be 1-9 for 
hydrogen, and Saussure’s 5°5, making an enormous disproportion 
in their errors. 
When water is violently agitated with any kind of gas, it is some 
time before the surplus gas mechanically diffused through the water 
in small bubbles makes its escape: after all there is probably a sur- 
charge; the quantity of the surcharge Ihave endeavoured to inves- 
tigate; it is an object of some consequence in a theoretic point of 
view. The following may be of some use to such as choose to take 
up this subject. When a gallon of water (or about + of a-cubic 
foot) is well boiled, and then poured into a cylindric jar, so as to be 
about eight inches deep, and suffered to remain exposed to the 
atmosphere without agitation, it recovers one half of its air in two 
days. In 10days no further absorption is remarked; but by violent 
agitation it will take ~5 or 1, of a full charge. It should be 
known that water requires about one minute’s agitation to acquire a 
full charge of any gas, when previously as free as possible from air, 
supposing the water to be about 20 times the volume of air; but 
if the water be 30 or 40 times the air, it may require two or three 
minutes’ agitation. I seldom allow less than five minutes. 
It is not very obvious to me why Saussure has passed ovet an 
important feature of the theory of absorption without any notice I 
can find. I mean the effect of heat. He has some allusions to it 
in the paragraph announcing his modes of freeing liquids from ‘air ; 
but they are evidently accidental, and he enters upon no explana- 
tion. He suggests two methods of expelling air (or rather suffer- 
ing it to escape) from liquids; the one is, by removing the incum- 
bent air from their surfaces and substituting steam of equal pressure 
(that is, boiling the liquids); the other is, by removing the incum- 
bent air and substituting steam of very weak pressure, (that is, by 
the air-pump.) He observes that in the last case “ the pressure of 
the vapour prevents the escape of the air.” Jt would be very 
reasonable to ask why the pressure in the former case does not'muach 
more prevent the escape of the air. The only answer, 1 con- 
jecture, that Saussure and you could give, would be that the heat 
of boiling water expels the air with so much force, that a counter- 
acting pressure equal to that of the atmosphere is insignificant. 
The truth is that neither the heat nor the vapour has directly any 
influence upon the expulsion or retention of the air. If a tube 
half filled with water and half with air be hermetically ‘sealed, it 
may be put into freezing water, or boiling water, ‘which ever we 
please, for half an hour, and no air will be observed to pass either 
into or out of the water, though the pressure of the incumbent 
steam varies from 1 to 150, and the temperature from 32° to 212°, 
The same tube open at the end immersed in boiling water would in 
half a minute be quite opake with ascending air bubbles. 
‘M. Saussure and you have represented it as my theory, that 
** all liquids” absorb the same quantity of air as water does, (p. 339, 
2 
