Two methods of applying pearl-ash to the pur poses of bleaching, are generally followed. These methods are called Boiling and Bucking.
Boiling needs no description. The alkaline ley and the goods are put together into a boiler, and the whole kept at the boiling temperature for the re quisite length of time.
Bucking is somewhat more complicated. It con sists in making the alkaline ley, raised to a boiling heat, to pass repeatedly through the goods. Various modes of performing this process are followed in different bleaching-houses. But they may be all re. duced to one or other of the following three : 1. The goods are placed loosely in a proper vessel, the heated ley is made to run upon them, and to pass through them. As it comes to the bottom of the vessel containing the goods, it is pumped back again into the boiler, where it is heated a second time, and then made to pass through the goods as before. This process is repeated as often as is thought re quisite. 2. The alkaline solution is put into the bot tom of a large boiler, having a platform of wood, with holes through it, placed a little way above the surface of the ley. Through the middle of this platform there passes a pipe of a convenient size, the lower end of which reaches nearly to the bottom of the boiler, being immersed deep in the ley, while the upper end rises as high as the mouth of the boiler. The goods are placed upon the platform, and round the tube within the boiler to a convenient height. When heat is applied to the boiler, the steam gene rated is prevented from making its escape by the wooden platform and the goods. It, therefore, acts upon the surface of the ley, and forces it to ascend through the tube. A kind of umbrella is suspended over the top of the tube, which assists in spreading the ley over the surface of the goods. By this con trivance, it is made to spread over and trickle down through the goods, till it gets again to the bottom of the boiler, to be heated and forced up by the steam as formerly. This method is more efficacious than simple boiling, because the temperature of the ley is heated some degrees higher than 212°, which has a considerable effect upon the goods.
The following are sections of the vessels used for these two different methods of bucking : This figure shows the vessels employed, when the ley is simply pumped back into the boiler. A is the boiler
for heating the alkaline ley. B is the large wooden vessel in which the goods are placed. C the cock and pipe, by means of which 'the ley is con veyed upon the goods. D a square box designed for spreading the ley over the goods within the vessel B. E the pump for raising the liquor again out of the vessel B, from which it is conveyed by the spout I back again into the boiler. F is the furnace for heating the ley. G represents the false bottom of the wooden vessel, full of holes, for the passage of the ley when it has run through the goods. H is a round wooden staff, which completely fits a hole at the bottom of the bucking vessel. It is called a duck, and is intended to be pulled up whenever the spent alkaline liquor is to be run off.
This figure represents the second kind of bucking apparatus. A is a metallic boiler to be fixed in brick work, as in the preced ince figure. BB is the ton CI part of wood, called a crib, with the bottom full of holes. In this, the goods are placed one above another, often a mounting to many hun dred pieces at one ope ration. C is the pipe through which the leys boil up, and dd is the umbrella suspended ver the pipe, for the purpose of spreading the ley more effectually over the method of bucking is a modification of the second. It is considered as preferable, and is perhaps most generally used by experienced and ex tensive bleachers. The platform and its ascending pipe are placed, not in the boiler, but in a conve nient tub or cistern. The requisite quantity of ley is put into the cistern below the platform. A tube into it, which conveys steam from a steam oiler, in such quantity as first to heat up the ley to the boiling point, and then to force it up through the central tube, to be deposited over the surface of the goods, and to filter through them into the space below the platform. This method of bucking so nearly resembles the last, that the nature of the vessel employed will be easily understood without a figure.