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