io THE POPULAR SCIENCE MONTHLY. 



Indeed, that water, especially when not in motion, will absorb 

 gases, including putrefactive and septic germs, is a well-established 

 fact ; and it is equally well established that germs will live and multi- 

 ply in water, and that they will even, in some cases, survive the action 

 of frost upon the water. Germs in a condition of extreme desiccation 

 and apparently long dead will, on being treated with moisture, if other 

 circumstances are favorable, become revivified and developed into their 

 most perfect and active forms. 



It being indisputable that germs may be absorbed by water, and 

 that they may multiply in water, it seems irrational that they should 

 not by evaporation, or by the means of minute bubbles generated by 

 decomposition of organic matter in the w r ater, or by agitation of the 

 water, escape into the surrounding atmosphere. 



Professor Kerr, in an address before the British Civil and Mechan- 

 ical Engineers' Society, said : 



We know that gas is generated by the decomposition of the decaying matter 

 in sewage when deposited, in however slight a degree, upon any interior surface. 

 What followed? We know this gas has two qualities which are extremely 

 obnoxious : one quality was that it ascended to the highest level by reason of 

 deficient specific gravity ; and the second quality was that when it reached the 

 highest level it exercised a pressure, being an extremely elastic gas. He need 

 scarcely point out the effect of these two considerations. When the sewer-gas 

 (a most excellent name, without going into particulars as to whether it should 

 be called gas or vapor; the name sewer-gas carried an idea of offensiveness 

 which was extremely convenient) when the sewer-gas had reached the highest 

 level, it exercised a powerful elastic pressure to force its way out, and succeeded 

 in forcing its way. It got into the houses ; and if there were no other grievance, 

 there was this to complain of that this pestiferous and poisonous gas forced its 

 way from the sewers into our houses, and, of course, reached the vital organs of 

 those who occupied them. 



Must we, then, accept as final the experiments made by Dr. Carmi- 

 chael, and perhaps a few other experimenters ? May we safely con- 

 clude that the gases and germs contained in the sewers can be effectu- 

 ally excluded by water-traps ? That well-sealed water-traps afford 

 some protection can not be questioned ; but the experiments of Car- 

 michael seem to me far from having rendered it certain, or even prob- 

 able, that they insure absolute safety. 



The reader will observe, however, that, even if we admit that the 

 experiments of Carmichael establish all that has been claimed for them, 

 it is still none the less a fact that the water-traps give us no protection 

 when they are empty or defective ; and examples abound in the expe- 

 rience of almost every plumber, in which the traps are found empty, 

 either in consequence of the direct pressure of the air from below, or 

 of siphonage, or of leakage ; the leakage being sometimes due to the 

 erosive action of the gases, to which action the traps are especially 

 exposed, and sometimes to cracks occasioned by contraction and ex- 

 pansion, resulting from the alternate admission of hot and cold water, 



