In September, 1807, our illustrious chemist applied his great principle to the analyses of potash, the vegetable alkali. Some had supposed it to consist of lime and hydrogen; others conjectured that it might contain nitrogen; and Mr Davy himself conceived that it might consist of phosphorus, or sulphur united to nitrogen. After failing with strong aqueous solutions, and also with dry potash, from its being a non-conductor, he employed fused potash, and in this case inflammable matter was separated by the voltaic influence. He then tried 'a piece of potash moistened, and in this instance inflammable matter was developed.' On the 6th of October he found that the 'matter instantly burned when it touched water, and swam on its surface, reproducing potash.' In dry oxygen gas likewise it burnt into 'perfectly dry potash.' In like manner, Mr Davy succeeded in decomposing soda; and when he had thus proved that the two fixed alkalis were metallic oxides, he immediately supposed that the earths, which were so much more like to metallic oxides than the fixed alkalis, would be easily decomposed.