960 SULPHURIC ACID 



extent, in Scotland. It is called, at Marseilles, the maladie des cluimbres. It may be 

 certainly prevented, by maintaining the interior of the chamber, by a jet of steam, at 

 a temperature of 100 Fahr. When these crystals fall into the dilute acid at the 

 bottom, they are decomposed with a violent effervescence, and a hissing gurgling 

 noise, somewhat like that of a tun of beer in brisk fermentation. 



The introduction of steam is a modern invention, which has vastly facilitated and 

 increased the production of oil of vitriol. It serves, by powerful agitation, not only 

 to mix the different gaseous molecules intimately together, but to impel them against 

 each other, and thus bring them within the sphere of their mutual chemical attraction. 

 This is its mechanical effect. Its chemical agency is still more important. By sup. 

 plying moisture at every point of the immense included space, it determines the 

 formation of hydrous sulphuric acid, from the compound of nitric, hyponitric, sul- 

 phurous, and dry sulphuric acids. 



Besides the process here described, which is called the continuous process, there was 

 another formerly adopted, called the intermittent process. This was also carried on 

 in large leaden chambers, but instead of a continuous stream of air, as passes into 

 the chambers, through the furnace by the continuous process, the chambers wero 

 opened now and then to introduce fresh atmospheric air. This process is, however, 

 now abandoned. 



By the continuous method, sulphuric acid may be currently obtained in the chambers, 

 of the specific gravity T35, or 1-45 at most ; but when stronger, it absorbs and retains 

 permanently much nitrous acid gas ; by the intermittent process, however, it may bo 

 obtained as dense as 1*550, or even 1-620 ; hence where fuel is high priced, as near 

 Paris, this method recommended itself by economy in the concentration of the acid. 

 In Great Britain, and even in most parts of France, however, where time, workmen's 

 wages, and interest of capital, are the paramount considerations, manufacturers do not 

 find it for their interest in general to raise the density of the acid in the chambers 

 above 1*400, or at most 1*500 ; as the further increase goes on at a retarded rate, 

 and its concentration from 1-400 to 1*600, in leaden pans, costs very little. 



For many purposes in the arts the acid, as it is taken from the leaden chambers, is 

 quite strong enough, and is employed under the name of ' Chamber Acid.' 



At about the specific gravity of 1-35, in Great Britain, the liquid of the chambers 

 is run off by the syphon above described, into a leaden gutter or spout, which 

 discharges it into a series of rectangular vessels made of large sheets of lead of 12 or 

 14 Ibs., to the square foot, simply folded up at the angles into 8 or 10 inches deep, 

 resting upon a grate made of a pretty close row of wrought-iron bars of considerable 

 strength, under which the flame of a furnace plays. Where coals are very cheap, 

 each pan may have a separate fire ; but where they are somewhat dear, the flame, 

 after passing under the lowest pan of the range, which contains the strongest acid (at 

 about 1-600), proceeds upwards with a slight slope to heat the pans of weaker acid, 

 which, as it concentrates, is gradually run down by syphons to replenish the lower 

 pans, in proportion as their aqueous matter is dissipated. The three or four pans 

 constituting the range are thus placed in a straight line, but each at a different level, 

 terrace-like. 



When the acid has thereby acquired the density of r650, or 1-700 at most, it must 

 be removed from the leaden evaporators, because when of greater strength it would 

 begin to corrode them ; and it is transferred into leaden coolers, or run through a long 

 refrigeratory worm-pipe, surrounded by cold water. In this state it is introduced into 

 glass or platinum retorts, to undergo a final concentration, up to the specific gravity 

 of 1-842, or even occasionally 1-845. When glass retorts are used, they are set in a 

 long sand-bath over a gallery-furnace, resting on fire-tiles, under which a powerful 

 flame plays ; and as the flue gradually ascends from the fireplace near to which it is 

 most distant from the tiles, to the remoter end, the heat acts with tolerable equality 

 on the first and last retort in the range. When platinum stills are employed, they 

 are fitted into the inside of cast-iron pots, which protect the thin bottom and sides of 

 the precious metal. The fire being applied directly to the iron, causes a safe, rapid, 

 and economical concentration of the acid. The iron pots, with their platinum 

 interior, filled with concentrated boiling-hot oil of vitriol, are lifted out of the fire- 

 seat by tackle, and let down into a cistern of cold water, to effect the speedy re- 

 frigeration of the acid, and facilitate its transvasion into carboys packed in osier 

 baskets lined with straw. Sometimes, however, the acid is cooled by running it 

 slowly off through a long platinum syphon, surrounded by another pipe filled with 

 cold water. Fig. 1945 shows a contrivance for this purpose. 



The under stopcock a being shut, and the leg b being plunged to nearly the bottom 

 of the still, the worm is to be filled with concentrated cold acid through the funnel c. 

 If that stopcock is now shut, and a opened, the acid will flow out in such quantity as 

 to rarefy the small portion of air in the upper part of the pipe b, sufficiently to mako 



