254 ELEMENTARY GENERAL SCIENCE CHAP. 



EXPT. 264. Add a little water to the trioxide in the flask, 

 and test the liquid with litmus papers. 



The sulphur trioxide dissolves very readily in water, evolving 

 much heat and producing a hissing sound during solution. The 

 solution so obtained is strongly acid, being, in fact, sulphuric 

 acid. 



EXPT. 265. Heat the solution in an evaporating basin, and 

 also, at the same time, in another evaporating basin, heat 

 some dilute sulphuric acid, continuing the heating until thick 

 white fumes are obtained, and satisfy yourself the liquid is 

 sulphuric acid. 



Sulphuric acid. This very important compound, known also 

 as oil of vitriol, must be examined, as it is one of the most im- 

 portant and useful of chemical products, being of the greatest 

 service, not only in purely chemical operations, but also in various 

 industrial and manufacturing processes. 



It is a heavy, oily liquid, which, when strongly heated, boils 

 at 335 C., and gives off a quantity of choking, pungent, white 

 fumes, as has been observed in Expt. 265. It mixes with water 

 in all proportions, and produces during the solution so much 

 heat that the temperature may rise above 100 C., the boiling 

 point of pure water, so that care has to be taken when sulphuric 

 acid and water are mixed. It absorbs moisture from the air or 

 from moist gases, and on this account is very frequently used 

 for drying gases (Expt. 229), and, owing to the same affinity for 

 water, it chars organic matter, such as wood, &c. 



EXPT. 266. In a little strong sulphuric acid place small 

 pieces of wood, cloth, &c., and observe the effect. 



Like most other strong acids, it burns the skin and destroys 

 cloth, so that care must be always taken in its use. 



Action of Sulphuric Acid on Metals. Its action upon 

 metals has been already seen : with some metals, e.g., zinc, it 

 reacts when cold and dilute, liberating hydrogen and forming a 

 sulphate of the metal ; with others, e.g., copper, it has no action 

 until heated, when it produces a sulphate, but with the liberation 

 of sulphur dioxide. 



We can understand the latter action if we remember that the 

 sulphuric acid may be regarded as sulphur trioxide + water. 



