BLEACHING.
135
stitution. This is, however, probably not the part which oxygen plays, nor is it the onlyprinciple in the atmosphere which exercises a bleaching influence. Neither is the actionof chlorine such as has been commonly represented in our chemical systems.
But if authors offer us only vague hypotheses concerning the three principal agents,light, oxygen, chlorine, they afford no information whatever concerning the phenomenadue to greasy spots so frequently found upon cotton cloth, and so very troublesome tothe bleacher. It has indeed been sometimes said in bleach-works, that fatty sub-stances are no longer soluble in alkalis, when they are combined with oxygen. TheVei 7 reverse of this statement is probably nearer the truth.
The object of bleaching is to separate from the textile fibre, by suitable operations, allthe substances which mask its intrinsic whiteness: or which, in the course of ulteriordyeing operations, may produce injurious effects. In this latter respect, cotton deservesespecial consideration. This substance is covered with a resinous matter, which obstructstis absorption of moisture, and with a yellow coloring matter in very small quantity,®ften so inconsiderable in some cottons, that it would be unnecessary to bleach them,before submitting them to the dyer, were it not that the manipulations which theyundergo introduce certain impurities which are more or less injurious, and must beremoved. It is in fact a circumstance well known in the factories, that unbleachedcottons may be dyed any dark color, provided they are deprived of that matter whichb'skes them difficult to moisten. The substances present in cotton goods are thefollowing:_
L The resinous matter natural to the cotton filaments.
2. The proper coloring matter of this vegetable.
” The paste of the weaver.
;• A fat matter.
A cupreous soap.
b- A calcareous soap.
A The filth of the hands.
• Iron, and some earthy substances.
me ’ fitter which prevents the moistening of cotton wool may be separated byin ns . alcohol, which, when evaporated, leaves thin yellowish scales, soluble in alkalis.Pro C1< * S ’ an< * even a lar S e Quantity of boiling water. For a long time the bleachingVar ^ es ® commenced with the removal of this resinous stuff, by passing the cloth or the
2 f .p 0,J k r b an alkaline ley. This was called scouring ; it is now nearly laid aside.
°n th ^ eo, °™S matter of cotton seems to be superficial, and to have no influencestrip 6 ? tren gth °f the fibres; for the yarn is found to be as strong after it has beencolor’ ^ caustic soda of its resinous and coloring matters, as it was before. Theca li c In S matter is slightly soluble in water, and perfectly in alkaline leys. When grayit Ir| -b ^ boiled in lime-water, it comes out with a tint darker than it had before; whenceThis j su P_posed that the coloring matter was not dissolved out, even in part.We s|’, |? WeVer > is not the case; for if we filter the liquor, and neutralize it with an acid,matter 1 * P^ rc eive light flocks, formed of the resinous substance, united with the coloringPosses" eo ' or °f the cloth is to be ascribed solely to the property which lime
teni»;-- es °*" browning certain vegetable colors. This action is here exercised upon the
Ttm W \ colorofth ® cloth -
vtVeldown as a principle, that the coloring matter is not directly solublethe joint a • ^ Ut ** becomes so only after having been for some time exposed to
change d act ! on °f air and light, or after having been in-contact with chlorine. Whatupon pieo 6S ** thereby experience, which gives it this solubility ? Experiments madechlorine T °*" c ' ot ' 1 Placed in humid oxygen, in dry oxygen, in moist chlorine, and in dryex Periment eni * to show that hydrogen is abstracted by the atmosphere; for in lhc.seIn a i] s Proofs of dis-hydrogenation appeared, and of the production of carbonic acid,hydrogen 0 f bleaching by chlorine, this principle combines immediately with then ated. pj n( j ‘he coloring matter, and forms muriatic acid, while the carbon is elimi-P r °cess is Ql Potcaly water has an influence upon this phenomenon, since the bleaching®ct here onlv 1 ™ 6 !' v t.th the humid chlorine than with the dry; but this liquid seems tos hould also J ?t e . nically, in condensing the particles of the gas into a solution. We
3. Xhe weay 6 ’"a* acc . ount the great affinity of muriatic acid for water.
t° sour befo re < n, S aress t n S is composed of farinaceous matters, which are usually allowedVe J7 soluble in lime ^ em Pl°y e d- It ma y contain glue, starch, gluten; which last is
J? ore pliant b^rnWK- 8 * 1 '* - ets the hand-weaver occasionally renders his warp-threadsI 1 ? cloth which h some cheap kind of grease upon them. Hence it happens, thattnbibe water m the ' >een completely freed from this fatty matter will not readilyr dunging^ these area erent bleaching operations ; and hence, in the subsequent dyeing' ° nes ) strongly attract S ^i SP ° tS ’ u ? ( I er Peculiar circumstances, somewhat like lithographicte aluminous and iron mordants, as well as the dye-stuffs, and