CHLORIDE OF LIME 781 



hydrogen.' Watts's ' Dictionary of Chemistry.' For descriptions of the chlorides, refer 

 to their respective metals. 



The term ' chloride ' is also applied in the arts to a number of bleaching compounds, 

 sucli as ' chloride of lime,' the exact chemical nature of which is still obscure, though 

 it is certain that they are not simple chlorides, or combinations of chlorine with 

 metals. It is now generally believed, that these so-called chlorides of the alkalis 

 and alkaline earths are either compounds or mixtures of true chlorides with hypo- 

 chloritos. 



CHLORIDE OF LIME. The compound so called was first employed in the 

 liquid form as a bleaching agent in 1798; and in the following year the idea suggested 

 itself to Mr. Charles Macintosh, at that time a partner of Messrs. Tenant and Knox, 

 to impregnate quicklime in a dry state with chlorine, and a patent was taken out ac- 

 cordingly. The discovery of the bleaching property of chlorine is due to Berthollet, 

 who announced the fact to the Academy of Sciences in 1785. In the following year, 

 the new method of bleaching was introduced into Great Britain by Mr. Watt. In 1788, 

 Mr. Thomas Henry of Manchester exhibited calico bleached by chlorine, without 

 having any knowledge of the previous experiments of Watt ; and in the following year 

 a detailed method of the process was published by Berthollet. To give some idea of 

 the rapidity with which bleaching is conducted by the improved modern processes, the 

 writer of the article on this subject in the Encyclopaedia Britannica quotes the follow- 

 ing illustration : A bleacher in Lancashire received 1,400 pieces of grey muslin on a 

 Tuesday, which on the Thursday immediately following were returned bleached to the 

 manufacturers at the distance of 16 miles and they were packed up and sent off that 

 very day to a foreign market. . 



It is estimated that the present annual production of chloride of lime in Great Britain 

 and Ireland amounts to 75,000 tons, of the value of three-quarters of a million sterling. 



In the manufacture of chloride of lime, chlorine gas is transmitted at a proper 

 temperature through milk of lime or . over dry slaked lime, the product being thus 

 obtained either as a liquid or as a powder. The different methods of generating the 

 gas will be described under CHLORINE. 



A great variety of apparatus has been at different times contrived for favouring the 

 combination of chlorine with the slaked lime for the purpose of commerce. The 

 simplest construction for subjecting lime-powder to chlorine, is a large chamber 8 or 

 9 feet high, built of sandstone, having the joints of the masonry secured with a cement 

 composed of pitch, resin, and dry gypsum in equal parts. A door is fitted into it at 

 one end, which can be made air-tight by. strips of cloth and clay lute. A window on 

 each side enables the operator to judge how the impregnation goes on by the colour of 

 the air, and also gives light for making the arrangements within at the commencement 

 of the process. As water lutes are incomparably superior to all others where the pneu- 

 matic pressure is small, a large valve or door on this principle might advantageously 

 .bo made in the roof, and two tunnels of considerable width at the bottom of each 

 side wall. The three covers should be simultaneously lifted off by cords passing over 

 a pulley, without the necessity of the workman approaching the deleterious gas, when 

 the apartment is to be opened. A great number of wooden shelves, or rather trays, 

 8 or. 10 feet long, 2 feet broad, and 1 inch deep, are provided to receive the riddled 

 slaked lime, containing generally about 2 atoms of lime to 3 of water. These shelves 

 are piled one over another in the chamber, to the height of 5 or 6 feet, cross bars below 

 each keeping them about an inch asunder, in order that the gas may have free room to 

 circulate over the surface of the calcareous hydrate. 



The alembics for generating the chlorine, which are usually nearly spherical, are in 

 some cases made entirely of lead, in others of 2 hemispheres joined together in the 

 middle, the upper hemisphere being lead, the under one cast-iron. The first kind of 

 alembic is enclosed for two-thirds from its bottom in a leaden or iron case, the interval 

 of two inches between the two being destined to receive steam from an adjoining boiler.. 

 Those which consist below of cast-iron have their bottom directly exposed to a very 

 gentle fire ; round the outer edge of the iron hemisphere a groove is cast, into which 

 the under edge of the leaden hemisphere fits, the joint being rendered air-tight by 

 Koman or patent cement. In this leaden dome there are four apertures, each secured 

 by a water-lute. The first opening is about 10 or 12 inches square, and is shut with 

 a leaden valve, with incurvated edges, that fit into the water-channel at the margin of 

 the hole. It is destined for the admission of a workman to rectify any derangement in 

 the apparatus of rotation, or to detach hard concretions of salt from the bottom. 



The second aperture is in the centre of the top. Here a tube of lead is fixed, which 

 descends nearly to the bottom, and down through which the vertical axis passes. To 

 its lower end the cross bars of iron or of wood, sheathed with lead, are attached, by 

 whose revolution the materials receive the proper agitation for mixing the dense man- 

 ganese with the sulphuric acid and salt. The motion is communicated either by the 



