1816.] the Absorption of Gases ly Water. 219 
obtained from water by heat, by the air-pump, &c. to corroborate 
the absorption, The best and readiest method of all is to expel 
the atmospheric air by hydrogen, in which case the air expelled 
and the hydrogen absorbed are immediately determined by well 
known methods ; but to those who do not understand the theory of 
this proeess it can be of little use. The quantity of oxygen in 
water is accurately ascertained by agitating with nitrous gas, as [ 
stated in the paper 12 years ago, allowing 3°4 nitrous for 1 oxygen, 
or perhaps more correctly 3°6 for 1. The point of saturation is 
when neither of the gases is found in the residue. Another very 
easy method of determining the oxygen in water has recently 
occurred to me, and in about a dozen trials I have found it never 
deviate, though made upon very different quantities of water, 
namely from five ounces to 200; it has one advantage too, that it 
requires no great skill either to execute or comprehend it. I 
will relate one of the experiments. 
18 ounces of clear rain-water and three of lime-water were 
briskly agitated together in a tall cylindric jar, so as to acquire a 
full charge of atmospheric air; after standing a few minutes 
13 grain measures of a solution of green sulphate of iron (1°157 = 
32 salt = 1 oxide) were put into the water and gently agitated 
with a rod for five minutes. In half an. hour a pure yellow oxide 
had subsided. The water was drawn off by a syphon, and seven 
grains more of the sulphate were put in and agitated as before; in 
a quarter of an hour a perfectly green oxide had subsided, which 
preserved its colour for many days under the water. Now if Saus- 
sure’s estimate of oxygen in water be admitted, the last should 
have been a perfect yellow oxide. . Allowing 4 of the weight of 
the green oxide for the additional oxygen, we find about 80 grain 
measures of oxygen gas in 21 oz. of water, or 10080 grains. If 
the water had been charged with pure oxygen the quantity would 
have been 400 grains, or nearly four per cent., instead of 6*5, and. 
five times the quantity of sulphate would have been required, as I 
have repeatedly found, No oxygen is found in water after the 
green oxide begins to be permanent. 
Though the quantity of oxygen gas absorbed by water appears to 
me decisively to be 3°7 per cent. as I before determined, or perhaps 
4 +, when recent agitation in the purest gas has been used, yet I 
do not find the same degree of accuracy in my former results in 
regard to azote; I have repeated some of my experiments and find 
that water takes 21 per cent. of azote as nearly as possible, and. not 
1:56 as I formerly stated, nor yet 4:1 as Saussure states. Both 
Henry and Saussure are wrong I believe in placing azote below 
hydrogen ; this last is the least absorbable ; water takes very nearly 
two per cent. of hydrogen. Henry says, 1°6, and Saussure, 4:6; 
but it must be understood that both of these chemists profess to 
give the observed absorption by water purified -ly boiling only, and 
not absolutely pure; whereas the numbers I have given above are 
understood of absolutely pure water. If we allow that 4 part of 
Pp 2 
