Notes on Resin Boil.—As already stated, the fatty matters remain in the cloth after the grey sour ; but, being in the altered state of fatty acids, they are readily dissolved off, in the boiling with soda ash and resin soap, along with the brown colouring matters and everything else soluble in alkaline liquids. Formerly soap, soda, or potash was used. Soda ash or caustic soda alone is still used by those bleachers whose goods are sent white into the market ; but for calico which is to be printed and dyed, the addition of resin soap is essential. Experiments made on the large as well as on the small scale, to be detailed afterwards, amply prove this. What the peculiar action of the resiu is in this respect is not known. O'Neill states that he has used in its stead a coarse soft-soap made from sunflower oil, and with equal results. The subject is worth further inquiry. The date of the intro duction of resin for bleaching purposes is not definitely fixed ; from all accounts, it seems to have been about 1830. The usual amounts iu vogue at present are : 11- to If lb. of resin, and 4 to 4,1 lb. soda ash (at 58 per cent.) per I00 lb. calico. With low-pressure kiers, steam at 8 to IO lb. pressure, the boiling is continued twelve to fourteen hours ; with Barlow's kiers, about seven to ten hours, according as the pressure of steam used is 50 lb. or 35 lb. per sq. in. With the new injector kier, three to four hours at 45 to 50 lb. pressure of steam is deemed sufficient. Some bleachers boil one to three hours with soda ash alone, both before and after the resin boil, using 1 to 2 lb. soda ash per 100 lb. cloth. The first soda-ash boil, though not absolutely necessary, is advisable, in order to neutralize any traces of acid accidentally left in the eloth through defective washing ; and of course the soda ash liquor should be run into the kier without any previous heating of the goods by blowing steam through, as is the custom with Barlow's kiers, in admitting the resin soap and other liquors. Another plan is simply to run in the weak solution of soda ash till the goods are com pletely covered, and then to run it off again, before blowing steam through and introducing the regular liquor. This is called " sweetening " the goods. If the water of the bleach-house contains any considerable quantity of lime, a slight soda-ash boil, both before and after the resin boil, prevents the deposition of a lime soap on the cloth, and, in •these circumstances, is advisable. The second soda-ash boil, though sometimes omitted, also ensures a complete removal of grease, and especially any particles of resin which might remain. That resin is not unfrequently left in the cloth is proved by its appearance on the scrimp rails, expanders, ezc., in front of the white drying machines, after a large number of pieces have passed over ; hence the necessity of seeing that the resin is well boiled with a sufficiency of soda ash previous to putting it into the kier. Another very good method of making the resin soap is as follows :—the resin cistern is made up with liquor in the following proportions ; 33 gallons water and 33 gallons caustic soda at 70° Tw. are heated to the boil, 220 lb. resin are then added and stirred for a quarter of an hour or more, the boiling is continued for six hours till the resin is completely dissolved. The alkaline liquor is made strong enough to keep the undissolved resin afloat, otherwise the latter collects as a pasty raass at the bottom of the cistern, and is not so readily dissolved. The cistern is, of course, filled up in the proportions given, these only representing the amount required for one boiling of 2,000 lb. cloth, for which there would also be used, along with the resin soap just given, soda-ash liquor equal to 450 lb. dry soda ash.
When the goods have been boiled in soda ash, it is very important not to leave them lying in the kier for any length of time after the liquor has drained away; they should be washed as soon as possible, since they are very liable to get iron stains at this stage, either from the sides of the kier or otherwise. There is no fear of the goods heing tendered during a soda-ash boil, unless, per chance, the ash contains caustic soda, and then, if there is a sufficiency of liquor, it is entirely prevented.
Notes on Chemicking.—It is the bleaching-powder solution which is essentially the whitening and colour-destroying agent, and its application is absolutely necessary, after the removal from the cloth of all fatty and other foreign matters, in order to destroy the slight creamy colour still remaining. Before its use was properly understood, it was often applied previously to the removal of the fatty impurities, and oxidizing these, and forming insoluble lime soaps, it produced stains which withstood even an acid bath. Olive and other oils, if hailed with a sufficient amount of bleaching powder solution, givb a white, solid, wax-like body totally insoluble in boiling caustic alkalies or in strong acids. Dry chlorine ga.s in the dark does not in general decompose dry colouring matter; light, and especially inoisture, are necessary to produce reaction. The bleaching effect of the chemicking takes place principally while the goods are lying saturated with the weak solution of bleaching powder, which is partly decomposed by the carbonic acid of the air, as well as by the cotton fibre itself, The bleaching is completed on the subsequent treatment with acid, the .dis engaged chlorine gas destroying the very last traces of colour. It is advisable never to use the "chemick " so strong that chlorine or hypoehlorous acid gas is evolved in any considerable quan tity in souring, and the best method is to wash the goods between chemicking and souring. Care must be taken to have the bleaching-powder solution perfectly free from undissolved par ticles, otherwise holes in the cloth are sure to result ; neither must it be too strong, too warm, nor too long in contact with the cotton, for the same reason. Goods which have been properly heated with lime, acid, and alkali, should only reqiiire a very weak chemicking to make them of snowy whiteness. Should a stronger treatment be necessary, it is better to give the goods two or even three treatments with weak chemick than to risk a strong solution. It is usual and best to chcmick cold ; with a luke-warm solution, better white is obtained and more quickly, a warm weak bath acting as well as a cold strong one. If the bleaching-powder solution is only a little too strong, the cloth becomes rotten, and, if heated, it would be gradually quite destroyed, since, as Payen has shown, cellulose dissolves in such a solution with evolution of carbonic acid ges even at 50° (122° F.). The usual strength of ehemick liquor is i° to i° Tw. When the pieces bave been running in this liquor for some time, the use of the hydrometer would be misleading, hence a rough and ready, hut tolerably exact method of testing is adopted. The following test solutions are required :— Arsenic Solution.-3i grains arsenious acid are dissolved by boiling in 1 quart caustic soda at 16° Tw., then cooled.
Indigo Indicator Solution.-1 measure extract of indigo of good quality, 24. measures sulphuric acid at 144° Tw., 51 measures water, mixed well and filtered : 200 grain measures of this indicator should require l00 grain measures bleaching liquor at i° Tw. to decolorize it Test Solutions for use.—(a) 2 measures arsenic solution, 71 measures water, 4 measures indigo indicator solution, = 13i measures. (b) measure arsenic solution, Ili measures water, i measure cochineal liquor at 6° Tw., =131 measures. Ube cochineal liquor at 6° Tw. is made up with I measure of a watery solution of cochineal at 12° Tvv. and measure of methylated spirit, this is to prevent the solution from moulding. In testing, about i of the chemick liquor is used to decolorize the cochineal. Either of these test solutions can be used with the same graduated phial, which should be of thick glass and cylindrical, about 8 in. long and 11 in. in diameter. This phial ehould be graduated empirically by a chemist in the laboratory, so that each diviaion shows -6° Tw. of bleaching liquor, thus :— The highest number, 8, is of course marked below.