1825.] On the Formation of Ammonia, $c. 145 



ing, were found to be essentially requisite, in consequence of 

 the delicacy of the means afforded by heat and turmeric paper 

 for testing the presence of ammonia, or rather, of matter con- 

 taining its elements. As a proof of this, it may be mentioned, 

 that some sea sand was heated red-hot for half an hour in a 

 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, being moved 

 about by a finger, and then introduced by platina foil into an- 

 other 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 turmeric 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 

 tow, 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 ascer- 

 tain 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 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 anything 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 nitrogen are held by 

 water, and that in certain circumstances the nitrogen 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 pot 

 * Phil. Trans. 1807, p. 11. 



L 



