By the improved method of previously treating the goods with lime or alkalies, little chloride of lime is required. Indeed, it is said that where 300 lbs. were formerly employed, 30 to 40 lbs. only are now used. At the same time it is right to mention, that though a solution at 1⁄2° Twaddle is usually regarded as the best and safest strength, yet in some bleach works, particularly for inferior and less tender goods, this is greatly increased, even up to 5°, the period of immersion being proportionately reduced, as it is not safe to expose the goods long to the action of such powerful solutions. With the higher strengths they are passed rapidly through the liquid with the calender, sufficient time only being allowed to soak them thoroughly; then immediately through the acid or souring, followed by washing as before.
In Scotland and Ireland the washing is generally performed by wash-stocks; whilst in Lancashire, dash-wheels, or washing machines with squeezers, are almost always used for the purpose.
Cotton loses about 1-20th of its weight by bleaching.
II. Bleaching of Linen:—Linen may be bleached in a similar way to ‘cotton,’ but the process is much more troublesome and tedious, owing to its greater affinity for the colouring matter existing in it in the raw state. Under the old system, several alternate buckings with pearlash or potash and lengthened exposure on the field, with one or two sourings, and a final scrubbing with a strong lather of soft soap, constituted the chief details of the process. In this way a high degree of whiteness, though not an absolutely pure or snow white, was ultimately produced. Grass-bleaching or crofting is still extensively used for linen; but it is more generally employed only for a limited time, and in combination with a modification of the system at present almost universally adopted for cotton goods; whilst, in some cases, crofting is omitted altogether, and the bleaching conducted wholly by the latter process. The following Tables exhibit the outlines of the new system as at present practised in Ireland and Scotland:—
a. For plain sheetings:—
1. They are bucked for 12 or 15 hours in a lye made with about 1 lb. of pearlash (or soda-ash) to every 56 lbs. of cloth, and washed.
2. Crofted for about 2 days.
3. Bucked in milk of lime.
4. Turned, and the bucking continued, some fresh lime and water being added; and washed.
5. Soured in dilute sulphuric acid at 2° Twaddle.