26 MODERN PAPER-MAKING
"When lime is used instead of caustic soda or soda ash, there is the risk of
the formation of insoluble compounds, and the rags are often hardened; never-
theless, in some mills where the washing water is very soft, the addition of lime
seems to be absolutely imperative, otherwise it is impossible to get rid of all
the grease, and it is found coating the sides of the breaker. In other mills
where the water is very hard the use of caustic soda together with soda ash
gives the best results in "practice.
Below is a table of the amounts of caustic soda and alkali used on various
qualities of rags where the pressure employed was 25 Ib. per square inch. The
amounts were arrived at after long and careful trials, but of course they were
not always strictly adhered to; the quality of the rags in each boil was always
taken into account, and slight alterations were made both in the quantities of
alkali and the number of hours of boiling. No more water than is necessary to
prevent the rags being 'burned' should be used, as the more concentrated
the alkali solution the more economical will the boiling be.
BOOING DETAILS FOB A I-TON BOILER DEALING WITH RAGS FOR THE HIGHEST GRADES OF WRITING PAPERS •
(Pressure 25 Ib. per square inch. Hot water washed)
Caustic Soda Soda Ash
Hours of Boil (Lb.) (Li.)
Fines, ordinary............ 4-5 25 28
Muslins, clean............ 4 — 28
„ soiled ., .......... 5 — 56
New unbleached calico ('greys') ...... 5 25 —
New white cuttings (second quality) .. ,. 3-4 — 12
New lace cuttings .......... 4 — 12
Seconds, dirty white (outshots) ...... 6 50 28
1 „ light .......... 8 100 56
„ low quality ........ 8 125 56
Old light prints, good.......... 7 100 28
„ low.......... 8 125 56
Cotton canvas............ 10 125 56
Linen canvas............ 10 250-300 112
French linens........ ,. .. 8 250 112
Cords, light............ 10 125 56
Ticking, linings, etc........... 10 150 56
Cotton healds .......... 6 50 —
White cotton tents.......... 7 100 28
Hlter-dotks *. ., ........ 8 100-200 56-112
Old white linens .,....*... 6 75 56
When the boil is complete the boiler is blown off, and the dirty water con-
taining the dissolved grease, etc., is run away to the sewer or other convenient
place, unless the soda is to be recovered. The boiler is then filled up with hot