INFLAMMABLES. 313 



Remark. According to Berzelius, a minute quantity of titanium 

 exists in the English acid, and of tellurium in that of Sweden. 



SULPHUROUS ACID. 



1. HISTORY. 



This gas being produced whenever sulphur is burned, it has proba- 

 bly always been known, although it was not recognized as a distinct 

 chemical agent, until noticed by Stahl ; but it was first obtained pure 

 by Dr. Priestley.* 



2. PREPARATION. 



(a.) In a glass globe or bottle, burn sulphur in common air, either 

 in a pendent spoon, f or by means of a sulphur match ; sulphurous 

 acid gas will be formed, and if there be litmus or cabbage infusion 

 in the bottle, it will be reddened, and eventually the color will be des- 

 troyed, 



(b.) The same result is obtained with oxygen gas ; the combus- 

 tion is brilliant, with a blue and white light, and the product is entire- 

 ly sulphurous acid. There is no change in the volume of oxygen 

 gas, but the weight is doubled. 



One volume of sulphur vapor unites with one volume of oxygen. 



(c.) Red oxide of mercury and sulphur, equal parts, or sulphur 

 12, and peroxide of manganese, 100 parts, mingled in powder 

 and heated, produce sulphurous acid gas; in the former case, one 

 cubic inch is obtained for every 5 grains of the oxide ; the latter pro- 

 cess is recommended as being a very good one. 



(d.) The best process is, by mercury 1 part, with 6 or 7J of sul- 

 phuric acid, in a small glass retort ; apply the heat of a lamp or of a 

 few coals, and obtain the gas over mercury, or by a recurved tube 

 passing to the bottom of a jar or bottle, and displacing the common 

 air, as exhibited in the figure on p. 232, only substituting an empty 

 bottle for the bottle of water theory, the mercury detaches 1 pro- 

 portion of oxygen, and leaves the whole of the sulphur combined with 

 the remaining two proportions of oxygen, and thus evolves the sulphu- 

 rous acid gas ; the sulphate of mercury which is formed, may be sav- 

 ed for future use. 



(e.) Sulphuric acid is decomposed by many other things ; it may 

 be boiled on charcoal, wood, straw, cork or almost any vegetable 



* On Air, Vol. II, p. 1. 



t Pendent spoons are easily made by cutting a slip of sheet copper, into the form 

 of a very acute isosceles triangle, the sharp end may be tlmist through a cork, and 

 the other be hammered into a spoon and turned at right angles. 



I Metal 2. acid 3. (Turner,) with so small a proportion of acid, there might be 

 danger of breaking the retort; it is better to use an excess of acid which can be af- 

 terwards poured off. Thenard directs 6 or 7 of acid to 1 of mercury. 



40 



