1877.] 



Organic Matter in Potable Water. 



155 



was the preserving agent, a stoneware vessel was charged underneath the 

 spongy iron with pyrolusite and sand, so as to abstract the iron from the 

 water before it came in contact with the meat. After four weeks' filtra- 

 tion the latter was found perfectly fresh. 



Experiment VII. — By a separate experiment I ascertained that the 

 oxygen is completely abstracted from water during its passage through 

 spongy iron. In order to determine whether the absence of oxygen be 

 the cause of the preservation of the meat, and whether the Bacteria or 

 their germs be killed or can be revived when supplied with oxygen, an 

 evaporating-basin was inverted over the meat. This must have retained 

 a quantity of air in its cavity, the air being gradually dissolved by the 

 water in close proximity to the meat. After four weeks' filtration the 

 meat was perfectly fresh ; I succeeded in collecting a small bubble of the 

 gas, still in the cavity of the evaporating-basin. This was quite free 

 from oxygen. 



It is therefore doubtful whether oxygen was supplied to the water 

 sufficiently long to justify any conclusions from this experiment. How- 

 ever, the result of experiment Till, rendered a repetition unnecessary. 



Experiment VIII. — Fresh meat was placed at the bottom of a glass 

 vessel and left standing, covered with about four inches of spongy iron 

 and water. The vessel in this instance was not boiled. After three 

 weeks the meat was very bad, demonstrating that the action of the 

 Bacteria of putrefaction adhering to the meat was not prevented by 

 the spongy iron above; and if, during the previous experiments with 

 spongy iron, agencies capable of causing putrefaction had at any time 

 come in contact with the meat (in other words, if the Bacteria had 

 not been killed in their passage through spongy iron), the meat must, 

 as in this last experiment, have shown marks of their action. It 

 therefore appears that Bacteria are permanently rendered harmless 

 when passing in water through spongy iron. This conclusion is further 

 corroborated by the observation that even effluent sewage-water, after 

 passing through the spongy material, has remained perfectly bright for 

 now five years when exposed to light in a half-filled stoppered bottle. 



I believe that the action of spongy iron on organic matter largely 

 consists in a reduction of ferric hydrate by organic impurities in water. 

 "We know that even such organic matter as straw or branches is 

 capable of reducing ferric to ferrous hydrate. We know that even 

 such indestructible organic matter as linen and cotton fibres is 

 gradually destroyed by rust-stains. This action is slow when experi- 

 menting upon ordinary ferric hydrate ; but it may, in statu nascendi, be 

 very energetic — the more so, if we consider the_ nature of the organic 

 matter in water. Eerric hydrate is always formed in the upper part of 

 a layer of spongy iron when water is passed through that material. The 

 ferrous hydrate resulting from the reduction by organic matter may be 

 re-oxidized by oxygen dissolved in the water, and thus the two reactions 



