VOL. LXXXVIII.] 



PHILOSOPHICAL TRANSACTIONS. 



363 



figurse, multum lucis scientia expectat. Illae quarum antea compositionem explorare 

 licuit, naturali forma per artem privatse erant." It is not therefore an hypothesis 

 unworthy of examination which I advance, that gems derived from the rectangled 

 octoedra, whose specific gravity is above 3.300 to 3.800, will be found to be dia- 

 monds or octoedral rubies ; and these will be easily distinguished from each other, 

 by their lustre and hardness. Diamonds, whether red, yellow, blue, or white, 

 being hardest, though their specific gravity will be less ; viz. from 3.356 to 3.47 J, 

 as I found among different diamonds in my collection : whereas the octoedral ruby 

 was from 3.571 to 3.625, and inferior in hardness, not only to the diamond, but 

 to the corundum ; the specific gravity of which, in its different appearance of form 

 and colour, I found to vary from 3.876 to 4.166 ; and I suppose it to be subject to 

 a variation from 3.300 to 4.300: after which, the jargon will come, with a specific 

 gravity of 4.600 ; easily distinguished also, by its crystallization, from the above- 

 mentioned gems. The above specific gravities, Mr. Hatchett very obligingly 

 assisted me in taking, with his accurate scales, in the temperature of 60°. It will 

 not be understood that I depend entirely on the specific gravity ; on the contrary, 

 I connect this quality with crystallization : hardness is the next criterion ; and 

 analysis must separate the component parts, and demonstrate the analogy or identity 

 of substances, or of compounds. The improve- 

 ments of Mr. Klaproth's process are evident, by the 

 comparison of his first analysis, and his last analysis, 

 of corundum. In the first it consisted of 



Corundum earth 6*8. 



Siliceous earth . 3 1.50 



Iron and nickel 0.50 



100 

 Argillaceous earth 89.50 



By the last analysis of Klaproth, the corundum Oxideof Son .!!!!!!! ". ; \ '. '. 1.25 



Loss 3.75 



of the peninsula of India consisted of 



The Corundum of China. 



Argillaceous earth 84. 



Siliceous earth 6.50 



Oxide of iron 7*50 



Loss 2. 



100 



100 



That the analysis of sapphire by Mr. 



Klaproth may be compared, it is here 



added. 



Agillaceous earth 98.50 



Calx of iron 1 . 



Calcareous earth o.50 



100 



Iron ore crystallized is often mixed with the Chinese corundum, as I have before 

 stated, and may be considered as accidentally interposed, not combined. In the 

 corundum of the coast, the greenish colour may indicate the combination of iron 

 as the blue colour does in the sapphire; and the proportion of iron in both is nearly 

 alike. There then is the -~ and -~- of silex in corundum, evidently an integral 

 part of the coarse corundum crystal, and not of the sapphire ; but it will require an 

 analysis of the vitreous or pellucid corundum, to decide that silex is a constituent 

 part of corundum : there will then remain to account for the calcareous earth ; and 



3 a2 



