with the nitrous vitriol. Although this method appears more troublesome, it allows the amount of nitre to be more easily and more accurately regulated. The size of the Glover towers, and more especially that of the Gay-Lussac towers, has been progressively increased, and thereby the cube of the lead chambers themselves has been diminished to a much greater extent. By improved
(From Thorpe's Inorganic Chemistry.)
Sulphuric Acid Plant.
A, Pyrites burners.
B, Nitre oven.
C, Glover tower.
D, Gay-Lussac tower.
E, Cooling pipes for Glover-tower acid.
F, F, F, Vitriol chambers.
G, Steam boiler.
H, Acid eggs or reservoirs for pumping the acid to top of towers.
I, Steam engine and stone-breaker for breaking up pyrites.
J, Chimney.
K, Engine for compressing air.
consideration is the form of the vessels; these may be open pans or dishes, or closed retorts, or combinations of both. We also note the Faure and Kessler apparatus, which consists of a platinum pan, surmounted by a double-walled leaden hood, in such a manner that, while the hood is constantly cooled from the outside by water, the thin acid condensing on its inside is carried away without being allowed to flow back into the pan. The majority of acid makers, however, prefer retorts made entirely of platinum, preferably provided by the Heraeus process with a dense, closely adherent coating of gold, including the top or “ dome.” The new Kessler furnace is a very ingenious apparatus, in which the fire from a gas-producer travels over the sulphuric acid contained in a trough made of Volvic lava, and surmounted by a number of perforated plates, over which fresh acid is constantly running down; the temperature is kept down by the production of a partial vacuum, which greatly promotes the volatilization of the water, whilst retarding that of the acid. This furnace is also very well adapted for impure acids, unsuitable for platinum or platinum-gold stills on account of the crusts forming at the bottom of the retorts; and it is more and more coming into use both in Great Britain and on the Continent. A third consideration is the condensation of the vapours formed in the concentrating process; the further the concentration proceeds the more sulphuric acid the contain. Condensation is a comparatively easy task in the case of, platinum apparatus, but with glass or porcelain beakers or retorts it presents great difficulties. In this respect the Kessler furnace has also proved to be very efficacious, so that it is at the present time considered the best apparatus for the concentration of sulphuric acid found in the trade. The highest strength of sulphuric acid practically attainable by boiling down is 98% H2SO4, and this is only exceptionally reached, since it involves much expenditure of fuel, loss of acid and wear and tear of apparatus. The usual strength of the O.V. of commerce, mostly designated by its specific gravity as 168° Twaddell, is from 93 to 95, or at most 96% HZSO4. When attempts are made to push the process beyond 98 % it is found. that the acid which distils over is as strong as that which remains behind. Real "' mono hydrate " or acid approaching 100 % can be made by Lunge's process of cooling strong O.V. down to -16° C. when H¢S0¢ crystallizes out, or by the addition of anhydrous S03 in the shape of fuming acid. Since the development of the Contact processes the fuming acid has become so cheap that it is now exclusively used for the preparation of the acids approaching the composition of “ mono hydrate." Fuming or Nordhausen Oil of Vitriol, a mixture or chemical compound of H¢S04, with more or less SOB, has been made for centuries by exposing pyritic schist to the influence of atmospheric agents, collecting the solution of ferrous and ferric sulphate thus formed, boiling it down into a hard mass (“ vitriol stein ) and heating this to a low red heat in small earthenware retorts. Since about 1800 this industry had been confined to the north-west of Bohemia, and it survived just till 1900, when it was entirely abandoned-not because its product had become any less necessary, but, quite 'on the contrary, because the enormously increasing demand for fuming sulphuric acid, arising through the discovery of artificial alizarine and other coal-tar colours, could not possibly be supplied by the clumsy Bohemian process. Other sources of supply had accordingly to be sought, and they were found by going back toareaction known since the first quarter of the 19th century, when ]. W. Diibereiner discovered the combination o S02 and 0 into S03 by means of spongy platinum. This reaction, now known by the name of the catalytic or contact process, was made the subject of a patent by Peregrine Phillips, in 1831, and was tried later in many ways, but had been always considered as useless for practical purposes until 1875, when it was simultaneously and independently taken up by Clemens Winkler in Freiberg, and by W. S. Squire and R. Messel in London. Both these inventors began in the same way, viz. by decomposing ordinary sulphuric acid by a high temperature into SOQ, 0, and H20 (the last of course being in the shape of steam), absorbing the water by sulphuric acid, and causing the S02 and 0 to combine to S05 by means of moderately heated platinum in a fine state of division. Winkler showed that this division was best obtained by soaking asbestos with a solution of platinum chloride and reducing the platinum to the metallic state, and he described later a specially active kind of “ contact substance, " prepared from platinum chloride at a low temperature. This revival of the synthetical production of S0, , at a period when this article had suddenly become of great importance, caused the greatest excitement among chemists and led to numerous attempts in the same direction, some of which were at once sufficiently successful to compete with the Bohemian process. It was soon found that the production of a mixture of S01 and O from sulphuric acid, as above described, was both too troublesome and costly, -and after a number of experiments in other directions inventors went back to the use of ordinary burner-gas from pyrites and sulphur burners. For a good many years the further development of this industry was surrounded by great mystery, but it is now known that a satisfactory solution of the difficulties existing in the above respect was attained in several places, for instance, at Freiberg and in London, by the labours of the original inventors, Professor' Winkler and Dr Messel. These difficulties were mostly caused by the solid impurities
