308 LECTURES TO SCIENCE TEACHEES. 



change, though many improvements in the working of the 

 various parts have been made. On the preceding page you 

 have a drawing of the old form of sulphuric-acid chamber, 

 whilst in Fig. 5 you find a bird's-eye view of a more 

 modern sulphuric acid works. These leaden chambers, of 

 which two are represented on the figure, are built of sheet 

 lead (seven pounds to the square foot), soldered together by 

 melting the edges of two adjacent sheets by means of the 

 oxy-hydrogen blowpipe. The chambers are supported on 

 a wooden framework, to which the leaden sheets are at- 

 tached by straps of lead, and the whole is raised some ten 

 or twelve feet from the ground by pillars of iron or brick- 

 work. In general, the whole erection is protected from the 

 weather by a roof, or at any rate by boards which serve to 

 keep off most of the rain. The sulphur or sulphur ore is 

 burnt in suitable ovens or kilns (aa\ and the gaseous 

 product is led, together with atmospheric air, into the 

 chamber, whilst ferric oxide (FeoOa) remains behind in the 

 kiln. For the purpose of obtaining the nitrous fumes, 

 which, as we have seen, are necessary for the process, 

 a small stove (b), containing nitre and sulphuric acid, is 

 placed in the central portion of the kiln. In this stove 

 the nitre is decomposed, an alkaline sulphate being left 

 behind, whilst the nitrous fumes evolved pass, together with 

 the other gases, into the chamber. Jets of steam are also 

 blown into the chamber at various points from a boiler (c), 

 and a thorough draft is maintained by connecting the end 

 of the second chamber with a high chimney not shown in the 

 drawing. The sulphuric acid as it forms falls on the floor 

 of the chamber, and when the process is working properly 

 it is continually drawn off as it attains a specific gravity of 

 1*55, or contains 64 per cent, of the pure acid, H 4 S0 4 , the 

 rest, 36 per cent., being water. In order to obtain an acid 

 stronger than this, further operations of concentration 

 and rectification must be performed. The acid of the 

 above strength, called chamber-acid, cannot be strengthened 

 in the chambers themselves, because an acid stronger than 

 this has the property of absorbing the red nitrous fumes, 

 whilst the weaker acid does not do so, and the presence of 

 such a strong acid would therefore effectually prevent the 

 further working of the chambers. That this is the case I 

 can readily show you. Here I have some strong sulphuric 



