ALKALIES. 235 



7. SYNTHESIS. 



(a.) Hydrogen gas and nitrogen gas, mingled in the proper pro- 

 portions, do not form ammonia, nor would they ever do it their spe- 

 cific caloric opposes the union ; they would remain always a mere 

 mixture. 



(6.) Hydrogen in its nascent state, meeting with nitrogen, forms 

 ammonia ; this happens when hydrogen is disengaged from moistened 

 iron filings, included in a jar of nitrogen. 



(c.) Nitric acid, acting on tin or on phosphorus, forms ammonia ; 

 water furnishing the hydrogen and the acid the nitrogen ; it is then 

 disengaged by a little lime which arrests the acid, and the ammonia 

 is perceived by its odor, and by a white fume with muriatic acid.* 



(d.) Ammonia is formed during animal decomposition ; both its 

 elements being evolved from the animal matter, and uniting at the 

 instant ; this is the origin of ammonia in stables, privies, and other 

 similar places. 



8. ACTION ON COLORS. f 



(a.) Red tincture of alkanet becomes blue ; { blue infusion of cab- 

 bage, green ; diluted yellow tincture of rhubarb or turmeric, brown. 



* Ann. de Chim. et de Physique, XXIV. 295. 



t I am not aware that any reason has been suggested for these changes of color ; 

 certainly none has occurred to me that is satisfactory. As a general fact, permanent 

 changes of color depend on changes of composition, as is evinced in innumerable 

 cases ; for instance, red lead and red precipitate contain oxygen, a colorless body, 

 and metals, one of which is white and the other gray; indigo is intensely blue, 

 but becomes green by losing oxygen. In the case of the test colors, the color is 

 permanent, as long as the coloring matter is not decomposed, which happens event- 

 ually, and perhaps we may say that a peculiar combination takes place between the 

 coloring matter and the acid or alkali, although we can give no reason, any more thaa 

 in other cases, why these particular colors should result, or why there should be any 

 change of color. 



The autumnal hues of the leaves of trees probably depend on similar causes ; that 

 is to say, on the fuller developement of acid or alkali, by the variations of temperature ; 

 for these agents always exist abundantly in vegetable bodies, and particularly in their 

 fluids. It is not impossible that galvanic principles, may aid in producing and mod- 

 ifying the effects. 



If any person would examine the leaves of the sugar maple, for instance, just be- 

 fore the first autumnal frosts, and while they are still green, he could easily decide 

 whether acid or alkali were predominant, or whether either was to be found in a 

 state of freedom ; then let him examine the leaves after they have turned red, a color 

 which we should of course attribute to the developement of acid. A similar exa- 

 mination should be made of the chemical condition of leaves exhibiting other col- 

 ors produced by decay, as the yellow of the hickory, the brown of several species of 

 oak. &c. and so of the different colors observed in leaves of the same trees in the va- 

 rious stages of decomposition. 



In the American Journal, Vol. xvi, p. 215, there is a reference to an essay on this 

 subject, in the Ann. de Chim. et de Phys. Aout, 1828, in which it is stated, that the 

 colored parts of vegetables, appear to contain a particular substance, called by Prof. 

 De Candolle, chromule, and the autumnal change in the color of leaves is attributed 

 to the fixation of oxygen, and to a sort of acidification of the chromule. 



J We owe this very convenient test, to Dr. Hare. 



