304 



L. H. HYMAN. 



than that produced by HC1. Some detailed data on sulphuric 

 acid are given in Table IV. and the results of all experiments 

 with nitric and sulphuric acids are summarized in the general 

 table, Table VI. 



TABLE VI. 



SUMMARY OF ALL EXPERIMENTS WITH ALL ACIDS, GIVING THE AVERAGE 



PERCENTAGE OF DEPRESSION ON INITIAL EXPOSURE 



TO EACH ACID AT EACH pH USED. 



.6. Experiments with Carbonic Acid. Carbon dioxide gas was 

 passed through the water until the desired acidity was obtained. 

 In this procedure great care was necessary to avoid depriving 

 the water of its oxygen, since when a gas bubbles through a liquid 

 it removes other gases. The water had to be vigorously shaken 

 with air after the carbon dioxide had been added. A good deal 

 of manipulation is required when working with higher concen- 

 trations of carbon dioxide to secure the proper amount of oxygen 

 and carbon dioxide simultaneously in the water. In all of the 

 experiments reported the oxygen content of the water was ample. 

 It may be noted in passing that a combination of low oxygen 

 with high carbon dioxide has a much greater depressing effect 

 than either of these conditions separately. Under ordinary con- 

 ditions the rate of oxygen consumption is normal in water 

 containing 2 cc. per liter but oxygen consumption is almost 

 abolished in such water if it be saturated with carbon dioxide. 

 When plenty of oxygen is present, the depression produced by 

 saturated carbon dioxide is only about 50 per cent. 



Most of the experiments with carbon dioxide are reported in 

 Table V. In the more dilute solutions pH 7.5 to 7.0 carbon 

 dioxide acidity produces less depression than do other mineral 



1 Animals injured. 



