784 CHLORIDE OF LIME 



the experimental laboratory plan described above. In all such apparatus we should 

 avoid giving any pressure to the tubes or vessels, and should not therefore dip the ex- 

 tremities of the gas-pipes beneath the surface of the liquid, but rather facilitate the 

 combination of the chlorine and the lime, by enlarging the surfaces of contact and by 

 agitating. Intermediate vessels containing water, or the chemical cascade of M. Clement, 

 are very useful for absorbing any muriatic acid which may be disengaged along with 

 the chlorine, and thereby preventing the needless formation of muriate of lime in the 

 chambers or cisterns of impregnation. 



When the solution of the chloride of lime is mixed with hydrate of lime, it bears, 

 without decomposing, a pretty high temperature, provided it be not too long continued ; 

 it may even, in certain cases, be raised to near the boiling point without suffering a 

 marked loss of its discolouring power; but when the chloride is deprived of that excess 

 of lime, it is decomposed in a short time, even at a heat of 110 F. 



When chlorine is admitted to milk of lime, it infallibly produces some muriate of 

 lime ; but the quantity is kept at a minimum by constantly presenting an excess of 

 lime to the gas with the agitator, and by keeping the temperature as low as possible. 

 Hence the influx of gas should not be so rapid as to generate much heat. An automatic 

 agitator, moved by steam or water power, is therefore much better than one driven by 

 the hand of the operator, who is apt to intermit his labours. 



If the liquor becomes hot at the end of the process, it should be immediately drawn 

 off into large stone bottles and cooled. The rose colour, which sometimes supervenes, 

 is duo to a minute quantity of manganese : the strongest liquid chloride of lime that 

 can be prepared will not discolour more than 80 times its volume of Gay-Lussac's 

 indigo test. 



In the year 1846, Mr. Pattinson patented an improved mode of manufacturing 

 chlorine. In this process he made use of a stone vessel or generator, enclosed in a 

 double iron vessel. The hydrochloric acid, specific gravity 1*16, is poured into the 

 generator, and on a grating or false bottom is placed the binoxide of manganese in 

 lumps. The temperature of the contents of the generating vessel is then raised to 

 180 F., by means of steam, made to circulate between the stone vessel and the iron 

 casing. This heat is continued for about 18 hours ; and then, by means of a suitable 

 pipe passing to the bottom of the generator, steam, under a pressure of 10 Ibs. to the 

 inch, is injected into the vessel for about two minutes, and this is repeated every half 

 hour for about six hours. In this process no mechanical agitation is required, as the 

 steam enters with sufficient force, under the pressure above mentioned, to effect the 

 requisite agitation of the contents, and by clearing the lumps of manganese from all 

 adhering matters, expose a fresh surface continually to the action of the acid. 



In carrying this process into practical operation, Mr. Pattinson found that the 

 apparatus is liable to be completely deranged, and the iron vessel destroyed by the 

 action of the hydrochloric acid, if the stone generating vessel should happen to get 

 broken; to obviate which inconvenience, and to enable the generator to be used 

 though in a broken condition, the inner iron vessel is perforated ; and the spaces 

 between the two iron vessels, and between the inner iron vessel and the stone gene- 

 rator, are filled with coal-tar, or pitch, thickened by boiling to such a consistence as 

 to be tough, but not brittle, when cold. Steam, circulating through a coil of pipe 

 passing between the iron vessels, serves to maintain the tar at the requisite degree of 

 heat ; and in the event of the breakage of the stone generator, the liquefied tar flows 

 into the fissure, and prevents the escape of the hydrochloric acid into the steam 



Chlorine-stills of metal or of earthenware, though used evennowinmanv continental 

 works, have been generally displaced in this country by vessels of sandstone. In 

 Lancashire they are usually constructed of Yorkshire flags, cemented together by a 

 mixture of tar and clay, while on the Tyno they are cut out of solid blocks of stone, 

 and rendered impervious on the surface by being boiled in coal-tar. 

 . The receivers in which the chlorine acts on the lime are usually constructed either 

 of stone slabs or of sheet lead supported on timber framework. The receiving 

 chambers are fitted with shelves on which the slaked lime is conveniently exposed in 

 layers for absorption of the chlorine. In other forms of apparatus the lime is placed 

 in a series of pots or in rotating barrels. The absorption of chlorine is accompanied 

 by evolution of heat, but as chlorate of lime is formed at a high temperature the 

 gas is admitted but slowly and the temperature thus maintained sufficiently low to 

 avoid formation of the chlorate. 



Several proposals have been made for utilising the waste liquors from the chlorine 

 stills, most of which aim at reproducing oxide of manganese which may be again 

 available for the generation of chlorine. 



A method of treating the residuum was patented in 1855 by Mr. C. Tennant Dunlop. 



