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 paraffin e, 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 a spirit lamp, for observing its fusion, 

 combustion, and the development of sulphurous acid. Further, scoop 

 out a little hollow in a piece of chalk, twist a wire around the latter to 

 serve for a handle, 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 to a 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. 



