Annals of philosophy Volume 26 - Softcover

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1825-01-01 Excerpt: ..." It was then thought probable that the alkali might contain a minute quantity of some nitrous compound, or of a cyanide, introduced during its preparation. A carbonate of potash was therefore prepared from pure tartar, rendered caustic by lime calcined immediately preceding its use, the caustic solution separated by decantation from the carbonate of lime, not allowed to touch a filter or any thing else animal or vegetable, and boiled down in clean flasks; but the potash thus obtained, though it yielded no appearance of ammonia when heated alone, always gave it when heated with zinc. " The water used in these experiments was distilled, and in cases where it was thought necessary was distilled a second, and even a third time. The experiments of Sir Humphry Davy show how tenaciously small portions of azote are held by water, and that, in certain circumstances, the azote may produce ammonia. I am not satisfied that I have been able to avoid this source of error. " At last, to avoid every possible source of impurity in the potash, a portion of that alkali was prepared from potassium; and every precaution taken that could be devised for the exclusion of azote; yet, when a lamp was applied to the potash and zinc, the alkali no sooner melted down and mingled with the metal, than ammonia was developed; which rendered the turmeric paper brown, the original yellow re-appearing by the application of heat to the part. " Still anxious to obtain a potash which should be unexcep-. tionably free from any source of azote, I heated (says Mr. F.) a portion of potash with zinc, endeavouring to exhaust any thing it might contain which could give rise to the formation of ammonia: it was then dissolved in pure water, allowed to settle, the clear portion ...