OXYMURIATIC ACID (See CHEMISTRY-Index in this Suppl.), is the principal agent in the new process of bleaching (see BLEACHING, Suppl.); but, till very lately, at least, if not even at present, the bleachers were in the practice of adding some alkali to the acid, notwithstanding the strong objections which M. Berthollet made to that addition, and notwithstanding the proofs urged by Mr Rupp, that it increases the expense of bleaching about 40 per cent. The chief reason for persisting in a practice to which such objections were urged was, that the addition of the alkali deprives
the liquor of its suffocating effects without destroying its bleaching powers. Mr Rupp, however, has contrived the following apparatus, in which may be safely used the pure oxy muriatic acid simply dissolved in water, which is at once its cheapest and best vehicle.
Figure 1. (Plate XLI.) is a section of the apparatus. It consists of an oblong deal cistern ABCD, made water-tight. A rib EE of ash or beech wood is firmly fixed to the middle of the bottom CD, being mortified into the ends of the cistern. This rib is provided with holes at FF, in which two perpendicular axes are to turn. The lid AB has a rim GG, which sinks and fits into the cistern. Two tubes HH are fixed into the lid, their centres being perpendicularly over the centres of the sockets FF when the lid is upon the cistern. At I, is a tube by which the liquor is introduced into the apparatus. As it is necessary that the space within the rim GG be air-tight, its joints to the lid, and the joints of the tubes, must be very close; and, if necessary, secured with pitch. Two perpendicular axes KL, made of ash or beech wood, pass thro' the tubes HH, and rest in the sockets FF. A piece of strong canvas M is sewed very tight round the axis K, one end of it projecting from the axis. The other axis is provided with a similar piece of canvas. N are pieces of cloth rolled upon the axis L. Two plain pulleys OO are fixed to the axes, in order to prevent the cloth from slipping down. The shafts are turned by a moveable handle P. Q is a moveable pulley, round which passes the cord R. This cord, which is fastened on the opposite side of the lid (see fig. 2.), and passes over the small pulley S, produces friction by means of the weight T. By the spigot and fauſſet V, the liquor is let off when exhausted.
The dimensions of this apparatus are calculated for the purpose of bleaching twelve or fifteen pieces of calicoes, or any other stuffs of equal breadth and substance. When the goods are ready for bleaching, the axis L is placed on a frame in an horizontal position, and one of the pieces N being fastened to the canvas M by means of wooden skewers, in the manner represented in fig. 1. it is rolled upon the axis by turning it with the handle P. This operation must be performed by two persons; the one turning the axis and the other directing the piece, which must be rolled on very tight and very even. When the first piece is on the axis, the next piece is fastened to the end of it by skewers, and wound on in the same manner as the first. The same method is pursued till all the pieces are wound upon the axis. The end of the last piece is then fastened to the canvas of the axis K. Both axes are afterwards placed into the cistern, with their ends in the sockets FF, and the lid is put on the cistern by passing the axes through the tubes HH. The handle P is put upon the empty axis, and the pulley Q upon the axis on which the cloth is rolled, and the cord R, with the weight T, is put round it and over the pulley S. The use of the friction, produced by this weight, is to make the cloth wind tight upon the other axis. But as the effect of the weight will increase as one cylinder increases and the other lessens, Mr Rupp recommends that three or four weights be suspended on the cord, which may be taken off gradually as the person who works the machine may find it convenient. As the weights hang in open hooks, which are fastened to
Oxy-Muri-the cord, it will be little or no trouble to put them on
atic Acid. and to remove them.
Things being thus disposed, the bleaching liquor is to be transferred from the vessels in which it has been prepared into the apparatus, by a moveable tube passing through the tube I, and descending to the bottom of the cistern. This tube being connected with the vessels, by means of leaden or wooden pipes provided with cocks, hardly any vapours will escape in the transfer. When the apparatus is filled up to the line a, the moveable tube is to be withdrawn, and the tube I closed. As the liquor rises above the edge of the rim G, and above the tubes HH, it is evident that no evaporation can take place, except where the rim does not apply closely to the sides of the box; which will, however, form a very trifling surface if the carpenter's work be decently done. The cloth is now to be wound from the axis L upon the axis K, by turning this; and when this is accomplished, the handle P and pulley Q are to be changed, and the cloth is to be wound back upon the axis L. This operation is, of course, to be repeated as often as necessary. It is plain, that by this process of winding the cloth from one axis upon the other, every part of it is exposed, in the most complete manner, to the action of the liquor in which it is immersed. It will be necessary to turn, at first, very briskly, not only because the liquor is then the strongest, but also because it requires a number of revolutions, when the
axis is bare, to move a certain length of cloth in a given Oxy-Muri-
atic Acid. time, though this may be performed by a single revolution when the axis is filled. Experience must teach how long the goods are to be worked; nor can any rule be given respecting the quantity and strength of the liquor, in order to bleach a certain number of pieces. An intelligent workman will soon attain a sufficient knowledge of these points. It is hardly necessary to observe, that, if the liquor should retain any strength after a set of pieces are bleached with it, it may again be employed for another set.
With a few alterations, this apparatus might be made applicable to the bleaching of yarn. If, for instance, the pulley O were removed from the end of the axis K, and fixed immediately under the tube H;—if it were perforated in all directions, and tapes or strings passed through the holes, skains of yarn might be tied to these tapes underneath the pulley, so as to hang down towards the bottom of the box. The apparatus being afterwards filled with bleaching liquor, and the axis turned, the motion would cause every thread to be acted upon by the liquor. Several axes might thus be turned in the same box, and being connected with each other by pulleys, they might all be worked by one person at the same time; and as all would turn the same way and with the same speed, the skains could not possibly entangle each other.