Formation of Ammonia^ Si-c. 311 



crucible, and then poured out on to a copper-plate, and left 

 to cool : when cold, a portion of it (about 12 grains) was put 

 into a clean glass tube; another equal portion was put into 

 the palm of the hand, and looked at for a few moments, beino- 

 moved about by a finger, and then introduced by platina 

 foil into another tube, care being taken to transfer no animal 

 substance but what had adhered to the grains of sand : the 

 first tube when heated yielded no signs of ammonia to turme- 

 ric paper, the second a very decided portion. 



As a precaution, with regard to adhering dirt, the tubes 

 used in precise experiments were not cleaned with a cloth, or 

 to\v, but were made from new tube, the tube being previously 

 heated red hot, and air then drawn through it ; and no zinc 

 or potash was used in these experiments, except such as had 

 been previously tried by having portions heated in a tube, to 

 ascertain whether when alone they gave ammonia. 



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 tartai", rendered caustic by 

 lime calcined immediately preceding its use, the caustic solu- 

 tion 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 Avhen 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 nitrogen are 

 held by water, and that, in certain circumstances, the nitroo-en 

 may produce anmionia. 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 as the experiment made with it includes all the precau- 

 tions taken to exclude nitrogen, I will describe it rather mi- 

 nutely, as illustrative of the way in which the other numerous 

 experiments were made. A piece of new glass tube, about 

 half an inch in diameter, was first wiped clean, and then heat- 

 ed red hot, a current of air passing at the same time through 

 it ; about six inches in length was drawn off at the blow-pipe 

 lamp, and sealed at one extremity. Some distilled water was 

 put into a new glass retort, and heated by a lamp ; when about 



• Phil. Trans. 1807, p. 11. 



one 



