SULPHURIC ACID 



961 



1945 



the hot acid rise up over the bend, and set the syphon in action. The flow of the 

 fluid is to be so regulated by the stopcock a, that it may be greatly cooled in its 

 passage by the surrounding cold water in the 

 vessel /, which may be replenished by means of 

 the tube and funnel d, and overflow at e. 



The platinum retort admits of from four to 

 six operations in a day, when it is well mounted 

 and managed. It has a platinum capital, 

 furnished with a short neck, which conducts 

 the disengaged vapours into a lead-worm of 

 condensation ; and the liquid thus obtained is 

 returned into the lead-pans. Great care must 

 be taken to prevent any particles of lead from 

 getting into the platinum vessel, since at the 

 temperature of boiling sulphuric acid, the lead 

 unites with the precious metal, and thus causes 

 holes in the retort. These must be repaired 

 by soldering on a plate of platinum with gold. 



Sanitary motives alone induced the makers 

 of soda to condense their waste hydrochloric 

 acid in the first instance ; though they now dis- 

 cover its worth as a means of manufacturing 

 chloride of lime, and would not again return 

 to the nuisance-creating system if they might. 



The complicated changes which take place in 

 the leaden chambers during the conversion of 

 the sulphurous acid into sulphuric acid, were first 

 traced by M. Clement Desormes. He showed 

 that hyponitric acid and sulphurous acid gases 

 when mixed react on each other through the intervention of moisture ; that there 

 thence resulted a crystalline combination of sulphuric acid, binoxide of nitrogen, and 

 water. That this crystalline compound was instantly destroyed by more water, with the 

 separation of the sulphuric acid in a liquid state, and the disengagement of binoxide 

 of nitrogen ; that this gas re-constituted hyponitric acid at the expense of the atmo- 

 spheric oxygen of the leaden chamber, and thus brought matters to their primary 

 condition. From this point, starting again, the particles of sulphur in the sulphurous 

 acid, through the agency of water, became fully oxygenated by the hyponitric acid, 

 and fell down in heavy drops of sulphuric acid, while the binoxide of nitrogen 

 derived from the hyponitric acid, had again recourse to the air for its lost dose of 

 oxygen. This beautiful interchange of the oxygenous principle was found to go on, 

 in their experiments, till either the sulphurous acid or oxygen in the air was ex- 

 hausted. 



They verified this proposition, with regard to what occurs in sulphuric-acid 

 chambers, by mixing in a crystal globe the three substances, binoxide of nitrogen, 

 sulphurous acid, and atmospheric air. The immediate production of red vapours 

 indicated the transformation of the binoxide into hyponitric acid gas ; and now the 

 introduction of a very little water caused the proper reaction, for opaque vapours 

 arose, which deposited white star-formed crystals on the surface of the glass. The 

 gases were once more transparent, and colourless; but another addition of water 

 melted these crystals with effervescence, when ruddy vapours appeared. In this 

 manner the phenomena were made to alternate, till the oxygen of the included air 

 was expended, or all the sulphurous acid was converted into sulphuric. The residuary 

 gases were found to be hyponitric acid gas, and nitrogen without sulphurous acid 

 gas ; while unctuous sulphuric acid bedewed the inner surface of the globe. Hence, 

 they justly concluded their new theory of the manufacture of oil of vitriol to be 

 demonstrated. 



There are some points in the manufacture of sulphuric acid which require attention. 



1st. If the heat in the sulphur-furnace is too high, or when there is not a sufficient 

 supply of air, some sulphur sublimes, and is condensed in the chamber, and at last 

 falls into the sulphuric acid at the bottom of the chamber. By this means, not only 

 is less sulphuric acid produced, but the sulphuric acid, when drawn from the 

 chamber, contains some sulphur in suspension : in this case it must be allowed to 

 stand, so as to deposit the sulphur, which may be collected, washed, dried, and again 

 used. If the sulphur -were not removed before concentrating, it would, at the tem- 

 perature requisite for evaporation, decompose the sulphuric acid, with the escape of 

 sulphurous acid gas, and hence much sulphuric acid would be lost. The reaction that 

 would take place is represented by the following equation : 



VOL. III. 3 Q 



