188 ESSAY XV. 



of Glauber's salt, and hung it up for some weeks in the 

 cellar. The result was that the fossil alkali effloresced on 

 its surface like wool. The same thing happened upon 

 repeating the experiment with a solution of cubic nitre ; 

 but when I used plates of lead, tin, copper, or silver, no 

 decomposition took place. I afterwards prepared a mass, 

 consisting of unslaked quicklime moistened with a solution 

 of common salt, arid placed it in a moist cellar ; in a fort- 

 night afterwards the surface was covered over with mineral 

 alkali, which I scraped off, and left the remainder in the 

 cellar. In another fortnight more alkali was visible on the 

 surface, which was scraped off. Water was poured on the 

 remaining mass, and it was well stirred and filtered. The 

 solution had a strong taste of lime-water, on which account 

 I let it stand a few days in the open air, by which means 

 the lime was precipitated. And to determine with more 

 certainty whether the lime was all precipitated, I poured on 

 it a solution of corrosive sublimate, which remained colour- 

 less. The whole was then filtered, and a solution of the 

 efflorescent mineral alkali added to it, by which a Consider- 

 able quantity of aerated lime was precipitated. 



In the same manner I made a mass of quicklime and 

 solution of Glauber's salt and cubic nitre, when the same 

 effect was produced, and an efflorescence of fossil alkali was 

 observed. But this did not happen when, instead of quick- 

 lime, aerated or calcined magnesia or aerated lime were used 

 instead of unslaked lime. 



It is certain that fossil alkali always precipitates solu- 

 tions of iron and lime ; and it is a consequence of this that 

 fixed alkalies more readily combine with acids than these 

 substances. The experiments, however, which I have related, 

 point out a limitation in certain cases. It is therefore 

 probable that alkalies have a stronger attraction for acids 



