4] 2 Mr. Greville Williams on Emeralds and Beryls. [June 19, 



riment was repeated in a modified manner several times. It having 

 been found that a faint turbidity in the lime-water was sometimes ob- 

 tained before the addition of the beryl, it was traced to the presence of 

 minute quantities of organic matter in the chromate and sulphuric acid. 

 To eliminate this source of error, the chromate and acid were mixed at 

 the commencement of the operation, and the current of air was kept up 

 until every trace of carbonic anhydride was removed ; at this point the 

 beryl was added, and the effect noted. The results, both with emeralds 

 or the beryl A, were, however, always precisely the same. 



The apparatus was then, recharged, and when half an hour's passage of 

 the air produced no milkiness in F, 5 milligrammes of charcoal were in- 

 troduced into D ; in two minutes the first bulb, and in four minutes all the 

 bulbs were rendered milky. 



In another experiment, after the usual precautions, 5 milligrammes 

 of graphite were acted on. In four minutes the first bulb, and in eight 

 minutes all three bulbs were rendered milky. 



The above experiments show, therefore, that the beryl A contains 

 carbon, not in the state of a carbonate, but in a condition which is more 

 slowly attacked than either free charcoal or graphite ; and it is, I think, 

 probably in the form of diamond, as has been shown to occur with the 

 carbon contained in artificially crystallized boron*. The power of free 

 chromic acid to attack the diamond with liberation of carbonic acid has 

 been shown by the Messrs. Rodgers f. 



The presence of carbon in beryls does not appear to be invariable. 

 After repeated experiments upon another large beryl from Haddam 

 County, North America, I was unable to satisfy myself that it contained 

 carbon. It is true that traces were found in the experiment ; but they 

 were so minute that they might have been due to the difficulty of entirely 

 excluding the presence of organic dust during the necessary manipu- 

 lations X • 



The next point I wished to ascertain was the relation borne by the 

 quantity of carbon in the beryl A to that in the emerald. For this 

 purpose I employed a similar apparatus to that used by Dumas in his 

 researches on the atomic weight of carbon previously alluded to. The 

 minute error due to the apparatus was carefully determined by going 

 through the whole process of heating the combustion-tube to redness for 

 the same time as in the analysis, the current of oxygen passing through at 

 the same speed, and finally replacing the oxygen in the system of tubes 

 by a current of pure dry air. No appreciable error was found to affect 



* Wohler and Sainte-Claire Deville, Comptes Rendus, February 16, 1857. 



t R. E. Rodgers and W. B. Rodgers, Chem. G-az. vol. vi. p. 356 (1848). 



\ Since the above paragraphs were written, an interesting paper has been published by 

 Prof. Silliman, " On the Probable Existence of Microscopic Diamonds with Zircons and 

 Topaz in the Sands of Hydraulic Washings in California," Chem. News, vol. xxvii. 

 p. 212. 



