THE VOLATILE PAET OF PLANTS. 43 



Sulphides may be formed artificially by heating most of 



the metals witli 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 watcli-sprini; mcide into 

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

 these melt and boil witli formation of a red vapor or gas, introduce 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, giv- 

 ing rise to a blaclc sulphide of iron, in the same manner as in Exp. 7 it 

 Durned in oxygen gas and produced an oxide of iron. The sulphide of 

 iron 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, which is, in fact, the chief cause of 

 the noisomeness of this kind of putridity. This substance, 

 commonly called sulphuretted hydrogen, also sulphydric 

 acid, is dissolved in, and evolved abundantly from, the 

 water of sulphur springs. It may be produced artificially 

 by acting on some metallic sidphides with dilute sulphuric 

 acid. 



Exp. 17. — Place a lump of tlie sulphide of iron prepared in Exp. 16 in 

 a cup or wine-glass, add a little water, and Lastly a few drops of oil of 

 vitriol. Bubbles of sulphuretted hydrogen gas 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 quantity. The turnip, the onion, mustard, horse- 

 radish, and assafcetida, owe their peculiar flavors to volatile 

 oils in which sulphur is an ingredient. 



Albumin, gluten and casein, — vegetable principles never 

 absent from plant or animal, — possess also a small content 

 of sulphur. In hair and horn it occurs to the amount of 

 3 to 5 per cent. 



When organic matters are burned with full access of 

 air, their sulphur is oxidized and remains in the ash as 

 sulphuric acid, or escapes into the air as sulphurous acid. 



Phosphorus is an element which has such intense s£- 



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