BUILDING STONES. 157 



Dolomites.] 



Smith, " a practical man well acquainted with the working of stone", con- 

 cludes with the following recommendation : 



"Having weighed, to the best of our judgment, the evidence in favor 

 of the various building stones which have been brought under our con- 

 sideration, and freely admitting that many sandstones as well as limestones 

 possess very great advantages as building materials, we feel bound to state 

 that for durability, as instanced in Southwell church, &c., and the results 

 of experiments as detailed in the tables ; for crystalline character, com- 

 bined with a close approach to the equivalent proportions of carbonate ot 

 lime and carbonate of magnesia; for uniformity in structure, facility and 

 economy in conversion, and for advantage of color ; the magnesian lime- 

 stone, or dolomite, of Bolsover Moor and its neighborhood, is, in our opinion, 

 the most fit and proper material to be employed in the proposed new Houses 

 of Parliament." 



This preference for magnesian limestones is confirmed by the physical 

 and chemical tests that have been conducted by the survey on the building 

 stones of Minnesota, and by observations made in numerous places on the 

 practical capacity of such stones to resist the action of the weather, as may 

 be witnessed by any one in the bold and precipitous escarpments of the 

 St. Lawrence limestone, as they appear in the bluffs of the Mississippi 

 river between Hastings and the Iowa boundary line. 



If the inquiry be pushed further, and some cause for the remarkable 

 durability of dolomites and dolomitic limestones be sought, it will doubtless 

 be found in the chemical nature of magnesia as compared with lime, or ot 

 carbonate of magnesia with carbonate of lime, or at least of dolomite as 

 compared with calcite. 



Maynesid as compared with lime. Magnesia, which is represented by the 

 chemical symbol MgO, is a compound of the metal magnesium and oxygen; 

 and lime, represented by CaO, is formed by uniting calcium and oxygen. 

 Either one may be obtained by the calcination of their carbonates, which 

 is performed in any ordinary lime-kiln. In the case of the production ot 

 quicklime from a magnesian limestone the magnesia and lime are intimately 

 connected. In the burning of pure limestone a pure quicklime is obtained. 

 In the former case the magnesia may be separated from the lime by dissolv- 

 ing them first in hydrochloric acid, and then adding a solution of soda or 



