213 SOURCES OF AMMONIA. 



as if the substances which were the source of ammonia were 

 derived from the air, during the operation (Faraday). 



White clay from Cornwall, after being heated to redness and 

 exposed for a week to the air, yielded ammonia abundantly, when 

 heated in a tube. But when the clay was preserved in a good 

 stoppered bottle, after being heated to redness, this effect was not 

 produced. 



The observations which proved most undoubtedly that in all 

 these cases the ammonia was obtained from the air and condensed 

 on the surface of these materials, are the following (Faraday) : — 



Sea-sand was heated to redness in a crucible, and allowed tc 

 cool on a plate of copper; 12 grains of the sand were then 

 placed in a clean glass tube ; and an equal quantity, shaken upon 

 the hand, was allowed to remain there for a few moments, being 

 stirred about with the fingers, after which it was introduced into 

 a second tube by means of platinum foil, taking care that the 

 grains of sand were not brought in contact with any other animal 

 substance (Faraday). 



When the first tube was heated, it gave no sign of ammonia 

 to turmeric paper ; but the second tube did so in very appreciable 

 quantity. For the sake of precaution the tubes used in these 

 experiments were not cleansed by tow or cloth, but unused tubes 

 were taken, and before being employed they were heated to 

 redness in a stream of air (Faraday). 



Some asbestos heated to redness, and introduced into a tube 

 with metallic tongs, gave, when heated, no indication of ammonia ; 

 while, on the contrary, another portion, which had been simply 

 pressed with the finger, yielded immediate indications of am- 

 monia when heated in a tube (Faraday). 



Now it is known that ammonia evaporates by the skin, that 

 sweat contains salts of ammonia ; and nothing can be more certain 

 than that, in the experimenis last described, and also in those of 

 the burnt sand exposed to air, ammonia must have condensed on 

 the surface of the sand or of the asbestos. 



These experiments explain in a natural manner the existence 

 of ammonia in earth from which plants and animals are entirely 

 absent, and also of the formation of nitre in mixtures of earths 

 containing vegetable matter. 



