57 



In other parts of the Same province this salt is 

 found with a calcareous base ; but we must not con- 

 sider as nitre all the salís which the inhabitants re- 

 present as such, for the natron is likewise found 

 there, or earthy alkaline salt, combined with sea 

 salt, and sometimes with the volatile alkali, to which 

 they improperly give the name of nitre. 



Besides common alum, and that called the plum- 

 ed,* which are found in many parts of Chili, a 

 semi-crystallized aluminous stoi:be has been disco- 

 vered in the Andes. This stone, called by the inhab- 

 itants polcura^ is brittle and of a pale white, of a 

 very fine grain and a vitriolic taste ; its external ap- 

 pearance is like that of white marble, but it contains 

 no calcareous particles, nor is it in reality any thing 

 but a clay saturated with vitriolic acid, analagous to 

 the aluminous stone of Tolfa. It is useful in dying, 

 and the quarries from whence it is procured com- 

 prehend a space of many leagues among the moun- 

 tains, which also aíFord another stone in some mea- 

 sure resembling it, but coarser and of much less 

 value. Its yellow hue, and the quantity of sulphur 

 and pyrites it contains, distinguish this last from the 

 real polcura^ which is very pure, and not combined 

 with any nietallic substance. 



The four principal kinds of vitriol, the green 

 or iron, the blue or copper, the white with a zinc 

 base, and the mixed, are found in a stalactite or 



* This name given to a sfiecies of talc^ consisting of 

 Jilamenrsj otherwise called the asbestos stone. — Dictionnaire de 

 l'Académie. 



Vol. i. K 



