Page:The American Cyclopædia (1879) Volume II.djvu/727

 BLEACHING POWDER BLEDOW 707 sheet lead ; or sometimes of stones closely fitted and cemented to each other. The lower por- tion is sometimes made double for the purpose of introducing steam to heat the mixture in the inner vessel. The materials introduced are in the following proportions, rated as if pure, but varying with their impurities: binoxide of manganese, 100 parts; common salt, 150 parts; and sulphuric acid, of specific gravity 1'6, about 185 parts. The temperature is kept at about 180 F., and the materials are kept in agitation by a stirrer, which is made to revolve in the lower part of the vessel. As the gas is evolved, it passes by a lead pipe to the purifier, and into the top of the chamber in which the hydrate of lime is deposited in trays, which are placed upon shelves. Heat is generated by the chem- ical combination ; but it should not be allowed to exceed 62 F., the supply of chlorine being checked to keep the temperature down. For two days the process goes on, when it is stopped, that the workmen may enter with half a set of trays of fresh hydrate of lime to replace an equal quantity which has been exposed four days to the action of the gas, and to stir over that which has been in two days. Half a charge is thus taken out every two days. When well made, it should be a uniform white powder, without lumps, smelling of chlorine, dissolving with little residue in 20 parts of water with alkaline reaction, and attracting moisture very slowly from the air. When pre- pared in a liquid state, the gas is passed into lime water, till this is saturated with it. The solution, for the quantity of lime it contains, is stronger than the dry powder, but it is not so permanent in character, the chlorine sooner escaping from it. Mr. Tennant of Glasgow employs a method devised by Mr. 0. T. Dunlop for liberating chlorine from common salt with nitrate of soda and sulphuric acid. If one equivalent of nitrate of soda and three of chlo- ride of sodium are decomposed by sulphuric acid, nitrous acid, hydrochloric acid, and chlo- rine are generated. The acids are separated by passing all three of the gases successively through sulphuric acid and water. The chlo- rine, not being absorbed by either the acid or the water, may be passed on into the lime chamber. The process of Mr. Weldon consists in neutralizing the residual liquor containing manganese chloride, which is produced in the ordinary process, with hydrochloric acid and manganese oxide, with finely divided carbonate of lime. This produces a neutral mixed solu- tion of chloride of manganese and chloride of calcium, holding in suspension considerable sulphate of lime and small quantities of oxide of iron and alumina. The mixture is then pumped into settling tanks, where these sub- stances subside, leaving the liquor clear, which is then run off into a vessel called the oxidizer. Air is forced through it and milk of lime added until the manganese in the liquor is principally converted into peroxide. This process is now extensively employed. Deacon's process, de- signed to obviate the use of manganese oxide, is founded on the fact that if a mixture of hy- drochloric acid and oxygen is heated in the presence of certain substances, a catalytic force causes the decomposition of the hydrochloric acid, the hydrogen combining with the oxygen, while the chlorine is set free. The gases are passed through a reverberatory furnace heated to 700 or 750 F. over pieces of brick which have been saturated with a solution of sulphate of copper, and dried. The precise chemical constitution of chloride of lime has always been a subject of controversy, which can hardly be held as settled at the present time. Dr. Ure considered the commercial article as a mixture, in no definite proportions, of chlorine and hy- drate of lime, and believed that the more defi- nite compound prepared with dry calcium hy- drate contained chlorine in direct combination with the hydrate. Fresenius regards it as a mixture of calcium chloride, CaCl, and calcium hypochlorite, OaOCl or CaClO 3 ; and this is the view taken by Wagner and others. These opinions, it must be borne in mind, relate to the pure, dry article, and not to the commercial one. The subject has lately been carefully in- vestigated by Kolb (Jahresbericlit, 1867), who finds that the most concentrated preparation which can be produced by saturating dry cal- cium hydrate with chlorine contains 38'5 per cent, of chlorine, 45'8 of lime, and 24'7 of water, in which the water and the whole of the lime are essential constituents. Commer- cial bleaching powder contains more water as well as free lime. Dry chloride of lime is de- composed by water with separation of calcium hydrate and the formation of a solution con- taining chloride and hypochlorite of calcium. Kolb, reasoning from the fact that dry bleach- ing powder and the solution comport them- selves differently under the influence of free chlorine and heat, thinks that the first does not contain a ready-formed hypochlorite, but is a compound which may be represented by the formula CasHsOnCU. Dry chloride of lime, moreover, is completely decomposed by carbo- nic acid with evolution of chlorine, while only half the lime is precipitated from the solution by this agent, with separation of hypochlorous acid, which does not act upon the remaining chloride. Solid chloride of lime in moist air behaves in the same way, from which it appears that bleaching powder, on exposure without the addition of an acid, yields hypochlorous acid and not free chlorine. For the determina- tion of the available amount of chlorine in a given quantity of bleaching powder, see CHLO- BIMETBT. BLEDOW, Lndwlg, a German chess player, born July 27, 1795, died Aug. 6, 1846. He was a teacher of mathematics, and founded the so- called Berlin chess school and the first German journal on chess, Berliner Schachzeitung. He published two small collections of outlines of games, and edited the work of the Syrian chess player Stamma. His extensive collection of