292 Prof. Miller on some Crystallized Furnace Products. 



hydrogen nevertheless having a tendency to predominate ; the 

 reverse is the case with the other centres of emanationsj espe- 

 cially at Lago, where the proportion of hydrogen to the carbon- 

 ated gas attains 1 : 27. 



The presence of hydrogen in these emanations presents a new 

 feature of resemblance to the celebrated geysers and solfataras 

 of Iceland, and confirms the opinion previously expressed by one 

 of us. Bat the simultaneous existence of carbonated hydrogen 

 seems to differentiate the soffioni from the emanations of Iceland, 

 where, as is well known, M. Bunsen has never signalized the 

 latter gas. 



XXXI. On some Crystallized Fwnace Products. By W. H. 

 Miller, M.A., F.R.S., Professor of Mineralogy in the Uni- 

 vei'sity of Cambridge'^. 



Oxide of Zinc. 



O OME crystals of oxide of zinc, for which I am indebted to 

 ^ Dr. Percy, exhibit forms which have not been hitherto 

 correctly determined. The crystals belonged to the rhombohc- 

 di;al system. I observed the forms 111, 1 1 0, 4 2 3, 2 1, 

 3 11, and perhaps 4 2 1, the last symbol being rather doubtful 

 on account of the unevenness of the faces. One crystal appeared 

 to be cither a combination of the forms 110, Oil, 411, or 

 else a twin, the individuals of which are combinations of the forms 



110, Oil, having 111 for the twin face. This is probably 

 the combination observed by Descloizeanx {Ann. des Mines, ser. 4. 

 i. 482). I was unable to discover a trace of the form given upon 

 the authority of Koch, and denoted by the symbol a: a-.cc a : ^ c, 

 in Kammelsberg's most useful Handhuch der krystallograjihischen 

 Chemie, p. 28. _ 



The axis of the zone 111, 42 3, 20 1, 3ll, 421 makes 

 an angle of 30° with the axis of the zone Oil, 111,411. 

 A mean of twyity-four observed values of 2 1, 2 1 gave 



111, 2 1 = 42° 56'. The faces of the crystals were bright, 

 but extremely uneven. The measurements are therefore not capa- 

 ble of competing in point of accuracy with those of G. Rose {Das 

 krystuUochemische Mincralsystem, p. 64) and Schabus {Wiener 

 akad. Berichte, xi. p. 8). According to Rose, the value of 3 1 1, 

 3 1 T is between 52^ 17' and 52° 20'. Schabus found 3 1 1, 

 3 1 1=52° 17'"o. The angles computed from a mean of the 

 results obtained by Rose and Schabus are — 



* Communicated by the Author. 



