The Partington Boiler is spherical ; the lead is applied in spherical limes, clamped to the iron, and burned to each other. The theory is, that it is an easy matter to replace an injured section, and thus to keep the lining intact at comparatively little cost.
The Ritter-Kellner Digester, about 10 X 28 ft., is built up of cylindrical sections, 4 ft. wide, a few incites apart, and fastened by heavy exterior bands. The object of this construction is to provide the means for attaching the lead lining peculiar to this process. The spaces be tween these sections form annular dovetail mortises, which are filled with an alloy of lead and :antimony, and at the ends of a dhnlleter meet similar vertical tenons, to which they are attached. The hning, is burned fast. to this semi-cylindrical frame. Dere, again, under the irresistible force of expansion, these great sheets of lead. roughly speaking 10 X 4 ft., must theoretically, if the tacking holds, "pucker lip," and again be forced back against the shell limier contraction and pressure.
The Graham Digester. 7l X 2i ft., is made of sheets of boiler-plate, to which the lead lining is soldered before bending and assembling. The method of doing this is ingenions and simple. The sheet is cleansed and smoothed by a radially traveling emery-wheel: it is then firmly tixed for half its surface over a gas-jet heater. The rectangular frame that holds it down is packed with fire-proof packing where it rests upon the plate, thus actually forming a water-tight vessel, of which the iron to be leaded is the bottom. The plate is copiously doused with a solution of chloride of zinc, and, when heated to the proper degree, molten lead in suf ficient quantity is poured upon it. Although the promoters of this process do not so call it, it is, nevertheless, soldering. which is authoritatively defined to be the process of uniting two pieces of the same or of different metals by tile interposition of a metal or alloy, which, by fusion, combines with each." ilitseherlich Digester is lined with an acid-proof brick of special de sign, laid in Portland cement. Apparently a startling innovation, reflection proves that this method follows out the direct line of modern progress. The manufactnre of that almost in dispensable article, sulphuric acid, has in pomparatively late years been greatly improved and facilitated by the introduction of the Gay-Lussac and Glover towers, edifices lined, not with lead, but with acid-proof tiles or brick.
Unlined Digesters.—The Digester is a stationary. upright cylinder, 7 ft. in diameter by 22 ft. 'height, and is made in sectional castings of deoxidized bronze, with planed flanges, which are bolted together and lead-jointed in assembling. This alloy the designer assumes is
sufficiently acid-proof for the purpose, without the protection of other resistant lining. It is acknowledged that the deoxidized bronze is acted upon by the acid solution, and observation confirms this conclusion; bat it is claimed that this erosion is so slight that the longevity of the digester is not threatened thereby.
Acid Process.—The manufaeture of the bisulphite solution may be classified under three heads: the vacuum process, the modified tower process, the tower process. The vacumn sys tem is used in connection with the Partington, the Schenk. and the Graham processes. It requires large exhaust-pumps, a series of tanks arranged vertically in echelon, a lime-mixer, etc., and undoubtedly yields with certainty the high solution required. It can be used for all the processes. The modified tower system, in use with the hitter-Kellner process at Corn wall, is a sort of cross between the 3litscherlich tower and vacuum method. The solution is pumped by a battery of pumps into a series of low towers under cover, filled with limestone. The 31itseherlich tower process is in a measure automatic, and is certainly the most economi cal. The sulphurous-acid gas is drawn up the high towers, filled with limestone, by atmos pheric draft, and therein meets water trickling, through the filling. Its main distulvantage is the assurance of proper draft. The consumption of sulphur varies from 200 lbs. per ton of fiber in the Mitscherlich up to nearly 600 lbs. in the others. In none of the others is it less than 350 to 400 ills, Jfechanical Preparation of the Wood.—All the processes, except the Mitscherlich, use chips. In this latter, disks cut out from the log. 11 in. deep, are used. Dr. Mitscherlich claims that these disks afford a stronger fiber, and that more bulk can be put into the digester than if loosely piled chips were used.
A recent form of digester of English manufacture is repre sented in Fig.]. It is made of Sieeileus-Mar thi mild steel plates, ?; in. thick and 12 ft. in diameter inside. The rivet-holes on the in side are countersunk, to present a level sur face to the lead lining, w h ich is patented. The lining is made in large sheets, and is held against the steel shell by means of a series of clamps fast ened front the outside. The digester is filled through the man-hole, which is 2 ft. in diam eter, from a high lev el, with timber and sulphite liquor. and steam passes in at a pressure of 70 lbs. through the trunnions, while the digester is slowly re volved by means of the bevel and worm gearing, as shown in the engraving.
Disintegrator : see Clay-Working Machinery.