BOOK V. 



Ill 



schist, marble, and also in stone which easily melts in fire of the second 

 degree, and which is sometimes so porous that it seems completely decom- 

 posed. Lastly, gold is found in pjnites, though rarely in large quantities. 

 When considering silver ores other than native silver, those ores are 



Arsenical Minerals. Metallic arsenic was unknown, although it has been main- 

 tained that a substance mentioned by Albertus Magnus (De Rebus Metallicis) was the 

 metallic form. Agricola, who was familiar with all Albertus's writings, makes no mention 

 of it, and it appears to us that the statement of Albertus referred only to the oxide from 

 sublimation. Our word " arsenic " obviously takes root in the Greek for orpiment, which 

 was also used by Pliny (xxxiv, 56) as arrhenicum, and later was modified to arsenicum 

 by the Alchemists, who applied it to the oxide. Agricola gives the following in Bermannus (p. 

 448), who has been previously discussing realgar and orpiment : — " Ancon : Avicenna 

 " also has a white variety. Bermannus : I cannot at all believe in a mineral of a white 

 " colour ; perhaps he was thinking of an artificial product ; there are two which the Alchemists 

 " make, one yellow and the other white, and they are accounted the most powerful poisons 

 " to-day, and are called only by the name arsenicum." In De Naiura Fossiliiim (p. 219) is 

 described the making of " the white variety" by sublimating orpiment, and also it is noted 

 that realgar can be made from orpiment by heating the latter for five hours in a sealed 

 crucible. In De Re Metallica (Book X.), he refers to atiripigmentum faciicum, and no doubt 

 means the realgar made from orpiment. The four minerals of arsenic base mentioned by 

 Agricola were : — 



Orpiment (AS2S3) 



Realgar (As S) 



Artificial arsenical oxide 



Auripigmentum 

 Sandaraca 

 Arsenicum . . 

 Lapis suhrittilns atque 

 splendens 



Operment 



Rosgeel 



Arsenik 



Orpiment 

 Realgar 

 White arsenic 



Mistpuckel 



Arsenopyrite (Fe As S) *Mispickel 

 We are somewhat uncertain as to the identification of the last. The yellow and red sul- 

 phides, however, were well known to the Ancients, and are described by Aristotle, Theophrastus 

 (71 and 89). Dioscorides (v. 81), Pliny (xxxiii, 22, etc.) ; and Strabo (xii, 3, 40) mentions 

 a mine of them near Pompeiopolis, where, because of its poisonous character none but slaves 

 were employed. The Ancients believed that the yellow sulphide contained gold — hence 

 the name auripigmentum, and Pliny describes the attempt of the Emperor Caligula to extract 

 the gold from it, and states that he did obtain a small amount, but unprofitably. So late 

 a mineralogist as Hill (1750) held this view, which seemed to be general. Both realgar and 

 orpiment were important for pigments, medicinal purposes, and poisons among the Ancients. 

 In addition to the above, some arsenic-cobalt minerals are included under cadmia. 

 Iron Minerals. 



The classification of iron ores on the basis of exterior characteristics, chiefly hardness and 



