Mr. Greville Williams on Emeralds and Beryls. 319 



replacing the oxygen in the system of tubes by a current of pure 

 dry air. No appreciable error was found to affect the carbon-de- 

 termination ; but a correction had to be applied to the hydrogen. 

 The necessity for minute precaution will be evident when it is con- 

 sidered that 1 grm. of beryl A, or emerald, only yielded 3 milli- 

 grammes of carbonic anhydride. 



Estimation of Carbon and Hydrogen in Peruvian Emerald and Beryl A. 



I. 09725 grm. beryl A gave 00030 carbonic anhydride and 0*01 31 water. 

 II. 1-0082 „ „ „ 00031 „ „ 00174 „ 



III. 1-1690 „ emerald „ 0-0030 „ „ 0-0140 „ 



or, per cent. : — 



Lewy's 

 Emerald. Emerald 

 (mean). 



Carbonic anhydride 031 0-31 0-26 028 



Water 135 1-73 1-20 189 



In working on such minute quantities, it is not easy to speak 

 with certainty as to the proportion of hydrogen contained in eme- 

 ralds and beryls which is not due to the water present; and the 

 difficulty is increased by the fact, insisted upon by Boussingault*, 

 that these stones do not give off all their water below a red heat. 

 If it be considered permissible, which I cannot admit, to calculate 

 the hydrogen on the principle of deducting the water found on 

 ignition in a crucible from that formed during the combustion in 

 oxygen, and then calculating the percentage of hydrogen on the 

 difference, as Lewy has done, the results would be as follows : — 



Beryl A. Lewy's 



Emerald. Emerald 



I. II. (mean). 



Carbon 008 0*08 007 0-08 



Hydrogen 006 O'll 004 



The smallness of the values obtained, and even the very fact of 

 their close approximation, make me offer them with a certain 

 amount of reserve; and I shall endeavour to repeat them upon 

 much larger quantities as soon as I have found a method of avoid- 

 ing all possible sources of error. 



I have not inserted the numbers given by Boussingault, as there 

 appears to be some mistake in them. He found 0*24 per cent, of 

 carbon in the morallons, and yet says that this number agrees 

 with two of Lewy's determinations, one of which (he says) gave 

 0*21, and another 0*25 ; whereas I find, on reference to Lewy's 

 memoir, that that chemist obtained in the two experiments alluded 

 to 0*21 and 0*25, not of carbon, but carbonic anhydride. 



As it was possible that some of the carbon found in these expe- 

 riments might have been derived from the steel mortar used in the 

 preliminary crushing of the emeralds and beryls, I pulverized some 

 emeralds in a porcelain mortar, every precaution I could devise 

 being taken to prevent any contact of organic matter. On burning 



* Loc. cit. 



