Rags on the Continent are boiled with lime and soda-ash in a very satisfactory and economical manner, as follows: - No. 1 Stuff.
Lime . . .216 1b Soda-ash (48 %) . 114 „ for 4000 lb. rags, boiled for 12 hours with 30 lb. steam pressure in a boiler revolving horizontally.
Nos. 3 and 5 Stuffs.
Lime .... 3241b. Soda-ash (48 %) . 152 „ boiled as No. I.
for 4000 lb. rags,
No. 4 Stuff.
Lime .... 378 lb. Soda-ash (48 %) . 190 „ boiled as No. 1.
for 4800 lb. rags,
Lime .... 648 lb. Soda-ash (48 °%) . 456 „ for 4000 lb. rope, boiled for 24 hours as No. 1.
Milk of lime is prepared and strained in the following manner:- Construct a wooden box 15 ft. long, 5 ft. wide, and 4 ft. deep, divided into 3 compartments, with false bottoms, perforated with f-in. holes to retain small stones and sand. In the first compartment the lime is slaked and reduced to a powder; it is then put over into the second, and converted into milk of lime. In the partition between the second and third compartments is a movable sluice, allowing the milk to flow into the third division in regulated quantities. In the third compartment is fitted a revolving drum, like the ordinary drum washer of a half-stuff engine. The milk of lime flowing through the sluice is strained by the revolving drum, on the same principle as that by which the water is lifted from a breaking-engine, and discharged through a pipe direct into the rag boilers. If the lime requires extra straining, a fine wire strainer can be put over the mouth of the pipe leading to the boiler. The compartments are furnished with waste pipes, which, with a liberal supply of water, carry off impurities and what the drum has rejected.
This system is satisfactory and cleanly.
The preparation of soda-ash is conducted in different ways. Some introduce it into the newly-slaked lime during the heat generated by the slaking; others put the soda-ash direct into the boiler. The latter should never be done; nothing should go into the boiler without straining. The best method is to dissolve the soda-ash separately, and strain through a fine wire strainer into the boiler.
Boiling with lime alone is much better and safer for fine-textured materials. The rags turn out better, and it is more economical. The quantities of caustic soda per cwt. of the various qualities of rags are as follows: -
S.P.F.F.F. is boiled with lime alone, then washed in the boiler, and again boiled with 2 per cent, of soda ash.
S.P.F.F. is boiled with 12 lb. of caustic soda (70 %) per cwt.; S.P.F., 14 lb.; fines, 7 lb.; seconds, 6 lb.; L.F.X., 20 lb.; C.L.F.X., 27 lb.; C.C.L.F.X., 30 lb.; F.F., 15 lb.; all boiled with steam at a pressure of 20 to 25 lb. for 10 hours in stationary boilers without vomit, and in boilers revolving horizontally.
When esparto is insufficiently boiled, and a repetition of the operation is necessary, great waste of soda is caused, and the material does not turn out satisfactorily. The smallest quantity of caustic soda necessary to boil it properly should be ascertained, and that quantity continued until the parcel is finished. The undernoted quantities of caustic soda (70 per cent.) should boil the various espartos in a satisfactory manner: -
Fine Spanish esparto,
Medium „ „
Fine Oran „
Medium Oran „
Fine Susa „
all boiled for 10 hours in stationary vomiting boilers with 10 lb. steam pressure, taking care that the esparto is sufficiently boiled before the liquor is run off.