THE VOLATILE PAET OF PLANTS. 27 



mon sulphuric acid, or oil of vitriol. This oxide is devel- 

 oped to a slight extent during the combustion of sulphur 

 in the air and the acid is prepared on a large scale for 

 commerce by a complicated process. 



Sulphur unites with most of the metals, yielding com- 

 pounds known as sulphides, or formerly as sulphurets. 

 These exist in nature in large quantities, especially the 

 sulphides of iron, copper, and lead, and many of them 

 are valuable ores. Sulphides may be formed artificially 

 by heating most of the metals with sulphur. 



EXP. 16. Heat the bowl of a tobacco-pipe to a low red heat In a stove 

 or furnace ; have in readiness a thin iron wire or watch-spring made 

 into a spiral coil ; throw into the pipe-bowl some lumps of sulphur, and 

 when these melt and boil, with formation of a red vapor or gas, intro- 

 duce the iron coil, previously heated to redness, into the sulphur vapor. 

 The sulphur and iron unite ; the iron, in fact, burns in the sulphur gas, 

 giving rise to a black iron sulphide, in the same manner as in Exp. 7 it 

 burned in oxygen gas and produced an iron oxide. The iron sulphide 

 melts to brittle, round globules, and remains in the pipe-bowl. 



With hydrogen, the element we are now considering 

 unites to form a gas that possesses in a high degree the 

 odor of rotten eggs, and is, in fact, the chief cause of the 

 noisomeness of this kind of putridity. This gas, com- 

 monly called sulphuretted hydrogen, or hydrogen sulphide, 

 is dissolved in, and evolved abundantly from, the water 

 of sulphur springs. It may be produced artificially by 

 acting on some metallic sulphides with dilute sulphuric 

 or hydrochloric acid. 



EXP. 17. Place a lump of the iron sulphide prepared in Exp. 16 in a cup 

 or wine-glass, add a little water, and lastly a little hydrochloric acid. 

 Bubbles of hydrogen sulphide will shortly escape. 



In soils, sulphur occurs almost invariably in the form 

 of sulphates, compounds of sulphuric acid with metals, a 

 class of bodies to be hereafter noticed. 



In plants, sulphur is always present, though usually in 

 small proportion. The turnip, the onion, mustard, horse- 

 radish, and assafoatida owe their peculiar flavors to vola- 

 tile oils of which sulphur is an ingredient. 



