BLEACHING

is the she rae 3 materials by chemical treatment. e materials may be cotton, linen, wool, silk, straw, etc., and the b. may be by oxidation or reduction. Oxidizing b. agents are: b. powder prepared by saturating slaked lime with chlorine gas); eau de Javelle (pota ium hypochlorite, KOCl); sodium hypochlorite, NaOCl (obtained by pa ing chlorine into sodium hydroxide solution: by electrolysis of sodium chloride soluOOCl+H:;0); air and ozone; sodium peroxide, Na20:;; hydrogen peroxide, H.0;; pota ium permanganate, KMnO,, and dichromate, K:Cr20;. The most important of these agents is b. powder, from which chlorine is liberated by dilute acid, thus: CaCCl.+2HCl=CaCl.+H:0+Cls. Dry chlorine will not bleach, and the action of moist chlorine is attributed to the liberation of nascent oxygen from water, thus: Cl.+H.0= 2HCI1+0. So bleaching is due to oxidation.; Reducing b. agents are: sulphur dioxide, SO.; sulphurous acid, H.SO;, and sulphites, (e.g.) sodium ‘meta bisulphite,’ NaS.0;; hydrosulphites (or true hyposulphites), e.g. sodium hydrosulphite, Na2S.0.+2H.,0. B. by reduction is probably due to the addition of hydrogen to the coloring matter, thus: $0.+2H.0 =H.80.+2H, and is not so permanent as b. by oxidation, because oe craeeleaam by the air gradually takes place.