Chemistry. 347 



ance of the exact nature and quantity of the food required 

 for the maintenance, in a healthy condition, of any of the 

 classes of our population. He established this by a variety 

 of most valuable tables, the importance of which was ac- 

 knowledged by various members of the Section. 



" On the Air and Water in Towns, and the Action of 

 Porous Strata on Water and Organic Matter," by Dr R. A. 

 Smith. — It is a matter of great 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 particularly 

 directs attention. Regarding the conditions of many springs, 

 which never become muddy, but possess a constant brilliancy 

 and a very equal temperature at all seasons of the year, the 

 author thinks that there is a purifying and cooling action 

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

 even if filtered, has not the same brilliancy ; it has not the 

 same freedom from organic matter, neither is it equally 

 charged with carbonic acid or oxygen gas, — there are other 

 influences therefore 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 con- 

 siderable 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 absorption of carbonic acid and oxygen. The 

 amount of organic matter removed in this way, by its com- 

 bination with oxygen, is surprising, and it is a most im- 

 portant and valuable property of the soil. The change 

 even takes place close to cess-pools 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 purifying towns, this oxidation of organic matter is the 

 most extraordinary, and we find the soil of towns which 

 have been inhabited for centuries still possessing this re- 

 markable power. St Paul's Churchyard may be looked upon 

 as one of the oldest parts of London, yet the water from the 

 wells around it is remarkably pure, and the drainage of the 

 soil is such that there is very little of any salt^of nitric acid 



