416 Mr. Greville Williams on Emeralds and Beryls. [June 19, 



described in this paper, hydrogen to possess advantages sufficient to coun- 

 terbalance the inconvenience of storing it in the large quantities required. 



The phenomena observed on submitting a fragment of beryl to the 

 action of the flame are very beautiful ; but to obtain the best results, 

 many precautions and some little practice are necessary. The coal-gas 

 having been lighted and the oxygen turned on, the beryl at once begins 

 to melt, and froths or, rather, boils violently. By careful regulation of 

 the supply of oxygen, the boiling entirely disappears ; but the slightest 

 excess of oxygen causes it to be renewed. This property of oxygen, 

 which is found to occur with other substances besides beryls and 

 emeralds, I hope to study in greater detail. Having so adjusted the 

 flame that the beryl fuses tranquilly, and is yet at the exact point of 

 maximum heat (if the substance is not too large for the apparatus), it no 

 longer lies as a shapeless mass on the carbon support, but gathers together, 

 rises up, and forms a perfect bead — round, clear, and brilliant. To 

 obtain the adjustment of position necessary for this result, it is indispen- 

 sable to wear very dark glasses, so dark, indeed, that objects can scarcely 

 be discerned through them in bright daylight. Without this precaution, 

 the minute details of the globule cannot be observed ; and it would be im- 

 possible to drive away the bubbles which form instantly when the bead 

 is moved in the slightest degree from the proper position. The heat and 

 glare would also soon seriously affect the sight ; and, with every precau- 

 tion, I have found, after the preparation of one or two hundred globules, 

 that my sight appears (even after an interval of some months) to be 

 slightly but decidedly deteriorated. If all is working properly, the bead 

 should be quite mobile ; and advantage of this must be taken to keep it 

 incessantly rolling, and yet not remove it from the point where it gives 

 out the most brilliant light. By this means the whole globule is ren- 

 dered transparent. If, on the other hand, it is allowed to remain with- 

 out motion on the carbon (unless the globule be very minute), it will be 

 found, when cold, to have a white opaque base, passing into the centre of 

 the bead in a conical form, and entirely destroying its beauty. This 

 exact adjustment of the position of the bead at the point of maximum 

 heat, combined with constant movement of the carbon support and 

 perfect regulation of the proportions of oxygen and hydrogen, are indis- 

 pensable to the production of the glasses, specimens of which accompany 

 this paper. 



"When thus fused, the globules obtained from the beryl A were clear 

 and colourless, but generally contained a few minute air-globules and 

 striae, which become obvious under the lens. Towards the end of this 

 part of the investigation I succeeded in almost entirely avoiding these 

 defects ; but I have been compelled for a time to abandon experiments 

 in this direction in consequence of the strain thrown upon the eyes. 



When chromic oxide is added to the beads, and they are again carefully 

 fused, they acquire a fine green colour; the tint, however, is infe- 



