348 Proceedings of the British Association for 1850. 



in it. If the soil, says Dr Smith, has such a power to decom- 

 pose by oxidation, we want to know how it gets so much ot 

 its oxygen. We must, however, look to the air as the only 

 source, and see how it can come from it. When water be- 

 comes deprived of oxygen, it very soon takes it up again, — 

 as may be proved by experiment. This shows us, that as fast 

 as the oxygen is consumed by the organic matter it receives 

 a fresh portion, conveyed to it by the porous soil. Several 

 experiments of the following character were given, to show 

 the filtering power of the soil. A solution of peaty matter 

 was made in ammonia ; the solution was very dark, so that 

 some colour was perceived through a film of only the twentieth 

 of an inch in thickness. This was filtered through sand, and 

 came out perfectly clear and colourless. Organic matter dis- 

 solved in oil of vitriol was separated from it by a thickness of 

 stratum of only four inches. A bottle of porter was by the 

 same process deprived of nearly all its colour. The material 

 of which this filter is made is of little importance. One of 

 the best, according to Dr Smith, as far as clearing the water 

 is concerned, being of steel filings, — oxide of iron, oxide of 

 manganese, and powdered bricks all answering equally well. 

 This shows that the separation of the organic matter is due 

 to some peculiar attraction of the surfaces of the porous mass 

 presented to the fluid. — This paper was a continuation of Dr 

 Smith's Report, published last year ; and he purposes con- 

 tinuing the inquiry. 



" On the Incrustations which form in the Boilers of Steam- 

 Engines," in a letter addressed to Dr G. Wilson, F.R.S.E., 

 by Dr J. Davy. This communication will be found at page 

 250. 



Professor Voelcker then read a paper on the proportion of 

 phosphoric acid present in natural waters ; and the conclud- 

 ing one was by Professor Chapman on the isomorphous rela- 

 tions of silica and alumina. 



Section C. — Geology and Physical Geography. 



The first paper read was by Professor Hitchcock of N. 

 America, on the effects of river action in wearing down 



