168 Scientific Proceedings, Royal Dublin Society. 



Fusibility.— Compared with authentic harmotome on the mel- 

 dometer it was found that the fusion of both occurred simultane 

 ously at a very high temperature. The specimens also blanched 

 below a red heat. It was interesting to compare this behaviour 

 with that of some other zeolites. The result is the following order 

 of fusibility with increase of temperature : — 



Chabasite \ 



Stilbite [ almost simultaneously. 



Heulandite ] 



Natrolite 



(Orthoclase) 



Harmotome. 



Harmotome is, in fact, separated from the others by a wide 

 interval. Orthoclase fuses in this interval, and, indeed, decomposi- 

 tion or ebullition of the orthoclase takes place before the melting- 

 point of harmotome is reached. Recent experiments gave me for 

 the melting-point of orthoclase the temperature of 865° 0. It is 

 likely that the fusion of harmotome does not occur under 900° C. 

 I had not time to go through with the measurement independently. 

 I would point out, however, that there is very little liability to 

 error in comparing the fusibilities of two substances, placed thus 

 under exactly the same conditions and observed simultaneously in 

 the field of the microscope. On the other hand, not only is the 

 blowpipe a powerful chemical agent, and thus obscures the pheno- 

 mena of fusion with secondary effects, but with it it is impossible to 

 be sure of fair comparison. The meldometer has shown me that 

 the order of Van Kobel's scale is incorrect. Thus the order it 

 assumes for the fusibilities, almandine, green actinolite, orthoclase, 

 should be orthoclase, green actinolite, almandine ; and it is, I think, 

 allowable to assume that similar misleading phenomena account for 

 the fusibility of harmotome being recorded as 3*5 on the scale of 

 Yan Kobel. The test of fusibility, like that of sp. gr., is thus a 

 distinctive one in the case of harmotome. 



A test of its hardness showed that it scratches fluorite, and is 

 scratched by apatite; hardness, therefore, 4'5. In the blowpipe it 

 fuses without intumescence. 



It does not gelatinize with, but is decomposed by, hydrochloric 

 acid. These tests confirm its identity with harmotome. 



