THE ASH OF PLANTS. 131 



nitric acid, and the sulphuric acid thus formed dissolves 

 in the water, and is afterwards boiled down to the proper 

 strength in glass vessels. 



The chief agricultural application of sulphuric acid is 

 in the preparation of " superpliosphate of lime," which 

 is consumed as a fertilizer in immense quantities. This 

 is made by mixing together sulphuric acid, somewhat 

 diluted with water, with bone-dust, bone-ash, or some 

 mineral phosphate. Commercial oil of vitriol is a mix- 

 ture of sulphuric acid with more or less water. The 

 strongest oil of vitriol commonly made, or " 66° acid," 

 contains 93.5% of H2SO4. The so-called "60° acid" 

 contains 77.6% H^SOi or 83% of 66° acid. Chamber 

 acid or "51° acid" contains 63.6% H2SO4, or 67% of 

 66° acid. 



Sulphuric acid occurs in the free state, though ex- 

 tremely dilute, in certain natural waters, as in the Oak 

 Orchard Acid Spring, of Orleans, N. Y., where it is pro- 

 duced by the oxidation of sulphide of iron. 



Sulphuric acid is very corrosive and destructive to most 

 vegetable and animal matters. 



Exp. 53. — Stir a little oil of vitriol with a pine stick. The wood is im- 

 mediately browned or blackened, and a portion of it dissolves in the 

 acid, communicating a dark color to the latter. The commercial acid 

 is often brown from contact with straws and chips. 



Strong sulphuric acid produces great heat when mixed with water, 

 as is done for making superphosphate. 



Exp. 64.— Place in a thin glass vessel, as a beaker glass, 30 c. o. of water ; 

 into this pour in a fine stream 120 grams of oil of vitriol, stirring all the 

 while with a narrow test-tube, containing a teaspoonful of water. If the 

 acid be of full strength, so much heat is thus generated as to boil the 

 water in the stirring tube. 



In mixing oil of vitriol and water, the acid should always be slowly 

 poured into the water, with stirring, as above directed. When water 

 is added to the acid, it floats upon the latter, or mixes with it but super- 

 ficially, and the liquids may be thrown aboxit by the sudden formation 

 of steam at the points of contact, when subsequently stirred. 



Sulphuric acid forms with the bases an important class 

 of salts — the sulphates, to be presently noticed — some of 

 which exist in the ash, as well as in the sap of plants. 



