26 HOW CROPS GROW. 



produced, it Is mingled with spray, to remove whioli it Is made to 

 stream through a tube loosely filled with cotton. After air has been 

 entirely displaced from the apparatus, the gas Is ignited at the up- 

 curved end of the narrow tube, and a clean bell-glass is supported over 

 the flame. Water collects at once, as dew, on the interior of the bell, 

 and shortly flows down in drops into a vessel placed beneath. 



In the mineral world we scarcely find hydrogen occur- 

 ring in much quantity, save as water. _ It is a constant 

 ingredient of plants and animals, and of nearly all the 

 numberless substances which are products of organic life. 



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 illu- 

 minating ingredient of coal gas (ethylene or defiant 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. 



XJncombiued sulphur is comparatively rare, the com- 

 mercial supplies being almost exclusively of volcanic ori- 

 gin ; but, in one or other form of combination, this ele- 

 ment 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 fum- 

 ing gas of peculiar nauseous taste, which is called sul- 

 phurous add gas or sulphur dioxide. 



Exp. 15.— Heat a bit of sulphur as large as a grain of wheat on a slip 

 of iron or glass, over the flame of a spirit lamp, for observing its fusion, ; 

 combustion, and the development of sulphur dioxide. Further, scoop 

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

 serve for a handle, as in Fig. 3 ; heat the chajk with a fragment of sul- 

 phur upon it until the latter ignites, and bring it into a bottle of oxygen 

 gas. The purple flame is sliortly obscured by an opaque white fume of 

 sulphur dioxide. 



Sulphur forms with oxygen another compound, the tri- 

 oxide, which, in combination with water, constitutes com- 



