958 SULPHURIC ACID 



solution quickly becomes milky from the deposition of sulphur, the oxygen of the air 

 uniting with the hydrogen : 



HS + = HO + S (H'S + = H 2 + S). 



The principal use of sulphuretted hydrogen is in the laboratory for the separation 

 of certain metals from their solutions. Being much heavier than air, it can be poured 

 from one vessel to another. 



SULPHURIC ACID, Vitriolic Acid, or Oil of Vitriol. (Acid sulfurique, Fr. ; 

 Schwefels'dtire, Ger.). This important liquid now forms an extensive article of manu- 

 facture. It was formerly prepared by the distillation of sulphate of iron or green 

 vitriol, from which it received its name of oil of vitriol or vitriolic and. It was subse- 

 quently found that it might be produced by the combustion of sulphur, and the ultim- 

 ate further oxidation of the sulphurous acid, thus obtained, by the means of nitric acid ; 

 and from time to time improvements have been made in the process, until it is now 

 almost, perhaps entirely, perfect. 



In the first place the sxilphur is burnt on suitable hearths, and the sulphurous acid 

 produced is carried by flues, together with some nitrous and nitric acids, generated 

 in the same furnace from a mixture of nitre and sulphuric acid, into the large leaden 

 chambers, into which steam and air are also admitted ; here the different gases 

 react on each other, and the sulphurous acid becomes converted into sulphuric acid, 

 which falls into the dilute sulphuric acid which is placed in the bottom of the chamber, 

 which thereby becomes stronger, and, when of sufficient strength, is drawn off, and 

 concentrated first in leaden vessels, and finally in vessels of platinum. 



The place where the sulphur is burnt is a kind of furnace, but instead of the grate, 

 there is a stone hearth or iron plate, called the sole. The nitre-pot or pan is of 

 cast iron. In it the nitre is decomposed by the sulphuric acid, and it is placed in the 

 burner when required. The leaden chamber has the form of a parallelepiped, the 

 size varying with the amount of work required to be done. To produce 10 tons of 

 oil of vitriol weekly, the chamber should have a capacity of 35,000 cubic feet ; or n, 

 length of 187 feet, a breadth of 12J feet, and a height of 15 feet. The bottom is 

 covered to the depth of 3 or 4 inches with water acidulated with sulphuric acid. 

 These leaden chambers are sometimes divided into 3 or 4 compartments by leaden 

 curtains placed in them, which cause the more perfect mixture of the gases. Fig. 1943 

 is a drawing of one thus divided, taken from Pereira's ' Materia Medica.' 



1943 



On. OP 



a. Steam-boiler. 



b. Section of furnace of burner. 



it and/. Leaden curtains from the roof of the chamber to 'within six inches of the floor. 

 e. Leaden curtains rising from the floor to -within six inches of the roof. 



g. Leaden conduit or vent-tube for the discharge of uncondensible gases. It should communicate 

 with a tall chimney to carry off these gases, and to occasion a slight draught through the chamber. 



These curtains serve to detain the vapours, and cause them to advance in a gradual 

 manner through the chamber, so that generally the whole of the sulphurous acid is 

 converted into sulphuric acid and deposited in the water at the bottom before it 

 reaches the discharge pipes ; but as such is not always the case, there are sometimes 

 smaller chambers, also containing water, appended to the larger, from which they 

 receive the escaping gases before they are allowed to pass out into the air, and thus 

 prevent loss. These smaller chambers are seen in fig. 1944 c, d, also taken from 

 Pereira's ' Materia Medica.' 



Another method for preventing this loss was contrived by M. Gay-Lussac, and 

 made the subject of a patent in this country by his agent, M. Sautter. It consists in 

 causing the waste gas of the vitriol-chamber to ascend through the chemical cascade 

 of M. Clement Dosormos, and to encounter there a stream of sulphuric acid of specific 

 gravity 1 '750. The nitrous acid gas, which is in a well-regulated chamber always 

 slightly redundant, is perfectly absorbed by the said sulphuric acid ; which, thus im- 

 pregnated, is made to trickle down through another cascade, up through whicli passes 

 a current of sulphurous acid, from the combustion of sulphur in a little adjoining 

 chamber. The condensed nitrous acid gas is thereby immediately transformed into 

 nitrous gas (binoxide of nitrogen), which is transmitted from the second cascade into 



