118 



the second member of the ratio we can achieve our object by in- 

 creasing the first member, i.e., by adding to the water an appro- 

 priate amount of lime. This combines with the second equivalent 

 of carbonic acid and thus becomes insoluble. The removal of the 

 extra dose of carbonic acid causes the carbonate of calcium 

 originally in solution to become insoluble also so that it separates 

 out as well. After due settling and straining the water is softened 

 and fit for use. Thus one compound of calcium is used as a remedy 

 for a defect in the water due to the presence of another compound. 



Let us think again of a bottle of soda water. The liquid it 

 contains consists of water charged with carbonic acid gas and con- 

 taining a small quantity of bicarbonate of soda. The water was, 

 very likely, softened by the lime process. The carbonic acid was 

 probably got by acting on chalk with acid. The third constituent, 

 bicarbonate of soda, although it contains no calcium, was certainly 

 made by a process in one or more stages of which calcium car- 

 bonate played an important part. The alkali manufacture is one of 

 the very largest and most important of the world's chemical in- 

 dustries. It may be taken to include the production of carbonate 

 and bicarbonate of soda and of caustic soda. In 1900 the total 

 production of these substances had reached the imposing figure 

 of one and a half millions of tons and since then it has no doubt 

 largely increased. To describe the various processes employed 

 would be straying beyond the legitimate limits of the present 

 lecture, but I may say that chalk or limestone is used in them all. 

 Roughly, each pound of soda turned out requires a pound of lime- 

 stone to be used in the manufacture. Thus some two million tons 

 of calcium carbonate are used annually in the alkali manufacture ; 

 an impressive example of the application of the lime compounds 

 In the service of man. 



We have seen that all the contents of the soda-water bottle 

 had some bearing on our subject and this is quite as much, or 

 more, the case with the bottle itself. In the concluding lecture 

 of the " Silica Series" I dealt with the manufacture of glass so 

 that I need only now remind you that ordinary bottle glass con- 

 tains something like 20 per cent, of lime. Another industry in 

 which enormous quantities of limestone are required is that of 

 iron smelting. The most important of our English ores of iron 

 contains much clay. This clay is practically infusible and the iron 

 could not be readily, if at all, separated from it were it not for the 

 intervention of limestone. At the high temperature of the blast 

 furnace limestone and clay act on' each other and an easily fusible 

 slag is formed. About half a ton of limestone is required for every 

 ton of pig iron that is produced. As a single large modern furnace 

 may produce 70,000 tons of iron per annum we can form a rough 

 estimate of the immense quantity of limestone used for this pur- 

 pose alone. 



Another large-scale use of lime is in the manufacture of 

 bleaching powder, perhaps better known as Chloride of Lime. 

 This substance, through its properties as a disinfectant, tends to 



