1820.J of different iiwrgaiik Bodies. 97 



oxygen of which ought to be 0-7725 + 3 x 2-3175, and the 

 sulphur, 1-5540. Of consequence, sulphuric acid is composed of 



Sulphur 40-1395 100-00 



Oxygen 59-8605 148-44 



Hence it follows that the capacity of saturation of sulphuric 

 acid ought to be '■ — — • = 19-9535. 



It is known by old experiments that sulphur in order to pro- 

 duce sulphurous acid must combine with two-thirds of the 

 oxygen which exists in sulphuric acid. Hence it is easy to cal- 

 culate the composition of sulphurous acid. I thought, however, 

 that a verification of this calculation furnished by the determina- 

 tion of the specific gravity of sulphurous acid would not be 

 superfluous. And though the experiments which I made with 

 this view have not given the I'esult which I expected, I shall 

 here give an account of them. 



If we suppose that oxygen gas when it unites with sulphur to 

 produce sulphurous acid preserves its volume just as when it 

 forms carbonic acid gas with carbon, it is evident that the differ- 

 ence between the specific gravity of sulphurous acid and oxygen. 

 gas ought to indicate the quantity of sulphur contained in the 

 former gas. I prepared sulphurous acid gas in the following 

 manner : I put copper into a retort, which I then filled com- 

 pletely with concentrated sulphuric acid. The beak of the retort 

 was then introduced into sulphuric acid, and the retort was, 

 heated till the gas extricated ceased to drive out sulphuric acid. 

 The beak of the retort was then plunged under a glass jar filled 

 with mercury, and the disengagement of sulphurous acid gas 

 was continued. The glass vessel had at its top a stop-cock of 

 brass, which could not be filled with mercury, and in which, 

 there remained of consequence a little atmospherical air. This 

 portion was removed by filling a sixth part of the vessel with, 

 sulphurous acid gas, and then throwing out this mixture of gas 

 and air. This operation was repeated five or six times before 

 the vessel was finally filled with sulphurous acid gas. This gas 

 was then introduced till the gas within the glass was compressed 

 hy a column of mercury, an inch in height, on the outside of the 

 vessel. I then adapted to it, by means of a stop-cock furnished 

 with a screw, a thin glass matrass, which 1 had previously 

 exhausted of air. Ou opening the stop-cock, the matrass was 

 ^led with sulphurous acid gas, and care was taken to plunge the 

 glass in the mercury till the gas in the matrass was somewhat 

 compressed. It was then carried to the place where it was to 

 he weighed. It was left there aa hour in order to acquire the 

 temperature of the place, which, was 59°. The stop-cock was 

 then opened, taking care not to touch the matrass with the hand^ 

 ia order not to alter the temperature. The gas being thus 

 brought into eciuilibrium with the air, the stop-cock was ?hut. 



Vol. XV. N" II. G 



