1918 Shelf ord; on Acidity Affecting Fishes 103 



B. Sulphurous acid 



The use of SO, as bubbled through the sewage has been found to 

 be the most economical acid method. It also has a very marked germicidal 

 effect, the number of bacteria being reduced from many thousand to a 

 few hundred per cc. This acid is accordingly most desirable for use in 

 sewage treatment. It is, however, ten times or more as toxic (Shelford, 

 1917) to fishes as sulphuric acid, but has the advantage of escaping from 

 the water very rapidly, and since it is present in the effluent before it 

 is mixed with the sea-water, the bubbling of compressed air through the 

 effluent or a simple stirring or other exposure would very quickly remove 

 any dangerous effect which it might have on organisms. It differs in this 

 respect from H2SO4, which liberates poisonous carbon dioxide by a 

 chemical reaction which takes place only after the effluent and the sea- 

 water are mixed. Thus on account of the ease with which it may be 

 removed and its germicidal effect it is much more desirable for use than 

 H2SO4, Turning to table 3 we note that from 2.3 to 2.9 parts per million 

 are required to kill a 2.25 gram herring in an hour, and that 4 parts per 

 million are very quickly fatal. It was found with the gradient tank that 

 herring recognize a difference of one part per million in the concentration 

 range from parts per million at one end to 3 parts per million at the 

 other (chart 1, graph 3). They turn back from slightly higher concen- 

 trations but are positive to very strong solutions (chart 1, graphs 4 and 5). 

 In the case of the perch, 3.9 to 4.3 parts per million killed the fish in 3^ 

 hours while 9 parts per million were very rapidly "fatal. Only one flat 

 fish was killed in the sulphurous acid water, and this after 40 minutes 

 exposure to water containing about 9 parts per million. In sulphurous 

 acid the perch is only a little over twice as resistant as the herring, and 

 the flat fish about five times as resistant as the perch. The question of 

 treatment of the effluent by allowing it to flow over limestone received a 

 little attention. It was found, however, that in running water calcium 

 hydrogen sulphite is less toxic to herring than sulphurous acid, but in 

 standing water the salt is more toxic than the acid on account of the rapid 

 escape of the SO,. Thus in standing water requiring .6 cc. of N/100 

 iodine per 100 cc. in the cases of the three compounds — sulphurous acid, 

 calcium hydrogen sulphite and calcium sulphite - — death resulted in 85 

 minutes in the acid, and in about 50 minutes in each of the other two. 

 There would seem to be no advantage from the standpoint of fishes, in the 

 treatment of the effluent with limestone. 



C. Acids from munition xvorks and their effect upon fishes 

 We have already noted that the killi-fishes were repelled from the 

 New Jersey tide waters by the acids from muition works (Shelford, 1918b). 



