DISSOLVED CONTENT OF WATER. 905 



exposure to air is concerned, but they readily clog with suspended matter. 

 Moreover, they do not allow the delivery of so much water as larger holes, unless 

 the pressure is increased by deepening the pan, but this takes up vertical space. 

 Larger holes to avoid clogging may be compensated by more pans. The size 

 and depth of pans, number and size of holes, will be a resultant of the various 

 factors mentioned, and may be determined by the judgment of the fish culturist 

 for each particular case, or by trial and experiment. 



Since the water from the well under consideration has a temperature of 

 15.5° C. or 60° F., when it arises, it can not undergo warming and remain fit 

 for trout. Could it be passed through an efficient aerating apparatus of pans, 

 trout could probably be maintained in it even during the heated season, since 

 the passage through pans is rapid enough to warm the water but little. Any 

 form of aeration, however, will seriously interfere with the clearness of this 

 water, since it contains about four parts of iron per million dissolved as some one 

 of the salts of iron. On exposure to air most of this iron is precipitated, and 

 causes a marked turbidity. On standing, the particles of iron oxide settle and 

 the water becomes clear; but for constant-flow aquariums it would require 

 filtering before use. This would warm the water, and its use therefore would 

 involve more trouble and expense than that which the well water was intended 

 to obviate. 



Thus this well water is of peculiar interest in having two faults, the cor- 

 rection of which induces a third almost as serious for exhibition aquarium 

 purposes. The excess of nitrogen or the deficiency of oxygen are either of them 

 singly sufficient to kill all the fishes placed in the water. Both are remedied 

 simultaneously by one process, thorough exposure of the water to air; but this 

 process creates, by oxidation and precipitation of dissolved iron, a turbidity 

 which ruins the water for the purposes of aquarium exhibit. 



DETERMINATION OF SUITABILITY OF WATER FOR FISH CULTURE. 



Entirely aside from any question of parasitism, and speaking only of dis- 

 solved substances, it must be admitted that there is at present no sure method 

 of determining by chemical tests the suitability of water for fish culture. Much 

 of course may be assumed in favor of unpolluted natural streams, as trout 

 streams for trout culture. With spring water nothing may be assumed. Some- 

 thing may be learned from a chemical examination, but it must be adapted to 

 the purposes of fish culture. Ordinarily, if a sample is submitted to a chemist 

 he will make what is called a sanitary analysis, which determines whether water 

 is fit for drinking and domestic uses — is healthful for human consumption. 

 For fish culture this is almost useless. Water with a good sanitary showing 

 may kill fishes in a short time, and on the other hand, in rivers fishes are not 



B. B. F. 1908— Pt 2—15 



