Preparation of Sea Water for the Aquarium. 131 



small, compared in weight or bulk, with that of the stones it 

 binds together. 



Seeing, however, that the internal and external skeletons, 

 habitations, or other solid appendages of many of the animals 

 kept alive in aquaria, consist of carbonate of lime, along with 

 some phosphate of lime, and a little fluoride of calcium, 

 whilst others consist of silica — those substances besides iron 

 must be contained in the water in which these creatures dwell. 



Again, to refer to sea plants, Mr Gosse excludes from his 

 sea water, soluble bromides, and, as appears, also iodides, be- 

 cause thej occur in the ocean in small quantities. Yet it is 

 quite certain that many sea-weeds concentrate within them- 

 selves much iodine as well as a little bromine, and both, but 

 especially the former, must be held to be serviceable to those 

 plants. It may be added, that although no minute inquiry 

 into the matter has been made, both iodine and bromine oc- 

 cur in the organs of sea animals, for example, in the liver of 

 the cod ; and it is impossible to believe that such powerful re- 

 medial agents, can be without an influence on the health of the 

 animals receiving them. Iodides and bromides, therefore? 

 should be present in the imitation sea-water. 



Nor would there be any difficulty in supplying the desi- 

 derata indicated. As calcareous phosphates, carbonates, and 

 fluorides occur together in shells, corals, and many limestones, 

 and in the proportion in which sea animals require them, the 

 arrangement of fragments of such calcareous bodies at the 

 bottom of the aquarium would suffice ; — for the carbonic acid 

 produced by the animals within it would slowly dissolve the 

 lime-salts as they were needed. 



Pieces of felspar or of any of the trap rocks containing al- 

 kaline silicates would in the same circumstances furnish 

 silica. It would not probably be requisite to make a deli- 

 berate addition of sulphate of lime, as the sulphate of mag- 

 nesia and the calcareous fragments would supply its elements. 

 If it were thought necessary to add it, a solution, containing 

 about a grain of sulphate of lime to the ounce of water, can 

 be easily prepared by shaking the latter with some burned 

 stucco powder, and of this a measured quantity could be 



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