MODERN IRISH PROCESS FOR 3000 LB. CREAM LINEN.
1. Lime: 160 lb. lime.
2. Lime boil : 10 to 12 hours, low pressure, 3 to lb. ; wash 40 minutes in stocks.
3. Sour : hydrochloric acid, 21° Tw., steep 2 to 4 hours ; wash 40 minutes in stocks; " turn bank," and wash 30 minutes in stocks.
4. Leyboil : lat. 200 lb. soda ash and 60 lb. resin, previously boiled and dissolved together in water ; 400 galls. of water ; boil 6 to 7 hours; wash 40 minutes in stocks.
5. Expose in field, 2 to 7 days, according to weather.
6. Chernick : chloride of lime solution Tw., steep 3 to 4 hours; wash 40 minutes in stocks.
7. Sour : sulphuric acid 1° Tw., steep 2 to 3 hours; wash 40 minutes in stocks. , 8. Leyboil, or " scald": 2nd. 400 lb. soda ash, 400 galls. water, boil 4 hours; wash 40 minutes in stocks.
9. Rub witb rubbing machine and good solution of soft-soap.
10. Expose in field, 2 to 4 days.
11. Chemiek : chloride of lime solution r Tw., steep 3 to 4 hours ; wash 40 minutes in stocks.
12. Sour : sulphuric acid 1° Tw., steep 2 to 3 hours ; wash 40 minutes in stocks.
It is possible to bleach some goods without limeing, and, when it can be avoided, they are much softer. What is known as " brown holland " is a 'plain woven linen cloth which has had little or no bleaching, but only a slight boiling in water, or a weak soda-aah solution, with, perhaps, a little souring. It therefore has the natural colour of the linen fibre.
During the limehoil, a portion of the brown colouring matter (pectic acid) is dissolved. Dr. Kolb finds that for every hundred parts so dissolved, 48 parte of lime enter into solution. The same precautions as are mentioned uuder " madder bleach " must be even more rigorously attended to here.
The boiling with alkali removes still more of the pectic acid, also the fatty and greenish matters present. Carbonate of soda seems to dissolve more of the greenish and less of the fatty matter, hence linen yarns boiled with soda ash are somewhat softer than those treated with caustic soda.
After the leyboils, the goods should never be allowed to lie exposed to the air too long before washing, otherwise they are apt to be tendered in places, by the crystallization of carbonate of soda within the fibres, which are cut or burst during the formation of the crystals.
The loss in weight by the boilings with lime, and caustic (or carbonate of) soda varies from 15 to 36 per cent., according to the origin and previous treatment of the yarn. Unbleached yarn boiled with water alone for a week, under a pressure of 75 lb., loses about 18 per cent. In all these cases, the insoluble pectic acid is changed into soluble metapectic acid, which combines with the alkali, driving off the carbonic acid when soda ash is used (Kolb).
After a number of successive hoilings with alkali, the brownish colour of the fibre disappears, and the goods only retain a pale grey shade, which varies in hue according to the process of rettiug employed. In this case, the pectic matters have been thoroughly discharged, and the remainiog grey colouring matter is readily bleached, by steeping in a weak solution of chloride of lime, without injury to the fibre. The brown pectic matters are only bleached with great difficulty, and even then only by using a chemick solution of such a strength that the fibre itself is attacked; hence this agent must never be relied on, in the earlier stages of the process, to remove the brownish colour of the fibre ; and, since scarcely more than 10 per cent. of the pectic matters are ever removed in practice by a single leyboil, it is only by repeated treatments with alkali that the whole of these matters are eliminated.
The great excess of pectic matters prevents the " chemick " from decolorizing the whole of the grey matters at one operation ; hence the necessity for alternating the alkaline boilings with more and more dilute chloride of lime treatments. If the " chemick " is used at too early a stage, the brown colour becomes fixed or " set," and can then only be removed with the greatest difficulty, if at all.