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pliurous acid became less and less, till its lowestpoint was reached at 120 feet, where it was 13 per,cent.
In the experiments at 3 feet from the bottom thedifferences are not so great as at 15 feet from thebottom, the latter being more affected by the steamentering the chamber, which, as far as could bedetermined, was equal to about one-quarter of themixed gases. This result appears to show that theupper portion of the chamber is chiefly used as areservoir for sulphurous acid, whence it descendsto the working portion of the chamber, next the acidat the bottom, for condensation as sulphuric acid.This was checked in another way, by placing a col-lector in the chamber at 4 feet from the bottom,and at 16 feet from the bottom. From the formerthere was a regular and fairly large make of acid;but from the latter there was scarcely any produc-tion, there being oidy one-sixteenth of an inch afterstanding nine days.
(2). Sulphuric Acid , 3 feet from bottom .—Beginningat 10 feet from the entrance the acid was 81 percent., then a sudden rise brings it to 89 per cent, at20 feet from the entrance, after which the per-centage falls regularly till at 100 feet the quantityis 30 per cent., and it remains nearly at this to theend of the chamber.
(2). Sulphuric Acid , 15 feet from bottom .—At 10feet from the entrance there is no sulphuric acid,and this is the case up to 140 feet, with very littlevariation. The highest is reached at 50 feet, whereit is 23 per cent.; on the whole showing very littleproduction at this height compared to the 3 feetfrom the bottom, where the acid was in markedcontrast. In the sulphurous acid experiment thelargest amount is at the top of the chamber, and thesmallest at the bottom; but in the sulphuric acidexperiment the largest amount is at the bottom, andthe smallest amount at the top.
Nitric Add .—The variations were found not to beso marked as in the above, the differences beingbetween 3 per cent, and 26 per cent. At 100 feetfrom the entrance it was highest, and at 140 feet itrapidly sank to 3 per cent.
II. A. Smith concludes that a chamber should bedivided into two parts, the working portion and thereservoir for the stock of gases; and that if the heightof the chamber was lowered, and at the same timeits length was increased, we should have a bettercondensing surface, as most of the acid appears to beproduced next the already formed acid at the bottom,and he suggests as a good size for a chamber, tohave it about 150 feet long, 25 feet broad, and 12feet high.
The heat at which a chamber is worked is animportant part of the operation of an acid-maker,and it is generally admitted that, to do well in theproduction of acid, the working part of the chambershould never be below about 200° Fahr. Underthat heat little or no production takes place; afair working heat may be considered to be about220° Fahr. This applies especially to the lowerregions of the chamber; but the upper part, nearer
VOL. II.
the roof, is seldom or never so high, and rangesfrom 120° to 150° Fahr. Many of these results,however, as to heat and production, depend verymuch upon the size of the chamber and the wayit is worked; and some manufacturers believe thatsurface as well as space has much to do with therapid and large formation of sulphuric acid. Wardtook out a patent for the use of sheet-glass, whichhe placed in a chamber 200 feet long, 3 feet high,and 3 feet wide, and each sheet was placed about 1inch apart, so that the mixed gases passed betweenthe damp sheets of glass and were rapidly condensed.Steam was introduced at certain points, so as toproduce an acid standing about 135° Twad. (specificgravity, 1-675), which contained a good deal ofnitrous acid, and was all taken to the Gay-Lussac denitrating column, to free it of its nitrous fumes.The patentee claimed for his method a greater makeof acid in a given space, a larger production of acidfrom a given weight of pyrites, a smaller quantity ofnitrate of soda, and the wear and tear of the chamberreduced. This class of chamber was tried on theThames by the late T. Bell, but has not come intogeneral use.
In 1844 a great saving was effected in themanufacture, by the adoption of Gay-Lussac ’sprocess for the recovery of the nitrous compounds,which had hitherto been allowed to escape intothe air and were wasted. This important improve-ment consisted of absorbing the nitrous gases bymeans of strong oil of vitriol. It was intro-duced into England by I)e Couecy; and its adop-tion has lead to a decrease in the consumptionof nitrate of soda, equal to more than one-half ofthe quantity formerly used. The method which isusually adopted in chemical works is as under:—■The whole of the hot sulphurous gases from theburners is made to pass under and over a metalpot inclosed in tight brick work, in which is placeda charge of nitrate of soda and sulphuric acid. Thelengtli of time required to decompose the nitredepends on the weight used; but the pot is usuallyrun off every three or four hours, and a fresh chargeis made to enable the supply of nitrous fumes to thechamber to be continuous. Fig. 4 is a section ofone of the nitre pots now in use:—
Fig. 4.
The sulphate of soda formed from the decomposi-tion of the nitre is in a semi-fluid condition, and isrun off from the pot by means of a plug, P; andafter cooling, is broken up and used in the sodaprocess. The analysis is as under:—
Sulphate of soda,. 81-25
Free sulphuric acid. 17-10
Salts of lime, iron, &c.,. 1-75
Water (uncombined),. 0 ’50
100-60
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