bleaching, straw - Bleaching, Straw bleaching, straw - On a small scale, with such an article as a straw hat, a bonnet, a basket, etc., the following method may be followed:
The straw, having been well washed with weak soda lye, is rinsed in plenty of clean water lightly shaken, etc.; remove superfluous moisture, and place, supported on a stick, under a large glazed earthenware pan (turned upside down). A very small pipkin, capable of holding about ½ pint is now placed on the fire, and about ½ oz. of roll brimstone placed in it. When the brimstone is all melted, a light is applied to it, so as to cause it to catch fire. The pipkin with the inflamed sulphur, is now placed under the glazed pan in such a position as not to scorch the article to be bleached. The spaces between the pan and the table or floor on which it rests, must be carefully closed with damp cloths placed around to prevent the escape of the sulphurous acid gas produced by the combustion of the sulphur. In about 2 hours the pan may be removed, when the straw will be found nicely bleached. N. B. - This operation had better be performed out of doors, as the sulphurous acid gas which is set free on lifting the pan, is extremely irritating to the chest and throat.
Or the articles, having been washed as before, may be placed for an hour in weak chloride of lime water, and then hung out on a line to ' dry slowly. The chloride of lime water should be made by mixing 1 part (by weight) of chloride of lime with 20 of water, agitating the mixture with a stick, until all the particles of chloride of lime are thoroughly broken up allowing the mixture to settle, and pouring off the clear portion from the dregs for use.
In Tuscany, where a considerable amount of straw is bleached, the straw is selected while the wheat is bearded, and the grains still in a soft milky state. In order to ensure the requisite fineness, the corn is sown very thickly, so that the straws are in a dwindled condition. The straws are cut, spread out for 2 or 3 days to dry out the sap, tied up in bundles, and stacked to allow all moisture to dry off. They are then again spread out exposed to the dew and atmosphere, turned over several times, and watered with clean water. After this, the lower joints are cut off, the chosen portions exposed to the action of steam in a steam vat, which further decolorises them, and lastly bleached by exposing to sulphurous acid vapours in closed chambers.
In this country, the straw is prepared by acting upon ordinary materials; first, with a solution of caustic soda, boiling, by which a considerable portion of the organic matter and natural varnish is disintegrated; after this it is washed well to remove all the material which the alkali dissolves, and then exposed to the action of sulphurous acid or chlorine in closed vessels.
Kurrer states that straw may be economically whitened by being steeped repeatedly in boiling water and very weak alkali, and, after all the soluble matters are in this way removed, by treating alternately with very dilute solutions of chloride of lime and sulphurous acid vapour, until decoloration has been effected. This method, though tedious, is said to be very effectual for divesting the straw of its natural varnish, which renders it very brittle.
About 9 oz. of permanganate of potash are dissolved in 1 gal. of warm water. This is done in an earthenware vessel, and cold water is then added until the liquid takes a dark red colour. The straw is left for about 6 hours in a tepid and weak solution of soda crystals. It is then washed carefully and introduced into the permanganate solution, in which it is continually agitated. As soon as it has taken a light brown colour, it is. dipped in cold water, then in a bath of | bisulphite of soda, strong enough to be smelled. In this bath the straw is left for 15 minutes, and when taken out it is perfectly white.
Soak the goods in caustic soda, and afterwards use chloride of lime, or Javelle water (chloride of potash). The excess of chlorine is afterwards removed by hyposulphite of soda (antichlor).