466 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



As sea-water aquaria have a great future iu Germany and will rap- 

 idly increase in number if proper directions for their maintenance are 

 given, I will describe the mauufucture of the water in such a manner 

 that any onecan easily prepare it himself. To 50 liters (about 13J gallons) 

 of pure hard well water take 1,325 grams (46i ounces) of common salt, 

 100 grams (about 3J ounces) of sulphate of magnesium, 150 grams (about 

 5J ounces) of chloride of magnesium (chlormagnesium), and 60 grams 

 (about 2 ounces) of sulphate of potassium, all of which can be obtained 

 at any drug store, but generally not entirely pure; and foreign admix- 

 tures and impurities may easily cause the death of all the animals. Each 

 of these chemicals is dissolved in water by itself; afterward they may 

 all be poured together and allowed to stand quietly for several hours, 

 so that little stones and other impurities may settle to the bottom. All 

 particles of dirt floating on the surface should be carefully removed by 

 dipping. The mixture is then poured into another vessel and diluted 

 with fresh water until the hydrometer indicates the proper degree of 

 saltness. The quantities given above will produce about 50 liters (about 

 13^ gallons) of sea-water. 



This composition I have ascertained comes very near to that of 

 natural sea-water, for, besides the component parts given above, it also 

 contains small quantities of soda, iron, and potash. I obtain the chem- 

 icals for preparing my sea-water, which contains all the seven ingredi- 

 ents in their true proportions, from a friend of mine who is a chemist 

 and am prepared to supply others. Most of the sea-water found in the 

 market contains only the four first-mentioned salts, and is likewise suit- 

 able for filling the basin. One should be careful, however, not to put ani- 

 mals in such freshly manufactured sea- water, as this would almost beyond 

 a doubt kill them. It is well known that sea- water is 0.027 gram heavier 

 than fresh water; its weight is therefore 1.027. Everything in excess 

 of this weight must be carefully corrected from time to time by pouring 

 in fresh water as the water evaporates, while this is not the case with 

 the salts. The solid ingredients of sea-water constitute about 3^ per 

 cent, of its weight, or one-half ounce to a pound of water. A hydrom- 

 eter is indispensHble for ascertaining the degree of saltness. 



Newly manufactured sea-water should be placed in the open air in 

 some cool place, and allowed to staiid for some time. If one has any 

 live salt-water algte adhering to stones they should be added, because 

 they impregnate the water with oxygen. After some weeks the algae 

 will spread all round them clouds of diminutive seeds, which adhere to 

 the walls and quickly grow under the influence of light. By supplying 

 oxygen they make the water, after it has been filtered several times, 

 still more fitted to receive animals. Of sea-plants, the green ulvse and 

 the confervfe are particularly suitable for recently manufactured salt 

 water. 



In the beginning only a few hardy animals should be placed in the 

 water, which will flourish and thrive in it; and after awhile an at- 



