110 REPORT 1861. 



burner. The smalls are then placed on a hearth of firebrick 40 feet long 

 and 6 or 7 feet wide, which is heated from below, and has a current of air 

 passing over it to burn the sulphur and convey the sulphurous acid into the 

 chambers. The material 's introduced at the end furthest from the fire, 

 where it only experiences a gentle heat, and is gradually moved forward to 

 where the heat is greatest. If the ore is ground, the sulphur may in this 

 kiln be completely burnt. We may mention, by the way, that the introduc- 

 tion of Spanish and Portuguese pyrites has caused the rise of a new branch 

 of industry in the extraction of the small quantity of copper which these 

 ores contain. The manufacturers do not, however, find it advisable in gene- 

 ral to extract the copper themselves ; they sell it to the smelter. 



The manufacturers of oil of vitriol have recently availed themselves of 

 anotlier source of sulphurous acid. In Hill's process of purifying gas, 

 hydrated peroxide of iron is employed instead of lime. After being used for 

 some time the material is exposed to the atmosphere, in order to re-oxidize 

 the reduced oxide of iron. The process is repeated thirty or forty time?, 

 after which it can no longer be employed for the purification of gas. It 

 contains, however, 40 per cent, of sulphur, and the manufacturers make use 

 of it in the same way as pyrites for the production of sulphurous acid. 

 From 1 ton of the material they obtain about 1^ ton of hydrated sulphuric 

 acid. 



Mr. Harrison Blair's improved sulphur-burner is especially valuable as 

 economizing space in the chambers, by preventing the sulphu'rous acid from 

 being diluted with too large an excess of air, as is the case with the ordinary 

 sulphur-burners. In this arrangement the sulphur falls into the burner 

 through a vertical hopper, air being admitted by an opening in front in suf- 

 ficient quantity to cause combustion of a portion of the sulphur, and by the 

 heat thus evolved to melt and volatilize the remainder. The vapour of the 

 sulphur is then supplied with a jet of air, from the side, carefully regulated, 

 and burns with a flame of great size. By means of this arrangement, one 

 chamber of a capacity of 25,000 cubic feet is stated to produce weekly 

 21 tons of rectified acid, whereas, by using the ordinary burner, a chamber of 

 the same capacity would produce only 11 tons. 



The tendency in this district has been to increase the size of the sulphuric- 

 acid-chambers. The largest that we have heard of has a capacity of 1 12,000 

 cubic feet. 



Many manufacturers employ Gay-Lussac's method, invented sixteen or 

 seventeen years ago for economizing nitric oxide. Pure sulphuric acid of 

 sp. gr. 1*75 is poured down a column filled with coke, so as completely to 

 moisten it. The waste nitrous fumes from the chambers, which would other- 

 wise be lost, are then passed through the column and absorbed. The liquid 

 is diluted with water to a sp. gr. of 1*50 and heated with steam, nitrous 

 fumes are evolved, which pass off into the chambers and are used instead of 

 fresh gas. By this means a saving of more than 50 per cent, of nitrate of 

 soda is effected. Others, however, do not employ this method, as they find 

 that with the present low price of nitrate of soda, £12 per ton, it does not 

 pay to collect and absorb the waste oxides of nitrogen. 



The use of platinum stills for the rectification of sulphuric acid has 

 been almost entirely abandoned, and their place supplied by glass retorts, 

 which are now made much larger and of better quality than formerly. They 

 are placed either over the naked fire, or else in iron pots containing a little 

 sand ; and when carefully protected from currents of air, the breakage is not 

 found to be excessive. The acid thus obtained is said to be more transpa- 

 rent and less coloured than that prepared with platinum. 



