20 



THE STUDENT'S AQUARIUM. 



managed than when you have a large body of water with a 

 circulation. We must remember, that it will not be the salt 

 which will evaporate but that it will be the water. Where there 

 is a circulation the density of the water must be kept with a 

 lactometer ; but in a small aquarium it can be easily ascer- 

 tained by the sediment on the glass. Particular care must be 

 taken of this sediment ; it must be watched closely, and it will 

 be found that when you fill the tank or globe say within three 

 inches of the top, that after 24 hours it will have a line of sedi- 

 ment on the glass level with the water, this is your lactometer. 

 When the water has fallen one-half inch or more from the line 

 of sediment, that is the amount of water that has evaporated 

 and this must be replaced with fresh water, not salt water, for 

 the salt is still there, it is only the water that has been lost. 

 Again, the aquarium I have recommended for fresh water will 

 not answer for salt water. In the first place, salt water is 

 much more penetrating than fresh, and would work its way 

 through the putty and litharge in a very short time ; and sec- 

 ondly, under no circumstances must you allow salt water to 

 come in contact with metal of any description. If you have a 

 large iron tank, and the glass has been set with some other 

 substance than putty and litharge, or red or white lead, you can 

 make it serviceable by covering the iron with a mixture of % 

 Portland cement and y 3 of sand, — this will be found to resist 

 salt water. But the nicest, cleanest, and in every way best 

 adapted vessel for the Marine Aquarias are those bell glasses 

 with ebonized stands, sold or obtained for you by the glass and 

 china trade throughout the United States. These can be used 

 successfully for all the lower varieties of marine life. You can 

 keep in one, say anemones, barnacles, serpules, coral, clams, 

 and oysters, in another you can keep hermit, spider and rock 

 crabs, star fish, &c, &c. In fact you will find a very large 

 variety of life in the orders mentioned, and with the ways of 

 which you are not acquainted or ever will be until you have an 



