THE YOUNG SCIENTIST. 
21 
Eecipes for ebonizing are quite numer- 
ous, and one or two good ones can be 
found in back numbers of the Young 
Scientist, which, if closely followed, will 
give good satisfaction. 
In conclusion, let me say that I will be 
hai^py to aid any of my young readers 
who may wish to make one of these 
cabinets, if they will acquaint me of their 
wants either through these pages or in 
care of the editor. 
The Aquarium.— New Mode of Aerating 
the Water. 
SO important do we regard the subject 
of the aeration of water that we shall 
endeavor to present it to our readers in 
another way. Let us suppose a tank 
holding 124 gallons of water or 100 pints. 
This amount of water would at the freez- 
ing point hold in solution— 
Of nitrogen, . . . 2 pints 
oxygen, . . . 4 " 
" carbonic acid, . . 179 " 
But when the temperature of the water 
rises to 60° Fahr., these quantities are re- 
duced to the following : 
Nitrogen, . . . 1.4 pints 
Oxygen, ... 3 
Carbonic acid, . 100 " 
The pressure is assumed to be the ordin- 
ary pressure of the atmosphere. The 
quantity of gas absorbed increases with 
the pressure, as we see in the case of 
ordinary soda water, when a large quantity 
of carbonic acid is forced into the water by 
pressure, and remains quietly dissolved 
until this pressure is removed, when it at 
once escapes, causing a strong efferves- 
cence. The common " siphon " bottles 
show this very well. 
The fact that as the temperature rises 
the gas which is dissolved in the water 
tends to escape, is well illustrated by a 
tumbler of common well water freshly 
drawn. Such water is generally cold ; if 
brought into a warm room it at once gives 
off a large amount of gas, which appears 
as bubbles adhering to the sides of the 
tumbler. 
So much for the capability of water to 
absorb gas. We now pass to a consider- 
ation of the conditions under which gas 
will be absorbed. It is evident that if no 
change is going on in the water, that is to 
say, if no plants or animals are present to 
absorb one kind of gas and give off 
another, any body of water will soon be- 
come saturated with air and will remain 
so. But if animals are present to use up 
the oxygen, and there are no plants to 
furnish a fresh supply, it will be found 
that the rapidity with which the water 
absorbs oxygen is exactly proportioned 
to the extent of surface exposed. Hence 
the practical conclusion that we must 
spread out the water of an aquarium if 
we would have it thoroughly aerated with- 
out the aid of plant life. And as in most 
aquaria the animals are kept in excess, it 
happens that those who have tanks which 
expose a large surface to the air, in pro- 
portion to the quantity of water presentj 
generally have the best success. There 
are other conditions, however, which enter 
into this question, and which confer cer- 
tain advantages on deep aquaria, and 
these we will consider hereafter. Mean- 
while let it be understood that where 
water is aerated either by mere exposure 
or by mechanical means, everything de- 
pends upon the extent of surface which is 
exposed. Therefore, if you have gold fish 
in a glass globe, do not fill it too full. As 
soon as the water rises above the middle 
of the globe, the water surface diminishes, 
and the fish feel the want of air. No 
vessel of a globular shape should ever be 
filled more than two-thirds full. 
When air is pumped into water, as was 
done in Barnum's old museum and in the 
tanks of the New York Aquarium, now 
also defunct, it will not do to pass the air 
into the water from the end of an open 
pipe, as is generally done. In this case 
the air passes through the water in large 
bubbles which expose very little surface 
in proportion to the amount of air that 
they contain, and consequently very little 
air is absorbed. Moreover, a large bubble 
ascends through the water more rapidly 
than a small one, and consequently time 
enough for absorption is not allowed. 
Some have sought to remedy this by a 
piece of wire gauze over the end of the 
pipe, but this does not answer, as, after 
passing through the gauze, the several 
