186 Henry C. Richards: 



5. — Resistance to Acids. 



Ordinary city air contains small percentages of hydrochloric, 

 sulphuric, sulphurous, and nitric acids ; of these the hydro- 

 chloric and sulphuric are the most important. 



A solution containing 1 per cent, of each of these acids was 

 made up, and smoothly dressed two-inch cubes, after being dried 

 at 110 degrees C, cooled and weighed, were immersed in 300 

 CCS, of the solution, each in a separate beaker. 



The stones remained thus for a period of fourteen days, with 

 occasional turning over. At the end of this time they were 

 carefully removed, and allowed to drain for some time into the 

 beakers ; then, after being rinsed for several hours in a current 

 of water to thoroughly get rid of the acid, they were dried at 

 110 degrees C, cooled and weighed, and the loss in weight noted. 



The solutions were then made up to 500 cc, one portion being 

 used to determine the weight of the dissolved material as 

 chlorides and sulphates, and the other for the chemical analysis 

 of the dissolved material. 



During the test some material fell away mechanically, due to 

 the action going on between the matrix of the stone and the 

 acid. This was caught in a filter, ignited, and weighed. 



The effect of the acid on several of the stones was most pro- 

 nounced, especially on those from Barrabool Hills, Apollo Bay, 

 Darley. Sydney and Bacchus Marsh, while little or no change 

 took place in the 8tawell, Dunkeld, Egerton and Greendale stones. 



The Barrabool Hills stone was bleached to a much lighter 

 colour, and on fracturing the cube the alteration was visible up 

 to about 1.5 cm. below the surface, gradually becoming lighter 

 in colour outwards. 



The Apollo Bay stone underwent a very decided change in 

 colour, passing from a bluish-grey in the unaltered part to a 

 tint resembling very closely that of cement on the outside. On 

 fracturing the cube the zone of alteration was seen to be about 

 1.5 cm. wide, passing from the grey to a rather brown colour, 

 due to the oxidation of the ferrous iron in the stone. From this 

 point outwards there was a gradual loss of colour due to the 

 solution of the iron containing constituents, up to the cement 

 colour about 1 mm. wide at the surface. 



