of an equal quantity of steam.  The boiling down of the soda lye requires, according to its degree of concentration, more coal than the evaporation of water does under equal circumstances, and disregarding certain advantages which the new engine offers in the economy of the use of steam, a greater consumption of coal must be expected.  But even at the small installation for the Aix la Chapelle-Burtscheid tramway with only two boilers of four square meters heating surface each, made of cast iron 20 mm. thick, 1 kilog. of coal converts 6 kilogs. of water contained in the soda lye into steam, while in an ordinary locomotive engine of most modern construction the effect produced is not greater than 1 in 10.  There can be no doubt that better results could be obtained if the installation were larger, the construction of the boilers more scientific, and their material copper instead of cast iron; but even without such improvements the cost of boiling down the soda lye might be greatly lessened by the use of cheaper fuel than that which is used in locomotive engines, and by the saving in stokers’ wages, since stokers would not be required to accompany the engines.

[Illustration:  FIG. 5]

[Illustration:  FIG. 6]

Apart from these considerations, the Honigmann engines have the great advantage that neither smoke nor steam is ejected from them, and that they work noiselessly.  The cost of the caustic soda does not form an important item in the economy of the process, as no decrease of the original quantities had been ascertained after a service of four months duration.  Besides the passenger engine already referred to, which was tested by Herr Heusinger von Waldegg[4] in March, 1884, and which since then does regular service on the Stolberg-Wurselen Railway, there are on the Aix la Chapelle-Julich railway two engines of 45,000 kilogs. weight in regular use, which are intended for the service on the St. Gothard Railway.  Their construction is illustrated in Figs. 7 and 9, and other data are given in a report by the chief engineer of the Aix la Chapelle-Julich Railway, Herr Pulzner, which runs as follows: 

Wurselen, Dec. 23, 1884.

[Footnote 4:  Z.d.V.D.I., 1884, p. 978]

[Illustration:  DIAGRAMS FOR THE CALCULATION OF STRESSES IN BOWSTRING GIRDERS.]

A trial trip was arranged on the line Haaren-Wurselen, the hardest section of the Aix la Chapelle-Julich Railway.  This section has a gradient of 1 in 65 on a length of 4 kilos; and two curves of 250 and 300 meters radius and 667 meters length.  The goods train consisted of twenty-two goods wagons, sixteen of which were empty and six loaded.  The total weight of the wagons was 191,720 kilogs., and this train was drawn by the soda engine with ease and within the regulation time, while the steam pressure was almost constant, viz., five atmospheres.  The greatest load admissible for the coal burning engines of 45,000 kilogs. weight on the same section is 180,000 kilogs.