TREATMENT OF RAGS 25

The steam pressure varies according to local conditions, such as the boiling
capacity of the mill, the nature of the rags, etc., but it can be taken as estab-
lished that a long boil at a low temperature gives better results than a quick
and drastic boil at very high pressure and temperature. For all ordinary grades
of rags 20 to 25 Ib. to the square inch is sufficient, and recording steam pressure
and temperature meters should be installed, so that the actual pressures and

[Messrs. R. Lord and Sons, Bury
FIG. 5.—SPHERICAL RAG BOILER, HOLDING UP TO SDC TONS; FITTED WITH LARGE MANHOLE TO EMPTY IN ONE OR Two
REVOLUTIONS
temperatures being used can be seen at any time. Thermostats are now avaikble
for controlling the latter.
As soon as the pressure reaches the required level, the steam should be turned
off, and no more allowed in so long as the pressure keeps up. Reducing valves
and safety valves must, of course, always be fitted to prevent dangerous pressures
from being reached. The action of the alkalis on the rags is to remove grease,,
which is always present in rags, and to convert it into soluble soaps, which are
washed out in the washing water. The alkali also removes a great deal of
colouring matter, starch, size and other impurities.