THE ELEMENTS OF PLANT FOOD 57 



sometimes mistaken for gold, and is therefore called 

 fool's gold. 



Some Compounds of S. Hydrogen sulphide (H 2 S), 

 sulphuretted hydrogen, is a gas of a disagreeable odor. 

 This substance is produced in the decay of vegetables 

 and animal matter and gives its most characteristic 

 odor to rotten eggs. It is present in most sulphur 

 springs. 



H 2 S and other sulphides act on most metals and tar- 

 nish them. Silver shows its effects quite noticeably. 

 If a rubber band is snapped around a silver dollar and 

 allowed to remain for a time, a black streak will appear 

 on the coin. This streak is caused by the sulphur in 

 the rubber uniting with the silver, thus producing silver 

 sulphide. This action of sulphur may be seen on silver 

 spoons used to dish boiled onions. Mustard and the 

 yolks of eggs also have a tarnishing effect on silver- 

 ware. 



The action of H 2 S on metals makes it one of the most 

 important reagents for use in the laboratory. It is 

 made from the metal sulphides by adding an acid. 



Ferrous sul- Hydrochloric Ferrous Hydrogen 



phide acid chloride sulphide 



FeS + 2HC1 = FeCl 2 + H 2 S 



The gas is poisonous, and when mixed with air is 

 explosive ; hence it should not be made where the gas 

 will enter the lungs or be allowed to escape into a 

 room where there is fire. 



Note. Sulphur is found about 100 feet below the surface in 

 Louisiana. A four-inch pipe is driven down to the bed of nearly 

 pure S. Another pipe leads superheated steam to the S, which is 

 thus melted and then forced by air pressure to the surface through the 



