The invention also comprises a novel process and apparatus for the concentration and refining of sulphuric acid for the above and other purposes, and the concentration and refining of other acids. The apparatus is illustrated in Figs. 82, 83, S4, and 85. According to this process air is heated to a temperature of about 700° in an iron coil ce, and distributed by means of pipes b, made of platinum, porcelain, or other material, into a closed vessel c, made of glass, glazed plumbago, or platinum. The hot air is introduced into the sulphuric acid in this chamber by means of the said perforated pipes or a perforated false bottom d, and the required draught through the apparatus is produced by an air-pump or aspirator, or other suitable means. Water has hitherto been used as the medium for condensing the waste fumes and for cooling the sulphuric acid after it leaves the still, but instead of water sulphuric acid is used for these purposes.
The condenser c, Figs. 82 and 83, is constructed with au outer casing e' and an inner box or ca,ing 0 of lead or other suitable material. Pipes f extend vertically through the said inner easing, and the latter is connected with the neck of the still or closed vessel e. The sulphuric acid used as
the condensing medium flows through the said pipes, and the air and gas from the closed vessel surronnd the same. g is a cock for drawing off the condensed liquid from the casing 0; h is a cooler or vessel for cooling tho liquid acid from the vessel e ; is a coil of pipe, and is a cock iu the The bottom of the retort or closed vessel c may be heated by the flame which heats the iron coil, tual the latter may servo as a support for the retort. Therefore the acid will be concentrated externally by the flame and internally by the hot air. The weak acid fumes are condensed and pumped to the top of the chamber used for the manufacture of sulphuric acid, and by means of an injector the coudenscd weak acid is distributed in the said chamber in the form of spray. This ellixts a saving of steam in the sulphuric acid chambers, and economizes the fuel used for concen tration by the use of the weak acid instead of water or steam.