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28.

3d. Elbow [[underline]] E [[/underline]] cut at [[underline]] E [[/underline]] [[subscript]] o [[/subscript]], and tank half filled with 1/2-inch square-mesh wire fencing. Two separate devices constructed of this wire fencing were used one above the other. The gas first passed through an Archimedes spiral, [[underline]] J [[/underline]], of 2-foot fencing, comprising eight turns, held apart by iron wires bound into the fencing. This construction allowed most of the gas to penetrate the spiral to a considerable distance before being disturbed; and, of course, eliminated regular reflection. The second device, [[underline]] J' [[/underline]], placed under the first, consisted of a number of 12-inch circular disks of the same fencing, bound to two quarter-inch iron rods, [[underline]] [[strikethrough]] P [[/strikethrough]] ^[[Q]] [[/underline]], by iron wires.  These disks were spaced one inch apart. The three upper disks were single disks, the next lower two were double, with the strands extending in different directions, the next two were triple, and the lowest disk of all, two inches from the bottom of the tank, was composed of six individual disks. This lower device necessarily offered large resistance to the passage of the gas; yet strong rebounding from any part of it was prevented by the spiral just described. With this third arrangement, small rebound was to be expected; which also was borne out in practice. 

This tank was exhausted by ^[[way of]] a stop cock at its lower end, [[underline]] S [[/underline]]; and air was also admitted through this same stop cock.

The circular tank, Fig. 19, was 10 feet high and weighed about 200 lbs. It consisted of a straight length of 3-inch pipe, carefully fitted, and welded antogeneously, to a four-foot, 3-inch, U-pipe. The straight pipe entered the U-pipe on the inner side of the latter, and at as sharp an angle as possible. Another similar U-pipe, was bolted to the first by flanges, with 1/16-inch sheet-rubber packing between.