1873.] Mr. Greville Williams on Emeralds and Beryls. 411 



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 an- 

 hydride. 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 con- 

 junction 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. 413) ; it passed through a solution of potassium hydrate 

 in A and B. The three-necked bottle C contained lime-water, freshly pre- 

 pared and perfectly clear. The current of air then passed into the three- 

 necked flask D, conta inin g 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 Gr 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 P; 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-apparatus. 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 ascertained, 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 decomposition 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. At the end of this .time a cloudiness 

 began to appear in the first bulb of F, and after half an hour in the 

 second bulb : finally, a decided precipitate was obtained ; it was collected, 

 washed, and on analysis proved to be carbonate of calcium. The expe- 



