316 Royal Society : — 



to redness in an atmosphere of oxygen, I felt it necessary to settle 

 this question definitely. With this intention I burnt 1-2 grm. of 

 beryl A in a platinum boat in a current of oxygen. The water 

 produced was received in a U-tube filled with fragments of asbestos 

 moistened with sulphuric acid. The carbonic anhydride was received 

 in a Greissler's potash-tube containing lime-water ; this form of 

 potash-tube was employed in this and the other experiments to be 

 described further on, as it enables the operator to see whether the 

 carbonic anhydride is all absorbed in the first bulb. The carefully 

 purified oxygen was allowed to stream through the lime-water for 

 half an hour to prove its freedom from carbonic anhydride. At 

 the end of that time there was no trace of turbidity. The beryl 

 was then heated to redness ; and in a few seconds the lime-water 

 in the first bulb of the potash-apparatus became milky, thus not 

 only proving the presence of carbon in a colourless beryl, but, 

 taken in conjunction with the quantitative determinations, showing 

 conclusively that the depth of colour is not, in this class of stones, 

 in the ratio of the amount of carbon present. 



But although demonstration had been obtained of the presence 

 of carbon in the beryl A, it was still possible that it might have 

 been derived from the decomposition of a carbonate. To settle this 

 question, I arranged an apparatus in the following manner : — 



A current of air from a gas-holder was sent in the direction 

 indicated by the arrow (see p. 317); it passed through a solution of 

 potassium hydrate in A and B. The three-necked bottle C contained 

 lime-water, freshly prepared and perfectly clear. The current of air 

 then passed into the three-necked flask D, containing 3 grms. of 

 beryl A, finely levigated in an agate mortar, and covered to about 

 one inch with pure distilled water. The flask E was empty, and 

 served to arrest any thing which might have spirted over. The 

 potash-apparatus F was filled to the height indicated with lime- 

 water. The pipette G contained concentrated sulphuric acid. The 

 arrangement being complete, a current of air was sent through for 

 half an hour ; not the slightest turbidity was found in C or F ; 

 the air was consequently free from carbonic anhydride. Its freedom 

 from any other substance containing carbon had been previously 

 determined by sending it mixed with oxygen, first into a red-hot 

 combustion-tube, and then into a previously weighed potash-appa- 

 ratus. After passage of the gas for half an hour, the potash- 

 apparatus was reweighed and found to be absolutely unaltered. 

 The purity of the air employed having thus been rigorously ascer- 

 tained, the stopcock of the pipette Gr was turned, and sulphuric 

 acid admitted into D until the water in the latter had become 

 very hot ; still no turbidity was observed in F. The fluid in D 

 was then boiled, with the same result. It was evident, therefore, 

 that the carbon found in the beryl was not derived from the decom- 

 position of a carbonate. The stopper at H was then removed, and 

 about 4 grms. of pure recently fused acid chromate of potassium 

 were added ; there was still no turbidity observed in F for twenty 

 minutes, during all which time the fluid in D was gently boiled. 



