SULPHURIC ACID. 325 



these acid vapours meet with the steam admitted near the same 

 point, and the formation of sulphuric acid takes place. The 

 nitric acid vapour is equivalent to nitric oxide or peroxide of 

 nitrogen, as the first effect of the sulphurous acid is to reduce 

 the nitric acid to a lower state of oxidation. From 8 to 1 9 

 parts of sulphur are consumed in the burner for 1 part of nitre 

 decomposed there, so that the quantity of nitrous fumes is 

 small compared with the quantity of sulphurous acid thrown 

 into the chamber. The chamber itself is 72 feet in length by 

 14 in breadth and 10 in height, and is divided into three com- 

 partments, by leaden curtains placed across it, two of which, 

 d and/, are suspended from the roof, and reach to within six 

 inches of the floor, and one e rises from the floor to within six 

 inches of the roof, g is a leaden conduit tube, for the dis- 

 charge of the uncondensible gases, which should communicate 

 with a tall chimney, to carry off these gases and to occasion a 

 slight draught through the chamber. The curtains serve to 

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

 manner through the chamber, so that the sulphuric acid is 

 deposited as completely as possible, before the vapours reach 

 the discharge tube. When the oxygen of the chamber is ex- 

 hausted, the admission of acid vapours is discontinued, till the 

 air in it is renewed. But the admission of air to the chamber 

 is sometimes so regulated, that a continuous current is main- 

 tained through the chamber, and the combustion proceeds with- 

 out interruption. When steam is admitted in proper quantity, 

 as in this method, it is not necessary to begin by covering the 

 floor with water, as the sulphuric acid is condensed with- 

 out it. 



The acid may be drawn off from the floor of the chamber of a 

 sp. gr. as high as 1.6. It is further concentrated in open leaden 

 pans, till it begins to act upon the metal and afterwards in 

 retorts of platinum or glass. It still retains small quantities of 

 nitrous acid and sulphate of lead, from which it can be com- 

 pletely purified by dilution with water and a second distillation. 

 The acid thus obtained in its most concentrated state is a defi- 

 nite compound of one atom acid and one atom of water, which 

 last cannot be separated by heat, the hydrate distilling over 

 unchanged. It is the oil of vitriol of commerce. 



Properties. Anhydrous sulphuric acid is obtained by 

 gently heating the fuming acid of Nordhausen in a retort, and 



