ON LAPIS PONDEROSUS 217 



The acid earth by itself produces some effervescence 

 with mineral alkali. With microcosmic salt it gives a 

 globule which is at first light blue, more of the acid makes it 

 dark blue, but it still remains free from redness .by refraction ; 

 with a further addition it becomes brown. Borax acquires 

 a slight tinge of blue, and with more of the acid becomes 

 of a yellowish brown colour ; but remains transparent, pro- 

 vided no further addition be made. 



This ultimate brown colour I have not been able 

 to drive off, either with nitre or the point of the 

 flame. 



A very easy method of distinguishing tungsten from all 

 other fossils hitherto known, is to pour upon it, when it 

 is reduced to powder, aquafortis or marine acid, and to set 

 the mixture in a digesting heat. It will soon be perceived, 

 especially when the latter acid has been employed, that 

 the powder gradually acquires a fine light yellow colour. 

 This happens not only with the species from Bitsberg, 

 but likewise with all the foreign sorts I have hitherto 

 had an opportunity of trying. What is usually called 

 white tin ore, in dusters like grapes, often belongs to this 

 species. 



With respect to the nature of the acid earth, it is nearly 

 allied to that obtained from molybdaena ; and both are in 

 a state much resembling that of white arsenic. It is well 

 known that arsenic, in its semimetallic state, is nothing 

 but a peculiar acid, saturated with phlogiston ; and that 

 the white calx is in an intermediate state between acid and 

 metal, containing just phlogiston enough to coagulate the 

 acid ; but remaining still soluble in water, and showing 

 signs of acidity. If a conclusion from analogy be admissible, 

 all the other metals should consist in a combination of the 

 same nature of the different radical acids, which, with a 



