338 Mr . Chenevix’s Analysis of Corundum | and of x 
Whenever I suspected that platina had been dissolved, I could 
easily detect the smallest portion of it. A solution of platina, so 
dilute as to be nearly colourless, manifests, in a very short time, 
the colour of a much more concentrate solution, and becomes 
reddish, by the addition of a solution of tin in muriatic acid. 
This I have found to be, by many degrees, the most sensible 
test for platina ; and it would answer the purposes of the Spanish 
government, much better than that they usually employ. 
The alkalis have no immediate action upon silver ; but I have 
observed, that crucibles of this metal, after they have been a 
long time in use, become somewhat more brittle than they were 
before. 
Potash and soda' have long been termed fixed alkalis ; and 
it is certain that, if we compare them with ammonia, they are 
so. Bu t fixed is an absolute term, and cannot admit of degrees. 
If potash, such as we obtain from Mr. Berthollet's method 
of preparing it, be kept in fusion at a very strong heat, it may 
be totally volatilized. The vapour of the alkali may be perceived 
in the room; and vegetable colours will undergo the change 
which is usually produced by alkalis. Indeed, in preparing Mr. 
Berthollet’s potash, the vapour of the alkali may be easily 
perceived. Soda is not quite so volatile ; though far from being 
fixed. It appears also, that a little water increases the volatility 
of both potash and soda, as happens with boracic acid. This 
volatility of potash, has been advantageously applied of late to 
the art of bleaching. 
