228 ANNUAL OF SCIENTIFIC DISCOVERY. 



aday remarked upon the " fur " which is formed in kettles and boilers, 

 often in great quantities. It consists of carbonate of lime, which is 

 deposited from the water by the process of boiling, and in some speci- 

 mens shown .was two or three inches thick. The inconvenience 

 arising from this accumulation may, however, be removed by the in- 

 troduction of muriate of ammonia, when the muriatic acid combines 

 with the lime, and forms a soluble product, which may be easily 

 washed out. London Mining Journal, June 1 . 



ON THE ACTION OF POROUS STRATA ON WATER AND ORGANIC 



MATTER. 



IT is a matter of immense importance to find from what source it is 

 best to obtain water for large towns, and how it is to be collected. 

 To these points Dr. Smith, in his report to the British Association 

 on the air and water in towns, particularly directs attention. Regard- 

 ing the conditions of many springs, which never become muddy, but 

 possess a constant brilliancy and a very equal temperature at all sea- 

 sons of the year, the author thinks that there is a purifying and cool- 

 ing action going on beneath. The surface water from the same place, 

 even if filtered, has not the same brilliancy or the same freedom 

 from organic matter, nor is it equally charged with carbonic acid or 

 oxygen gas. There are, therefore, other causes at work. The rain 

 which falls has not the purity, although it comes directly from the 

 clouds; it may even be wanting in cleanness, as is often the case. 

 Springs rise through a great extent of soil, and collect a considerable 

 amount of inorganic salts ; and it is shown by Dr. Smith that their 

 purity is due entirely to the power of the soil to separate all organic 

 matter, and at the same time to compel the mixture of carbonic acid 

 and oxygen. The amount of organic matter removed in this way is 

 surprising, and it is a most important and valuable property of the 

 soil. The change takes place even close, to cesspools and sewers; at 

 a very short distance from the most offensive organic matter, there 

 may be found water having little or none in it. As an agent for puri- 

 fying towns, this oxidation of organic matter is most extraordinary, 

 and we find the soil of towns which have been inhabited for centuries 

 still possessing this remarkable property. St. Paul's churchyard 

 may be looked upon as one of the oldest parts of London, but the 

 water from the wells around it is remarkably pure, and the drainage 

 of the soil is such, that there are very few, if any, salts of nitric acid 

 in it. " If the soil," says Dr. Smith, " has such power to decompose 

 by oxidation, we want to know how it obtains so much of its oxygen. 

 We must, however, look to the air as the only source, and see how it 

 can come from it. When water becomes deprived of its oxygen, it 

 very soon takes it up again, as may be proved by experiment. This 

 shows us that, as fast as oxygen is consumed by the organic matter, it 

 receives a fresh portion, conveyed to it by porous soil." Several ex- 

 periments of the following character were adduced, to show the filter- 

 ing power of the soil. A very dark solution of peaty matter was 

 made in ammonia ; this was filtered through sand, and came out per- 



