70° PROCEEDINGS OF SOCIETIES. 
temperature of 60° Fahr., and under ordinary barometric 
pressure, will absorb— 
1:56 volumes of nitrogen gas, 
3°70 AS oxygen gas, 
100:00 if carbonic acid gas ; 
and hence we find that the air absorbed by water, and existent 
in rivers to the extent of from 2 to 3 per cent., consists of 
about 29 of oxygen and 71 of nitrogen. In fresh-fallen rain 
and melted snow it ranges from 30 to 35 per cent. of oxygen, 
and in some spring waters it has reached as high as 88 per 
cent. This oxygen, by the process of respiration, is converted 
into carbonic acid gas, or mephitic air, the choke damp of the 
coal-pit, a gas highly poisonous to animal hfe; but here 
comes into play that beautiful and wonderful provision which, 
by the action of growing vegetation under the influence of 
the sun’s light, converts this baneful agent into vital oxygen, 
the ‘ breath of life.” 
Water, fresh and marine.—The water used for the aquarium 
should be clean, and taken direct from a river, or from a soft 
spring, and should not have been purified by means of lime. 
As regards sea water, it should, if possible, be taken at a 
distance from shore, and at the period of high water. If 
artificial sea water is employed, it should be made either 
from the saline matter obtained by the evaporation of sea 
water,* or by the following formula: 
Sulphate of Magnesia . . 71 07. 
ES inane)? ay See 
Chloride of Sodium . . . 484 ,, 
7 Magnesium. . 6 ,, 
2 Potassium’ a 
Bromide of Magnesium. . 21 grains. 
Carbonate of Lime . . . 21 
+) 
These quantities will make ten gallons. The specific gravity 
of sea water averages about 1-025 ; and when from evaporation 
it reaches above this, a little rain or distilled should be added, 
to restore it to the original density. 
Vegetation —The plants best fitted for fresh water are the 
Valisneria spiralis, the Myriophyllum, Ceratophyllum, and 
the Anacharis, all of them submersed plants, and fulfilling 
the purposes required most admirably. From the great sup- 
ply of food in the aquarium, the growth of the Valisneria is 
very rapid, and it requires, therefore, to be thinned by weed- 
* This is prepared by Messrs. Brew and Schweitzer, of 71, East Street, 
Brighton. 
