THE VOLATILE PART OF PLANTS. 43 
Sulphides may be formed artificially by heating most of 
-the metals with sulphur. 
Expr. 16.—Heat the bowl of a tobacco pipe to a low red heat in astove 
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, 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 black sulphide of iron, in the same manner as in Exp. 7 it 
ourned 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 sulphides with dilute sulphuric 
acid, 
Exp. 17.—Place a lump of the 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 assafetida, 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 af 
