•192 Scientific Intelligence — Mineralogy and Geology, 



animal economy, when they exist only in small quantity. Well- 

 water (of which a litre ?) contains only four to five centigrammes of 

 these substances in solution, may be employed for all domestic uses, 

 provided it does not contain too large a proportion of animal matter. 



3. Water, of which a litre contains one gramme of the above- 

 mentioned substances, may still be good for drinking; but it is not fit 

 for cooking vegetables or washing linen when it contains 01 gramme 



..of lime or magnesia. 



4. Water, of which a litre contains O'l gramme of lime or of 

 magnesia, and O'l gramme of organic matter, is improper for any 

 domestic use. 



5., It is of the utmost importance to state the existence, and de- 

 termine the quantity of animal matter held in solution in waters ; 

 for if they exceed the limits above stated, they act disastrously on 

 the economy, and may occasion dysentery, and various maladies which 

 appear to be contagious, because the whole population acquire the 

 seeds at the same sources. 



6. The presence of magnesia in drinkable waters does not pro- 

 duce so hurtful an action as supposed by some persons. The well- 

 water of Rhodez contains on an average five times as much magnesia 

 as the waters of the valley of the Iser, analysed by M. Granger ; 

 and yet endemic diseases,, as goitre and cretinism are entirely un- 

 known in the chief town of Aveyron. 



7. The water of certain wells possesses a very disagreeable earthy 

 taste; this taste is derived from alumina held in solution by car- 

 bonic acid. It is observed that those well-waters which contain 

 most of this base have the strongest earthy flavour. 



8. It results from these experiments, that a classification of drink- 

 able waters based on the relations which exist between the sulphates 

 and the chlorides, must be a defective one ; for this relation varies 

 with respect to the same kind of water, within limits of considerable 

 extent ; and it is never certain that the water operated on has not 

 met in its course either above or below the soil, with substances 

 which have altered and changed the proportions in which these salts 

 enter into its composition. — TJ Institute No. 851 ; Philosophical 

 Magazine^ vol. xxxvii., No 261, p. 395. 



MINERALOGY AND GEOLOGY. 



6. The extent of the coal area in Northumberland and Durham 

 is, in round numbers, 500,000 acres ; and, consequently, its total 

 contents amount to not less than 10,000,000,000 tons of coal, of 

 which 1,500,000,000 only have been worked. The present annual 

 consumption is estimated at 10,000,000, including the waste ; and 

 it consequently follows, that, at this rate, it would take above eight 

 centuries to exhaust this single field. 



