Royal Society. 



315 



and concludes this small bleaching to arise from the destruction of 

 the crystalline character of the stone. I have carefully repeated and 

 extended these experiments. The emeralds employed were canu- 

 tillos from Santa Fe de Bogota ; they were kindly given to me by 

 Professor Church. The following values were obtained in a de- 

 termination of their specific gravity : — 



Specific gravity of 



Emeralds (Canutillos) before f 



usion. 



No. of experi- 

 ment. 



W. 



W. 



L 



pt. 



D. 



L 



II. 



III. 



4-4964 

 4-4961 

 1-6655 



2-8293 

 2-8294 

 1-0486 



o 



165 

 17-0 

 16-0 



•998921 

 •998841 

 •999002 



2-69 

 2-69 

 2-70 



The formula used was 



where 



W is the weight in air, 



W the weight in water, 



pt the specific gravity of water at t°, 



t the temperature of the water, 



D the specific gravity. 



One of the above emeralds was exposed for three hours in a pla- 

 tinum crucible to a bright reddish-yellow heat. At the end of the 

 operation it was rendered opaque on the edges, but the green colour 

 was not destroyed. This experiment completely confirms those of 

 Wohler and Eose and Hofmeister. It is, I think, quite evident 

 that no organic colouring-matter could withstand such a tempera- 

 ture for so long a time. The announcement by Lewy that the 

 depth of colour of emeralds is in proportion to the amount of 

 carbon present, made it at first appear improbable that colourless 

 opaque beryls would contain any of that element. The power of 

 the colouring-matter to resist a red heat having, however, made me 

 inclined to disconnect the question of the colour from that of the 

 presence of carbon, I made experiments to determine whether 

 beryls contained that element, and, if so, to what amount. An 

 experiment was made at this stage of the inquiry (see p. 319), the 

 result of which showed that the beryl analyzed* contained the same 

 amount of carbon as Lewy's emerald. As it was just possible that 

 the small increase in weight of the potash-tubes used by Lewy, Bous- 

 singault, and myself, in determining the carbon, might not have 

 been really due to the absorption of carbonic anhydride, but to some 

 volatile inorganic acid produced on heating the emeralds and beryls 



* As this beryl will be repeatedly alluded to in this paper, and especially 

 in the second part, I shall, for convenience of reference, call it " beryl A." It 

 was found in Ireland. 



