60 REPORT—1840. 
obviated, while the bleaching power still remained uninjured. They 
took out a patent for this discovery ; but it was infringed upon by the 
Lancashire bleachers; a law-suit was the consequence, and the patent 
was destroyed. It was then that Mr. Macintosh tried whether chlorine 
would not be absorbed by slacked lime. The trial succeeded: a com- 
pound was formed, which readily dissolved in water, and the solution 
of which possessed great bleaching power; a patent was taken out for 
the manufacture of this dry powder, which the patentees distinguished 
by the name of bleaching powder. This patent was not infringed ; 
the sale of it was at first small, and it was overlooked by the bleachers. 
The consequence was, that the patentees had leisure to perfect their 
method of preparing it, and to become able to sell it at so low a price, 
that it gradually superseded all the old methods of bleaching by chlo- 
rine. The process may be seen at St. Rollox in great perfection, and 
on a very large scale. The requisite mixture of common salt, binoxide 
of manganese and sulphuric acid, is put into a leaden still, and the 
chlorine evolved passes through leaden tubes into air-tight stone 
chambers, the bottoms of which are covered with a stratum of slacked 
lime several inches thick. The lime absorbs the gas as it passes into 
the chamber, and the process is continued till the absorption is 
reckoned sufficient. Bleaching powder, supposing it pure, is a com- 
pound of 
i: Chloridesof caleium) we taco wine F 
25 Chiorite ofimerrn ois se '% Parte 10 
SniWatertarSeisinerliet gikver! ohh eS 
20°375 
Half the lime loses its oxygen, and combines with chlorine, consti- 
tuting chloride of calcium. The oxygen combines with chlorine, 
which, in the state of chlorous acid, combines with the other half of 
the lime, constituting chlorite of lime. Two atoms of the water were 
in the slacked lime. The third atom must have come along with the 
chlorine gas, or been absorbed from the atmosphere. 
4. After the chlorine has been extricated, there remains in the still 
a semi-liquid mass, consisting partly of the impurities of the manga- 
nese, and partly of sulphate of soda and sulphate of manganese. If 
the manganese were pure binoxide, and only the quantity of salt and 
sulphuric acid necessary for the decomposition were used, the sulphate 
of manganese (abstracting the water) would weigh nine and a half, 
and the sulphate of soda nine. But in order to save the stills by pro- 
ducing the decomposition with little heat, twice as much sulphuric 
acid is used as is necessary, and this excess is afterwards saturated by 
means of common salt; so that the quantity of sulphate of soda in the 
residue is at least twice as great as that of the sulphate of manganese. 
To get rid of the sulphate of manganese, the residue from the stills is 
fused in a reverberatory furnace at a red heat; this drives off the sul- 
phuric acid, and leaves the manganese in the state of sesquioxide. The 
whole is dissolved, and the insoluble manganese thrown away. The 
solution of sulphate of soda is evaporated to dryness, mixed with small 
