The apparatus consists of an electric resistance furnace containing coils of nickel wire, a small (interchangeable) multi-tubular boiler, and a steam-jet apparatus for reducing the air pressure at the exit end, so as to cause a flow of air through the boiler. A surface condenser was attached to the boiler’s steam outlet, the condensed steam being weighed as a check on the feed-water measurements. A number of thermometers and thermo-couples were used to obtain atmospheric-air temperature, temperatures of the air entering and leaving the boilers, and feed-water temperature. The apparatus is now being reconstructed with appliances for measuring the quantity of air entering the furnace, and an automatic electric-furnace temperature regulator. [Illustration: PLATE XIX. Fig. 1.--Gas Producer, Economizer, and Wet Scrubber. Fig. 2.--Producer Gas: Dry Scrubber and Gas Holder.] Three sizes of boiler have been tested thus far, the dimensions being as given in Table 4. Each of the three boilers was tested at several temperatures of entering air, up to 1,500° Fahr., about ten tests being made at each temperature. It is also the intention to run, on these three boilers, about eight tests at temperatures of 1,800°, 2,100° and 2,400° Fahr., respectively. A bulletin on the work already done, together with much incidental matter, is in course of preparation.[18] TABLE 4.--Dimensions of Boilers Nos. 1, 2, and 3. ------------------------------------+--------+--------+-------- Items. | Boiler | Boiler | Boiler | No. 1. | No. 2. | No. 3. ------------------------------------+--------+--------+-------- Distance, outside to outside of | | | boiler heads, in inches | 8.28 | 8.28 | 16.125 Actual outside diameter of flues, | 0.252 | 0.313 | 0.252 in inches | | | Actual inside diameter of flues, | 0.175 | 0.230 | 0.175 in inches | | | Number of flues (tubes) | 10 | 10 | 10 ------------------------------------+--------+--------+-------- The work on the first three boilers is only a beginning; preparations are being made to test eight more multi-tubular boilers of various lengths and tube diameters, under similar conditions. Because of the experience already obtained, it will be necessary to make only eight tests at each initial air temperature. When the work on multi-tubular boilers is completed, water-tube boilers will be taken up, for which a fairly complete outline has been prepared. This second or water-tube portion of the investigation is really of the greater scientific and commercial interest, but the multi-tubular boilers were investigated first because the mathematical treatment is much simpler.