42 HOW CROPS GROW. 
Hydrogen forms with carbon a large number of com- 
pounds, the most common of which are the volatile oils, 
like oil of turpentine, oil of lemon, etc. The chief illumi- 
nating ingredient of coal-gas (ethylene or olefiant gas,) 
the coal or rock oils, (kerosene,) together with benzine 
and parafiine, are so-called hydro-carbons. 
Sulphur is a well-known solid substance, occurring in 
commerce either in sticks (brimstone, roll sulphur,) or as 
a fine powder (flowers of sulphur), having a pale yellow 
color, and a peculiar odor and taste. 
Uncombined sulphur is comparatively rare, the com- 
mercial supplies being almost exclusively of volcanic ori- 
gin; but in one or other form of combination, this element 
is universally diffused. 
Sulphur is combustible. It burns in the air with a pale 
blue flame, in oxygen gas with a beautiful purple-blue flame, 
yielding in both cases a suffocating and fuming gas of 
peculiar nauseous taste, which is called sulphurous acid. 
Exp. 15.—Heat a bit of sulphur as large as a grain of wheat on a slip 
of iron or glass, in the flame of aspirit lamp, for observing its fusion, 
combustion, and the development of sulphurous acid. Further, scoop 
out alittle hollow in a piece of chalk, twist a wire around the latter to 
serve for ahandle, as in fig. 3; heat the chalk with a fragment of sulphur 
upon it until the latter ignites, and bring it into a bottle of oxygen gas, 
The purple flame is shortly obscured by the opaque white fume of the 
sulphurous acid, 
Sulphur forms with oxygen another compound, which, 
in combination with water, constitutes common sulphuric 
acid, or oil of vitriol. This is developed toa slight ex- 
tent by the action of air on flowers of sulphur, but is pre- 
pared on a large scale for commerce by a complicated 
process. 
Sulphur unites with most of the metals, yielding com- 
pounds known as sulphides or sulphurets. These exist in 
nature in large quantities, especially the sulphides of iron, 
copper, and lead, and many of them are valuable ores, 
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