the Decomposition of the Earths, &c. 349 
of silex was long electrified, by degrees it lost its power of 
affording the substance in question.* 
This result having taken place, the same plan of operation 
was not pursued with respect to alumine, which resembles a 
saline compound less than silex, and the method which I now 
adopted of acting upon these bodies, was on the supposition 
of their being inflammable substances so highly saturated 
with oxygene as to possess little or no positive electricity. 
Alumine and silex have both a strong affinity for potash 
and soda ; now supposing them to be oxides, it was reason- 
able to conclude that the oxygene, both in the alkalies and 
the earths, must be passive as to this power, which must 
consequently be referred to their bases, and on this notion it 
was possible that it might be made to assist their decomposi- 
tion by electricity. 
After this reasoning, I fused a mixture of one part of silex, 
and six of potash in a platina crucible, and preserved the mix- 
ture fluid, and in ignition, over a fire of charcoal ; the crucible 
was rendered positive from the battery of five hundred, and a 
rod of platina, rendered negative, was brought in contact with 
* If silex that has been carefully washed, after precipitation by muriatic acid from 
liquor silicum, be moistened, and acted on by mercury negatively electrified, the 
mercury soon contains a notable quantity of potassium. Well washed alumine that 
has been precipitated from alum by carbonate of soda, affords by the same treat- 
ment sodium and potassium, so that the powers of electrochemical analysis are con- 
tinually demonstrating the imperfection of the common chemical methods of separating 
bodies from each other. The purest boracic acid which can be obtained from borax 
by chemical decomposition,.by electrical. analysis is shewn to contain both soda, and 
the decomposing acid employed in the process ; and hence the experiment on the 
action of the boracic acid and potassium, page 343, may possibly be explained 
without assuming its decomposition. 
