1835.] Ascent of Chimborazo. 55 



We were at an elevation of 6004 metres (19,699 feet,) 

 which is I believe the greatest height that man has attained 

 on mountains. 



At 2 P M. the barometer stood at 371 '"'« 1 (13 inches 

 8J lines), the attached thermometer indicated a tempera- 

 ture of 7°-8 (46° F.) Under the shade of a rock the 

 detached thermometer stood at the same point. I en- 

 deavoured, but in vain, to find a cave in which I might 

 take the mean temperature of the station. At the depth 

 of one foot under the snow the thermometer stood at 0° 

 (32°), but the snow had melted and the instrument there- 

 fore indicated the temperature of the melted snow. 

 (To he continued.) 



Article VII. 



Examination of Hair Salt, or Native Sulphate of Alumina 

 and Iron. By Robert D. Thomson , M.D. 



The salt known under the name of hair salt and feather 

 alum, which is produced by the decomposition of strata 

 containing iron pyrites, has been examined by different 

 chemists; but hitherto no definite composition has been 

 assigned to it, notwithstanding the length of time which 

 has elapsed since it was first noticed. 



Dioscorides presents us with a detail of its characters so 

 striking as to prevent any mistake in identifying it.''^ He 

 describes it as being very white, astringent, in capillary 

 portiofts, whichTesemble what was called in Egypt trichitis. 

 Pliny likewise mentions it particularly : ** Concreti," says 

 he, " aluminis unum genus schiston appellant Graeci, in 

 capillamenta queedam canescentia dehiscens. Undequidem 

 trichitin potius appellavere. Hoc fit e lapide ex quo et 

 chalcitin vocant," &;c.J 



The indefatigable Tournefort visited the island of Milo, 

 from which the salt described by these ancient authors was 

 derived, and has satisfied us that the characters, as given 

 by Dioscorides and Pliny, are quite accurate.f 



1. Klaproth examined a salt of a greyish-white colour 



* V. 323, ijcvTTTTipia Tpt\tTLQ. X Plin. Nat. Hist. xxxv. 15. 

 t Tourneibrt's Voyage, i. 177. 



