184 Henry C. Richards: 



From a microscopical examination of thin sections of these 

 sandstones, the relative absorbent values may be determined, 

 particularly for the Bacchus Marsh, Darley, Egerton and 

 Greendale stones, as the amount of water absorbed varies almost 

 directly as the amount of fine-grained cementing matrix in the 

 stones. 



Unfortunately, the matrix is of an argillaceous character, so 

 that the high absorptions of these stones especially, must be 

 regarded as detrimental. 



Table of ABSORPTIo^'s in Percentages. 



4. — Resistance to Corrosion. 



The object of this test is to find out the effect on the stones, 

 of water containing carbon-dioxide in solution. Carbon-dioxide 

 occurs to the extent of about .04 per cent, in Melbourne air. 

 Rain water, carrying it in solution, is capable of dissolving 

 calcium, magnesium, and iron carbonates, so that any stones 

 containing these are affected by it. Limestones of course are 

 more severely acted on than other stones, but sandstones con- 

 taining these minerals are also affected. 



Two-inch cubes, smoothly dressed were thoroughly dried at 

 110 degrees C, cooled, weighed, and immersed in water, through 

 which a current of washed carbon dioxide was passed continu- 

 ously for three weeks. Precautions were adopted to keep a 

 quantity of the gas in contact with the water, so that it was 

 kept thoroughly saturated, and the water was changed every 

 few days. 



Along with the sandstones was placed a cube of Carrara 

 marble for comparison. 



