Dr. U re on Chloride of Lime. 17 



to 14 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 1.5. But, 

 indeed, this dilution is seldom actually made, for the manufac- 

 turer of bleaching-powder almost always prepares his own sulphu- 

 ric acid for the purpose, and therefore carries its concentration 

 no higher in the leaden boilers than the density of 1.65, which, 

 from my table of sulphuric acid, indicates l-4th of its weight of 

 water, and therefore l-3d more of such acid must be used. 



The fourth aperture, I have said, admits the eduction pipe. 

 This pipe is afterwards conveyed into a leaden chest, or cylin- 

 der, into which all the other eduction pipes also terminate. 

 They are connected Avith it simply by water-lutes, having a 

 hydrostatic pressure of 2 or 3 inches. In this general diverso- 

 rium 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 led 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 around. 



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

 making good marketable bleach ing-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 here an alternatino- 

 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 chlorine, 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 ; thus, to my knowledge, very superior 

 bleaching-powder is manufactured, and thus the chlorine may 

 be suflfered to enter in a pretty uniform stream. But for this 

 Vol. XIII. C 



