THE MARINE AQUARIUM 59 



The composition of sea water is as follows : 



Water 96'47 per cent. 



Sodium chloride . . . 2-70 



Magnesium chloride ... '36 



Magnesium sulphate (Epsom salts) . "23 

 Calcium sulphate .... -14 



Potassium chloride . . . . "07 

 Traces of other substances '03 



100-00 



and it will be seen from this table that artificial sea water may be 

 made by adding about three and a half pounds of sea salt, obtained 

 from the sea by the simple process of evaporation, to every ninety- 

 six and a half pounds of fresh water used. In making it there may 

 be some difficulty in determining the weight of the large volume of 

 water required to fill an aquarium of moderate dimensions, but 

 this will probably disappear if it be remembered that one gallon of 

 water weighs just ten pounds, and, therefore, one pint weighs 

 twenty ounces. 



If the sea salt cannot be readily obtained, the following 

 mixture may be made, the different salts being purchased 

 separately : 



Water 96 Ibs. 



Sodium chloride (common salt) . . 43 ozs. 



Magnesium chloride 5 J 



Epsom salts 3f ,, 



Powdered gypsum (calcium sulphate) . 2 



Although in this mixture the substances contained in the sea in 

 very small quantities have been entirely omitted, yet it will answer 

 its purpose apparently as well as the artificial sea water prepared 

 from the true sea salt, and may therefore be used whenever neither 

 sea salt nor the natural sea water is procurable. 



Assuming, now, that the aquarium has been filled with sea water, 

 it remains to introduce the animal and vegetable life for which 

 it is intended ; and here it will be necessary to say something 

 with regard to the amount of life that may be safely installed, and 

 the main conditions that determine the proportion in which the 

 animal and vegetable life should be present in order to insure the 

 greatest success. 



