DISSOLVED CONTENT OF WATER. 897 



About 12 parts of sulphuric acid per million kill the same species within 24 

 hours. According to the degree of alkalinity of the water considerable acid 

 may be added before the water becomes acid in reaction. 



This matter of changing the reaction of water is important in connection 

 with some industrial pollutions. An interesting case occurred during the spring 

 of 1905 in the Potomac above Cumberland, Md. A large number of fishes, largely 

 minnows, were found dead and dying along the shore, and still greater numbers 

 were sick and weak and could be picked up in the hand. Twenty-nine miles 

 above Cumberland a paper mill sewers into the river a highly alkaline waste, 

 several tons of lime sludge passing in daily. Shortly below this point Georges 

 Creek enters, carrying an acid waste from the coal-mine regions. It contains 

 free sulphuric acid and salts of acid reaction. The creek water is distinctly 

 sour to the taste and is said to contain no life of any sort. When the two 

 wastes mix at and below the mouth of Georges Creek they neutralize each other, 

 and besides improving the river from a sanitary standpoint permit the fishes of 

 the river to thrive. They must be usually fairly well balanced, since fishes have 

 usually been in some abundance. In October, 1900, on the occasion of a sudden 

 occurrence of dead fishes in the river a sample of water was reported to contain 

 free sulphuric acid, to which the loss of fishes was attributed. On the more 

 recent occasion referred to the water, which was only examined as the fishes 

 were recovering, was not acid, but the alkalinity was reduced, was very low and 

 was rising, and therefore the probability is that the river had just been acid and 

 was recovering its normal alkalinity. It could hardly be expected that the two 

 extensive pollutions mentioned would be invariable in amount, and it can hardly 

 be doubted that the acid occasionally predominates and kills fishes. The acid 

 pollution is by far the more important in its eflfect upon fishes. 



The courts have on occasion held that in the case of coal-mine wastes 

 damages can not be collected nor the mine owners enjoined, since the pollution 

 is a natural one and occurs to some extent independently of mining operations. 

 In the instance cited it would seem that each pollution is the salvation of the 

 river from the other; that the net result is a beneficial one, and that it would be 

 unwise to meddle with either unless it were possible completely to remove both. 



Some natural waters have been observed to acquire a selective toxicity by 

 remaining in tin cans for some time. They become, for instance, fatal to rain- 

 bow but not to brook trout. During the spring of 1907 some results in this 

 respect of much interest were obtained from the city water of Norfolk, Va. 

 Samples transported in new tinned fish cans were uniformly fatal to fry of the 

 rainbow trout, but had little eifect on brook-trout fry. Samples transported 

 in tinned fish cans which had been in use a long time and become rusty on the 

 inside gave contradictory results but were often likewise toxic, though less 



