OXYGEN CONSUMPTION IN ACIDS. 293 



this acidified water for one or more successive periods of time 

 determined. The animals were placed in Erlenmeyer flasks, if 

 small, or in wide-mouthed salt bottles, if large, of about 500 cc. 

 capacity. The water to be used was thoroughly aerated and 

 placed in a large elevated receptacle. From this it was siphoned 

 into the flasks or bottles containing the animals and allowed to 

 flow out at the top for a few minutes. The flasks or bottles 

 were then tightly closed and kept in a water bath at constant 

 temperature for the desired length of time, generally one hour. 

 After thoroughly shaking the contents, a sample of 125-150 cc. 

 was then drawn by siphon and analyzed for oxygen content by 

 Winkler's method. Blanks of the water used were of course also 

 drawn at the beginning of the experiment and allowed to stand 

 in the water bath with the animals until the end of the test. 

 The difference between the oxygen content of these blanks and 

 the samples drawn from the flasks or bottles containing the 

 animals gives, after suitable calculation, the amount of oxygen 

 consumed by the animals in the time selected. Immediately 

 after drawing the normal samples, the acidified water was added 

 in the same way and the animals allowed to respire in the acidified 

 water for the same length of time. This was repeated as many 

 times as desired, using the same animals and the same degree of 

 acidification in any one series of experiments. The water was 

 freshly acidified and aerated for each of these determinations. 

 There is no possibility that alterations in the oxygen content of 

 the water in any way affected the result, as the oxygen content 

 was at saturation at the beginning of each test, and the test 

 continued only long enough for the animals to use up a small 

 part of the oxygen present. 



The hydrogen ion concentration was determined by means of 

 indicators purchased from the La Motte Chemical Products 

 Company. A set of standard tubes covering the range from pH 

 3.0 to pH 8.4, with indicators brom phenol blue, brom cresol 

 green, brom cresol purple, and phenol red, was employed. 

 Solutions of these indicators were obtained from the same com- 

 pany. A few drops of the appropriate indicator added to 10 cc. 

 of the water to be tested yields a color which can be compared 

 with that of the standard tubes; the approximate pH is thus 



