140 PRACTICAL LESSONS IN SCIENCE. 



This acid is a heavy corrosive liquid, colorless when pure, but 

 usually brownish from charred organic matter. It blackens 

 wood and cloth and almost every form of organic matter is ut- 

 terly destroyed by this powerful acid, even when much diluted. 

 If a few lumps of sugar be dissolved in a little water and mixed 

 with sulphuric acid, a violent action takes place and a black mass 

 of semi-solid substance results. Some varieties of shoeblacking 

 are made by the action of sulphuric acid on molasses or treacle. 

 Sulphuric acid has a strong affinity for water; if exposed to the 

 air in an open dish it soon absorbs water from the air so as to 

 greatly increase its bulk. It is frequently used in the laboratory 

 for drying substances without heat. 



A high degree of heat is developed by the action of sulphuric 

 acid on water, when the two are mixed, which leads one to sus- 

 pect chemical action. The diluted acid has a smaller bulk 

 than that occupied by the acid and water before mixing. The 

 corrosive action of this acid seems largely due to its power of 

 absorbing water from the objects with which it conies in con- 

 tact. 



Sulphuric acid acts on all the metals except gold and platinum, 

 and has a more powerful attraction for bases than any other 

 acid, displacing all other acids from their salts. Some bases 

 form two salts with sulphuric acid, as H 2 S0 4 +KOH KHS0 4 -f 

 H 2 0, acid potassium sulphate, and H 2 S0 4 +2KOK=K 2 S0 4 +2H 2 

 neutral potassium sulphate, while in the case of nitric acid only 

 one salt seems possible, as HN0 3 +KOH=KN0 3 +H 2 0. An acid 

 as sulphuric, which has the power to form two salts with one 

 metal, is called dibasic, while others that can form but one are 

 called monobasic. 



Sulphuric acid is one of the most important substances used in 

 manufacturing. It is used in making sodium carbonate, citric, 

 tartaric, acetic and nitric acids, sodium and magnesium sul- 

 phates, and various paints. It is used in calico printing, in dye- 

 ing, in gold and silver refining, in purifying oil and tallow. It is 

 used in medicine and is invaluable about the chemical laboratory. 



Hyposulphite of soda is a salt used extensively in photog- 



