176 Scientific Intelligence. 



the pyroligiiite spirit comes over first ; then follows the acetic acid^ 

 with water and empyreumatic oil, colorless, and tliere remains in 

 the retort a dark brown mass, similar to extract. — Ann. des Mines, 

 Tom. V. p. 78. 



16. JVeio method of discovering the presence of JVitric Acid, by 

 Just. Leibig. (Ann. de Chem. t. 35, p. 80.) — Mix the liquid to 

 be examined with as much indigo as is necessary to color it distinct- 

 ly blue ; add a few drops of concentrated sulphuric acid, and heat it 

 to ebullition. If the liquid contains a nitrate it is discolored, or if 

 the portion of nitrate is very small, its blue color changes to yellow. 

 In adding to the liquid a Uttle muriate of soda, prior to heating it, 

 we may easily detect the presence of ^^^ of nitric acid. — Idem. 



17. Reduction of Soracic Acid by Hydrogen ; by M. Varvinski. 

 (Fer. Bull. Tom. 10, p. 159.) — When hydrogen gas is passed 

 through a porcelain tube filled with boracic acid in scales, and heated 

 to redness, the acid is vitrified, and colored brown. If after this ope- 

 ration, it is treated witli boihng water, there remains a floculent and 

 olive colored substance, which is no other tlian boron. — Idem. 



18. On Pyrophorus ; by Gay Lussac. — (Ann. de Ch. t. 37. 

 p. 415.) — The causes to which pyrophorus owes its inflammation 

 not appearing to me sufficiently determined, I made the following 

 experiments : 



A mixture of calcined alum and calcined lampblack was heated in 

 an earthen retort. Carbonic acid and sulphurous gases are at first 

 disengaged, in nearly equal volumes ; then carbonic acid, pure, but 

 afterwards mixed with oxide of carbon, which in the end became 

 predominant. The remainder, vdien quite cold, inflamed like the 

 best pyrophorus, spreading a suffocating odour, of sulphurous acid, 

 and burning even with a slight blue flame. This pyrophorous is a 

 mixture of carbon, alumine, and poly-sulphuret of potassium, which 

 is formed at the expense of a part of the sulphuric acid, and sulphate 

 of alumine. 



The carbon is not indispensible to its formation ; for, by employ- 

 ing 75 gr. alum, and 3.33 gr. of calcined lampblack, I obtamed a 

 reddish brown matter, in which tliere remained no carbon, and which 

 was very inflammable. 



