THE ASH OF PLANTS. 115 



its compounds have also been briefly alluded to, but re- 

 quire more detailed notice. 



Sulpliydric Acid, Sym H 2 S, mo. wl. 34. This substance, fa- 

 miliarly known as sulphuretted hydrogen, occurs dissolved in the water 

 of numerous so-called sulphur springs, as those of Avon and Sharon, N. 

 Y., from which it escapes as a fetid gas. It is not unfrequently emitted 

 from volcanoes and fumaroles. It is likewise produced in the decay of 

 organic bodies which contain sulphur, especially eggs, the intolerable 

 odor of which, when rotten, is largely due to this gas. It is evolved 

 from manure heaps, from salt marshes, and even from, the soil of moist 

 meadows. 



The ashes of plants sometimes 3 7 ield this gas when they are moisten- 

 ed with water. In such cases, a sulpJiide of potassium or calcium has been 

 formed in small quantity during the incineration. 



Sulphydric acid is set free in the gaseous form by the action of an acid 

 on various sulphides, as those of iron, (Exp. 17,) antimony, etc., as well as 

 by the action of water on the sulphides of the alkali and alkali-earth metals. 

 It may be also generated by passing hydrogen gas into melted sulphur. 



Sulphuretted hydrogen has a slight acid taste. It is highly poisonous 

 and destructive, both to animals and plants. 



Sulphurous Acid, Sym. SO 2 , mo. wt. 64. When sulphur is 

 burned in the air, or in oxygen gas, it forms copious white suffocating 

 fumes, which consist of one atom of sulphur, united to two atoms of 

 oxygen; S 2 , (Exp. 15.) 



Sulphurous acid is characterized by its power of discharging, for a time 

 at least, most of the red and blue vegetable colors. It has, however, no 

 action on many yellow colors. Straw and wool are bleached by it in the 

 arts. 



Sulphurous acid is emitted from volcanoes, and from fissures in the 

 soil of volcanic regions. It is produced when bodies containing sulphur 

 are burned with imperfect access of air, and is thrown into the atmos- 

 phere in large quantities from fires which are fed by mineral coal, as well 

 as from the numerous roasting heaps of certain metallic ores, (sulphides,) 

 which are wrought in mining regions. 



Sulphurous acid may unite with bases, yielding salts known as sul- 

 phites, some of which, viz., sulphite of lime and sulphite of soda, are em- 

 ployed to check or prevent fermentation, an effect also produced by the 

 acid itself. ^ 



Anhydrous* Sulphuric Acid, Sym. SO 3 , mo. wt. 80, is 



known to the chemist as a white, silky solid, which attracts 

 moisture with great avidity, and, when thrown into water, 

 hisses like a hot iron, forming the hydrated sulphuric acid. 



* i. e., free from water. 



