Proceedings of the British Association. 49 



leaden tubes into air-tight stone chambers, the bottoms of which 

 are covered witli a stratum of slacked Hme several inches thick. 

 The hme 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, - - - - 7. 



Chlorite of lime, - - - - 10. 



Water, 3.375 



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 alu7n 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 at a 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 



Vol. XLi, No. 1.— April-June, 1841. 7 



