782 CHLORIDE OF LIME 



hand of a workman applied from tamo to time to a winch at top, or it is given by con- 

 necting the axis with wheel work, impelled by a stream of water or a steam-engine. 

 The third opening admits the siphon-formed funnel, through which the sulphuric acid 

 is introduced ; and the fourth is the orifice of the eduction-pipe. The fourth aperture 

 admits the eduction-pipe. This pipe is afterwards conveyed into a leaden chest or 

 cylinder, in which all the other eduction-pipes also terminate. They are connected with 

 it simply by water-lutes, having hydrostatic pressure of 2 or 3 inches. In this general 

 diversorium the chlorine is washed from adhering muriatic acid, by passing through 

 a little water, in which each tube is immersed, and from this the gas is let off by a 

 pretty large leaden tube, into the combination-room. It usually enters in the top of 

 the ceiling, whence it diffuses its heavy gas equally round. 



Four days are required, at the ordinary rate of working, for making good marketable 

 bleaching-powder. A more rapid formation would merely endanger an elevation of 

 temperature, productive of muriate of lime, at the expense of the bleaching quality. 

 But skilful manufacturers use hero an alternating process. They pile up, first of all, 

 the wooden trays only in alternate shelves in each column. At the end of two days 

 the distillation is intermitted, and the chamber is laid open. After two hours the 

 workman enters, to introduce the alternate trays covered with fresh hydrate of lime, 

 and at the same time rakes up thoroughly the half-formed chloride in the others. The 

 door is then secured, and the chamber, after being filled for two days more with chlo- 

 rine, is again opened, to allow the first set of trays to be removed, and to be replaced 

 by others containing fresh hydrate, as before. Thus the process is conducted in regular 

 alternation; very superior bloaching-powder is manufactured, and the chlorine 

 may be suffered to enter in a pretty uniform stream. But for this judicious plan, 

 as the hydrate advances in impregnation, its faculty of absorption becoming 

 diminished, it would be requisite to diminish proportionately the evolution of chlorine, 

 or to allow the excess to escape, to the great loss of the proprietor, and, what is of 

 more consequence, to the .great detriment of the health of the workmen. 



According to M. C. H. Mene (' Comptes Bendus,'.Nov. 22, 1847), chloride of lime may 

 be prepared almost pure, and instantaneously, by pouring upon slaked lime, water satu- 

 rated with chlorine. The chlorine is absorbed the moment the liquid comes into con- 

 tact with the lime, and if the supernatant water is immediately decanted, and the lime 

 remaining at the bottom of the vessel saturated by frequent repetition of the treatment 

 with chlorine water, perfectly pure chloride of lime is obtained. Labarraque finds that 

 the absorption of chlorine by moistened hydrate of lime is greatly facilitated by mix- 

 ing it with Jgth of its weight of common salt. 



Manufacturers differ much from each other in the proportion of their materials for 

 generating chlorine. In general, 10 cwt. of salt are mixed with from 10 to 14 cwt. of 

 manganese, to which mixture, after its introduction into the alembic, from 12 to 14 cwt. 

 of Sulphuric acid are added- in successive portions. That quantity of oil of vitriol must, 

 however, be previously diluted with water, till its specific gravity becomes about 1-6. 

 But, indeed, this dilution is seldom actually made, for the manufacturer of bleaching- 

 powder almost always prepares his own sulphuric acid for the purpose, and therefore 

 carries its concentration in the leaden boilers no higher than the density of 1 '65, which, 

 from Dr. Ure's table of sulphuric acid, indicates ^th of its weight of water, and there- 

 fore rd more of such acid must bo used. 



The manufacturer generally reckons on obtaining from one ton of rock-salt, employed 

 as above, a ton and a half of good bleaching-powder. But the following analysis of 

 the operation will show that he ought to obtain two tons : 



When a mixture of sulphuric acid, common salt, and black oxide of manganese are 

 the ingredients used by the manufacturer of bleaching-powder, the absolute propor- 

 tions required by theory are : 



1 atom chloride of sodium .... 58*5 . . 29 - 75 



1 atom binoxide of manganese .... 43*5 . . 21*25 



2 atoms oil of vitriol 98-0 49-00 



200-0 100-00 



and the products ought to be : 



1 atom chlorine disengaged .... 35'5 17'75 



1 atom sulphate of soda . . . . 71-0 



1 atom sulphate of manganese .... 75'5 



2 atoms water 18'0 



35-50 

 37-75 

 2-00 



200-0 100-00 



These proportions are, however, very different from those employed by the manu- 

 facturers ; and they ought to be so, on account of the impurity of their oxide of man- 



