ABOUT COMMON WATER. 841 



stalagmites in our limestone caves. But there is 

 another way of converting the bicarbonate into the 

 carbonate, which is well worthy of our attention, ft 

 will show how a man of science thinks before he ex- 

 periments, and how, by experiment, he afterwards 

 verifies his thought. Bearing in mind that the chalk- 

 springs hold lime in solution as bicarbonate, it is plain 

 that if we could rob this bicarbonate of half its car- 

 bonic acid, we should reduce it to the simple carbonate, 

 which is almost wholly insoluble. 



Think the matter over a little. What we have to 

 combat is an excess of carbonic acid. Lime-water, with- 

 out any carbonic acid, is easily prepared. Suppose, 

 then, that we add to our chalk- water, with its double 

 dose of carbonic acid, some pure lime-water; what 

 would you expect ? You would, at all events, think it 

 probable that the bicarbonate of the chalk-water would 

 give up its excess of carbonic acid to the lime, and 

 assume the condition of the simple carbonate, which, 

 because of its insolubility, would be precipitated as a 

 white powder in the water. And, because chalk is 

 heavier than water, you would conclude that the powder 

 would sink to the bottom, leaving a clear, softened 

 water overhead. Thus reasoned Dr. Clark, of Aberdeen, 

 when he invented his beautiful process of softening 

 water on a large scale. I have myself seen the process 

 applied with success in various chalk-districts in 

 England. 



Let us make a calculation. Every pound of chalk 

 contains nine ounces of lime and seven ounces of car- 

 bonic acid. Dissolved by rain-water, this simple 

 carbonate becomes bicarbonate, where every nine 

 ounces of lime combine with fourteen ounces of car- 

 bonic acid. If, then, a quantity of pure lime-water 

 containing nine ounces of lime be added to these 



