# t 
Proceedings of the British Association. 49 
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. 
_ Pure bleaching powder is a compound of 
Chloride of calcium, < *" > “Seo! 255%, 
Chlorite of lime, - - S20 ee IG, 
Water, - . - - of 3.376 . 
a 
20.375 
Half the lime loses its oxygen and combines with chlorine, 
constituting 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. Carbonate of soda is obtained from the se- 
mi-liquid mass remaining in the still, and consisting partly of the 
impurities of the manganese, and partly of sulphate of soda, and 
sulphate of manganese. 5. The manufacture of alum is carried 
on at two establishments, one at the Hurlet, about six miles S. 
W. by the Paisley canal; another at Campsie, about eight miles 
off, near Kirkintulloch, on the great canal, and near the foot of 
the Campsie Hills. The alum is made from the shale, which ex- 
ists in great abundance in the exhausted coal beds. This shale is 
a clay mixed with some coal, and with that variety of iron py- 
rites which undergoes decomposition, and is converted into sul- 
phate of iron, by exposure to the air. ‘The sulphate of iron thus 
formed, acts slowly on the clay, and finally converts it into sul- 
phate of alumina. The alum-maker washes this altered shale, 
and obtains a solution of sulphate of iron and sulphate of alu- 
mina. ‘The liquor yields an abundant crop of sulphate of iron, 
which is removed, dried, and sold ata cheap rate. The sulphate 
of alumina does not crystallize till it is mixed with sulphate of 
potash or sulphate of ammonia; because ammonia is a double salt 
composed of three atoms of sulphate of alumina and one atom 
of sulphate of potash or sulphate of ammonia. 6. At Campsie 
alum-works, is prepared the prussiate of potash,a well known 
beautiful yellow salt, crystallizing in truncated octahedrons. The 
manufacture of this salt on the large scale began here. Before - 
7 
Vol. xt1, No. 1.—April-June, 1841. . 
“+ 
‘ + 
Mo, Bot. Garden, # 
¥. 
