32 Ciucinnati Society of Natural History. 



the internal being 34° higher, all openings in the wall being 

 sealed, 1,066 cubic feet of air passed per hour through the walls 

 and floor into the room and up the chimney. Again, with a 

 difference of only a few degrees between the internal and 

 external temperature, it was found that the air passing 

 through a superficial yard of wall line per hour varied 4.7 

 cubic feet for sandstone, 7 and 7.9 for brick, 10 for tufaceous 

 limestone to 14.4 for nuid. The bearings of these facts upon 

 cellar and first-floor rooms for habitation are evident. 



Ice, formerly supposed to be a purifier, is now known to be 

 quite infectious at times — contains microbes in considerable 

 numbers — and has produced local outbreaks, notabl)- in the 

 case of a hotel at Rye Beach, N. H., where the ice was 

 obtained from a pond to which much sawdust and debris had 

 drifted. 



PURIFICATION OF W.VTKKS. 



Recent investigations show that the self-i)urification of 

 rivers is due to three main factors : 



1. The rush of pure water and the consequent dilution of 

 the inquire substances. 



2. The chemical processes which take place under the 

 influence of the atmospheric oxygen and of micro-organisms, 

 and perhaps also the intervention of a(|uatic plants. 



3. The deposition of the heavy substances, and the nmd on 

 the bed and sides of the river. 



" All of these researches ha\e more or less completely 

 demonstrated that the organic substances, the ammonia, the 

 bacteria, introduced into the waters of the rivers that have 

 been studied, diminish at a conqiaratively short distance from 

 the point of pollution, while at the same time those products 

 increase which indicate that oxidation lias taken ]:>lace, such 

 as nitrous and nitric acids." 



(The Sanitary Record, Februar\ i. 1S92, ]). 381.) 

 The former belief in regard to ]nirification of running 

 water in rivers, etc., was that within short distances the 

 oxidation of the inq)urities and their neutrali/.ation was 

 secured by motion and the presence of the oxygen in the 

 water. vSince the introduction of bacteriological methods, 

 tliat is not relied ujion. Though chcuiical examination iiia\- 



