358 
DU. DALTON ON THE CONSTITUTION OF THE ATMOSPHERE. 
sures from the middle or near the bottom of the jar, and charged it with air to the 
full by agitation. The bottle of water imbibed 
The water taken near the surface. 
These portions taken up consisted nearly 
one half of oxygen. 
es. 
From these experiments it would appear that by boiling water briskly for three or 
four minutes, about half of the atmospheric air previously in the water escapes along 
with the steam. But it requires much longer boiling and keeping the atmospheric 
air as much as possible from the surface of the water to get the rest of the air ex- 
pelled. It is never all expelled by boiling, except in the construction of a good water 
hammer. Any one air not chemically combined with water is easily and effectually 
expelled from it by repeatedly agitating the water with another kind of air. 
It also appears that water deprived of its atmospheric air, if kept at rest, acquires 
the air again slowly, and more so if the surface exposed is small. But if violent agi- 
tation of the water, so as to mix the atmospheric air and it intimately together, be 
used, the full impregnation is effected in one or two minutes, as I have elsewhere 
shown. 
Trough waters being mentioned above (3.) it may be well to explain some of the 
circumstances affecting it. The waters I use for the chemical trough is rain-water ; 
it is preferable to pump water by its freedom from carbonic acid and earthy salts ; it 
is slightly coloured at first when drawn from the cistern, but it soon becomes clarified 
by standing: my trough contains about nine gallons when in work. I take great 
care to put nothing in it which can materially affect its purity ; small portions of 
lime water and of some iron and other salts are the chief impurities which are ad- 
mitted ; no sulphurets or hydrosulphurets are allowed to enter, and very little of 
either acids or alkalies. I examine the state of the water occasionally ; lately, after 
it had been more than half a year in the trough, though not very frequently used, I 
had the curiosity to examine its state before the trough was emptied. The water was 
neutral by the colour test ; it contained about 50 grains of saline matter in the gal- 
lon ; it was transparent, but slightly milky ; prussiate of potash gave sensible blue ; 
oxalate of ammonia, muriate of barytes, and carbonate of soda produced a white pre- 
cipitate. The taste was like that of earthy pump water. It had its full share of 
The first day . . . 
16 measures. 
The second day . 
15 measures. 
The third day . . 
12 measures. 
The fourth day . . 
10 measures. 
The fifth day . . . 
10 measures. 
The sixth day . . 
9 measures. 
The seventh day. . 
4 measures. 
The eighth day . . 
7 measures.^ 
The ninth day . . 
9 measures. 
The tenth day . . 
7 measures.^ 
The fifteenth day . 
2 or 3 measu 
