corroded by the nitrous acid, whereby 
the folution acquires a turbid opal-like 
appearance, and a jelly-like confidence, 
which difagreeable circumftance cannot 
well be corrected. But if a turbidnefs 
appears in precipitating the tin by zinc 
from the marine acid, it is very foon re¬ 
moved by adding fome drops of marine 
acid. 
§ 5 - 
By repeated experiments according to 
this method I have found that in fimilar 
pieces of this ore there is no confiderable 
difference with refpedl to the proportion 
of its conftituent parts. But in pieces of 
a different appearance, the break of which 
is of a darker colour, and without luflre, 
♦ 
I found a more confiderable portion of 
iron. 
I diffolved half an ounce of this ore in 
aqua regia, and two different precipitates 
were 
