Formerly this delivery apparatus consisted of a simple tumbling trough, such, as we have already described. The quantity of acid required is so small, however, that the intervals between the discharges from the trough were found to be too long, and too much acid was delivered at a time. The apparatus also easily becomes disarranged. For these reasons it is now discontinued in most works.
Another plan, shown in Fig. 50, consists of four rows each of four drip pipes, equidistant from each other and fastened securely into the cover of the tower. These pipes are furnished at top with a funnel, and underneath are bent up and down so that the suspended liquid cuts off com munication with the outside air. The acid is conveyed from the cistern T through the pipe o to the drip tubes, the pipe o being divided into two branches, each passing between two rows of the drip tubes and provided with branches and taps, ao that each drip tube is supplied with acid from a special tap. Thus the supply of acid depends upon the adjuatmeut of aixteen taps. It is, however, very difficult so to regulate each tap that the amount of acid received by each drip tube is exactly correct. The tubes also are very liable to become choked.
The method now in common uae,.alike in this country and on the Continent, is an adaptation of the principle of the turbine. The top of the tower is divided into low-walled compartmenta, each furnished at bottom with a luted exit pipe. Two pipes deacend from a email hopper and are bent round in such a way that the acid flowing from them canoes them and the hopper to revolve. The acid falls ou fireclay tiles inside the tower and then splashes over the coke.
Instead of the tower packed with coke in many Continental works, another arrangement is adopted, shown in plan and elevation in Figs. 52 and 53. It consists of thirty to forty stoneware jars k, about 3 ft. high. They are connected with pipes of the same material placed in the necks c and plastered with putty. In order that the gases may be acted upon as much as possible, they are led through the jars, where they come into contact with acid of about 150° Tw., with which the jars are one-third filled. After giving up their nitrogen compounds to the sulphuric acid they escape at d into either the draught pipe or the chimney, as the case may be.
For convenience in filling the jars, funnels h can be inserted into their necks f, descending almost to the bottom of the jars and thus preventing the escape of gas by the acid lying there. The acid is drawn off at the taps g. In order that the acid may absorb as much nitrous gas as possible, it is allowed to remain twenty-four hours on each row of jars. The first row is emptied daily, and refilled with the acid taken from the second row, the second row ia supplied from the third and into the third fresh acid ia put. It is convenient to put the second row at a higher level than the first, and the third higher than the second, so that the acid may flow from one row to another without trouble. The jars of the highest row are filled from a cistern standing above them.
A modification of this plan is comprised of large saucers a, Fig. 54, covered with belle b and joined together by pipes c. This arrangement possesses the advantage that each portion of the apparatus is lighter and cheaper, and that the acid can run from oue to another, terrace-like, in a direction opposite to that of the gases.
In order to procure for further use the nitrous acid thus entrapped, it must be liberated from the aulphuric acid. Formerly this was dove by letting tho mixed acids flow into the largest chamber near the gases entrance. The operation ia now more effectually performed iu a small chamber, as shown in Fig. 55 (B). The mixed acids are first placed in the cistern F and run thence tluough the tap c, which regulates the outflow, and then through the funnel-topped bent tube d into the chamber, which is furnished with horizontal leaden shelves over which the acid flows. These shelves aro burnt to the walls of the cham ber on three sides, and on the fourth, where tile acid flows over, they are furnished with low rims about 4 in. high to detain the acid. The gases rush immediately out of the sulphur burner into the small chamber through the pipe C a little above the bot tom, near which at b the necessary steam is introduced, and escape from the top along with the nitrous acid fumes liberated from the nitro-sulphurio acid through the pipe E into the large chamber, whilst the deni trated acid flows into the baain of the chamber by the pipe c.