52 Scientific Proceedings, Royal Dublin Society. 



in a glass tube containing air, and dropped into a tube containing 

 boiling mercury, lost nearly all colour after an hour's heating. 



Experiment 4. — Fragments sealed in a glass tube containing 

 air, and heated for five hours to a temperature of 180° 0. (in a 

 bath of boiling carbolic acid) suffered no change. 



Experiment 5. — Other specimens, heated by means of a sul- 

 phuric acid bath to a temperature of 200° C, rising to 250° for 

 about six hours, showed no change. 



Experiment 6. — Bits of green and yellow beryl placed in an air 

 bath, retaining a temperature of about 230° C. for thirty hours 

 showed a decided loss of colour. 



Experiment 7. — Boiling in water did not restore colour to the 

 decolourized specimens ; nor has it returned since (after forty 

 days). The specimens of experiments 2-7 retain translucency. 



Conclusions. — It appears from experiments 2 and 3 that a 

 temperature of 357° C. (the boiling point of mercury) is sufficient 

 to deprive both green and yellow beryls of colour in a very short 

 time, and that whether in contact with the air or not. Experiment 

 6 shows that the temperature of alteration may be taken, probably, 

 as well inferior to 350° C. ; with long-continued heating possibly 

 below 250° C. 



On the nature of the change effected in these beryls by heating 

 I am unable to give an opinion. Their continued translucency 

 shows at any rate that the change is not produced in a mechanical 

 way — as it might be — by the development of very numerous 

 cracks. 



I would suggest that this phenomenon bears on the history of 

 rocks containing this mineral. These green and yellow beryls to 

 be found nested far and wide throughout our Dublin granite are 

 in short so many maximum thermometers. Their delicate and 

 beautiful colours indicate a major limit to the changes of tempera- 

 ture experienced by the granite since their formation to the 

 present day. 



3. Altered Beryl. 



The third type, which may be described as altered beryl, includes 

 the larger portion of the total number of crystals coming from 

 Glencullen. I have found also similar crystals at Ballybetagh and 

 in Killiney granite. 



