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 11/2 atmospheres is gradually developed during the process.  While the counter pressure thus produced offers only a slight disadvantage, being at an average only 1/2 atmosphere, the absorbing power of the soda lye is materially increased, as shown by the following table, and it is, therefore, possible to work with higher pressures than with an open soda vessel.  Besides this great advantage, it is also of importance that the pressure in the steam boiler can be kept at a more uniform height.

[Illustration:  FIG. 3.]

[Illustration:  FIG. 4.]

TABLE.—­100_kilogs.  Soda Lye containing 20 parts Water with a corresponding boiling point of 220 deg.  Cent. absorb Steam as follows_: 

+----------------------------------+--------------+----

-----------+
|Final pressure in condenser.      |              |               |
+----------------------------------+Pressure in   |Corresponding  |
|  0    | 1/2 atm. | 1 atm. | 11/2 atm.|steam boiler. | temperature.  |
+----------------------------------+--------------+---------

------+
|80 kil.|125 kil.|200 kil.|350 kil.|  2 atm.      | 136.0 deg.  C. |
|65  "  | 88  "  |130  "  |190  "  |  3  "        | 143.0   "     |
|51  "  | 70  "  | 98  "  |125  "  |  4  "        | 153.3   "     |
|41  "  | 58  "  | 80  "  |100  "  |  5  "        | 160.0   "     |
|34  "  | 48  "  | 66  "  | 80  "  |  6  "        | 166.5   "     |
|27  "  | 40  "  | 55  "  | 70  "  |  7  "        | 172.1   "     |
|221/2 "  | 33  "  | 47  "  | 60  "  |  8  "        | 177.4   "     |
|19  "  | 28  "  | 41  "  | 52  "  |  9  "        | 182.0   "     |
|16  "  | 24  "  | 35  "  | 46  "  | 10  "        | 186.0   "     |
|12  "  | 18  "  | 28  "  | 35  "  | 12  "        | 193.7   "     |
| 9  "  | 14  "  | 22  "  | 33  "  | 15  "        | 200.0   "     |
| 2  "  |  8  "  | 12  "  | 21  "  | 20  "        | 215.0   "     |
+-------+--------+--------+--------+--------------+---------

------+

Not the least important part of the process with regard to its economy is the boiling down of the soda lye in order to bring it back to the degree of concentration which is required at the beginning of the process.  This is done in fixed boilers at a station from which the engines start on their daily service, and to which they return for the purpose of being refilled with concentrated soda lye.  It is clear that a closed soda vessel has produced as much steam when the process is over as it has absorbed, and the quantity of coal required for the evaporation of water in concentrating the soda lye can therefore be directly compared with that required in an ordinary engine for the production