54 2 STUDIES FOR STUDENTS 



were performed would permit, it was demonstrated that the 

 strength of the sandstone, which had a high percentage of pore 

 space, was less affected by freezing and thawing than the strong 

 granites and limestones having a low percentage of po-re space. 

 It was naturally thought that the Dunnville sandstone, which 

 has 28.28 per cent, of pore space, and consists of relatively fine 

 particles, would experience a greater loss in strength than any 

 of the other rocks tested. The results, however, give evidence 

 that a rock as fine-grained and poorly-cemented as this, with 

 pore spaces which are little greater than sub-capillary size, is 

 but slightly injured by alternate freezing and thawing. 



It has been a matter of frequent observation that limestone 

 and marble suffer more by hard freezing immediately after 

 being taken from the quarry than other stones which have a 

 higher porosity. This has usually been spoken of as excep- 

 tional, but I venture to say that between limestone, marble, and 

 sandstone, the two former can furnish more examples of injury 

 by freezing of interstatial water than the latter. A reasonable 

 explanation for this result would be that the pore spaces in the 

 limestone are usually of sub-capillary size, while those in the 

 sandstone are mainly of capillary size. 



EFFECTS OF SULPHUROUS ACID GAS 



Limestone, dolomite, and marble are the only stones which 

 are to any extent injured by sulphurous acid gas. Eleven samples 

 of limestone and dolomite from as many different quarries were 

 exposed for forty-four days to sulphurous acid gas in a moist 

 atmosphere. Some of the pieces of limestone were colored 

 yellow, others were slightly etched on the surface, while many 

 of the samples showed a glistening precipitate of magnesium 

 salts. By washing the samples the magnesium salt was taken 

 into solution and through this the weight of the sample was 

 slightly decreased. 



The deterioration of limestone or dolomite in a moist atmos- 

 phere laden with sulphurous acid gas is apparently not very 

 rapid. Where deterioration does not proceed very rapidly under 



