From the British and Tasmanian Iron Company. 49 



the iron is incorrect, but that at any rate, most, if not the 

 whole, of it is as two or more definite compounds of iron and 

 chromium diffused through the mass of iron. Different 

 portions of the same pig iron contain variable percentages of 

 these compounds. 



The sample of pig iron from which these results were ob- 

 tained gave 8-98 per cent, of chromium in one part, and 

 6*63 per cent, in another. 



Art. XIV. — Formation of Hyalite by the Action 

 of Ammonia. 



By J. Cosmo Newbery, B.Sc. 



[Read 12th December, 1878.] 



In the examination of building stones used in Melbourne I 

 have noticed that the greatest amount of decay takes place 

 during the summer months, December, January, and Feb- 

 ruary, and that the stones which harden on exposure harden 

 most during those months; also, that taking two portions of 

 the same stone, saturating one part with water, and leaving 

 the other dry, the wet stone hardens first, the hardening 

 taking place from the outside inwards. 



Analysis of the outer portions of these hardened stones 

 shows an excess of silica, more or less hydrous, and nearly 

 always giving distinct traces of ammonia. 



In the Geological Survey Reports, Nos. 4 and 5, I have 

 called attention to some of these peculiar passages of silica 

 from the inner to the outer parts of the stone, and shown 

 that all our freestones, except those already hardened by 

 exposure, are acted on with considerable rapidity by 

 ammonia and carbonate of ammonia. Some are hardened 

 by this action and some are disintegrated. Those which 

 are destroyed fall gradually away, the cementing material 

 being decomposed by the ammonia, and the quartz grains 

 are left free to faU or be washed away by the rain. 



In the stones which are not destroyed but harden, some 

 other action takes place ; the cementing material between 

 the sand grains is not softened, but it changes from a dull 



E 



