the evaporation of water
in concentrating the soda lye can therefore be directly compared with
that required in an ordinary engine for the production 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