5700 The Aquarium. 



power of absorbing gaseous bodies in varying proportions, thus : — 

 J 00 volumes of water, at a temperature of 60° Fahr., and under ordi- 

 nary barometric pressure, will absorb 



1*56 volumes of nitrogen gas, 

 3-70 „ oxygen gas, 



10000 „ 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 38 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 life; 

 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 7\ oz. 



„ lime 2| „ 



Chloride of sodium 43| „ 



„ magnesium 6 „ 



„ potassium \\ „ 



Bromide of magnesium , 21 grains 



Carbonate of lime 21 „ 



These quantities will make ten gallons. The specific gravity of sea 

 water averages about T025 ; and when from evaporation it reaches 

 above this, a little rain or distilled should be added, to restore it to 

 the original density. 



* This is prepared by Messrs. Brew and Schweitzer, of 7J, E.ist Street, Brighton. 



