eam
pressures until the resistance became relatively too great. The process
described above is illustrated by the diagram Fig. 1, which is drawn
according to the observations during the experiment.

[Footnote 3: Zeitschrift d. Vereins Deutscher Ingenieur, 1883, p. 730;
1884, p. 69.]

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

The constant rise of both temperatures during the first two hours, which
is an undesirable feature of this experiment, was caused by the quantity
of soda lye being too great in proportion to that of water, and other
experiments have shown that it is also caused by an increased resistance
of the engine, and consequent greater consumption of steam. In the latter
part of the experiment, where the engine worked with expansion, the rise
of the temperature was much less, and by its judicious application,
together with a proper proportion between the quantities of the two
liquids in the engines, which are now in practical use, the rising of the
temperatures has been avoided. The smaller the difference is between the
temperatures of the soda lye and the water the more favorable is the
economical working of the process. It can be attained by an increase of
the heating surface as well as by a sparing consumption of steam,
together with an ample quantity of soda lye, especially if the steam is
made dry by superheating. In the diagrams Figs. 3 and 4, taken from a
passenger engine which does regular service on the railway between
Wurselen and Stolberg, the difference of the two temperatures is
generally less than. 10 deg. Cent. These diagrams contain the
temperatures during the four journeys _a b c d_, which are performed with
only one quantity of soda lye during about twelve hours, and show the
effects of the changing resistances of the engine and of the duration of
the process upon the steam pressure, which, considering the condition of
the gradients, are generally not greater than in an ordinary locomotive
engine. It can especially be seen from these diagrams that an increase of
the resistance is immediately and automatically followed by an increased
production of steam. This is an important advantage of the soda engine
over the coal-burning engine, in consequence of which less skill is
required for the regular production of steam power. The tramway engines
of more recent construction according to Honigmann's system--Figs. 5 and
6--are worked with a closed soda vessel in which a pressure of 1/2 to