116 



Drinking- Water and some of its Impurities, 



and also the constituents of the air. Water containing 

 carbonic acid in solution has the property of holding in 

 solution quantities of certain salts that would not other- 

 wise be dissolved. If this carbonic acid be driven off by 

 boiling, a precipitate of carbonate of lime is formed, and 

 the water loses part of its hardness. That which remains 

 is called permanent hardness, while that which dis- 

 appears is called temporary hardness, and is due to the 

 carbonates. The permanent hardness is due chiefly to 

 sulphate of lime, chloride of lime and to magnesian salts. 

 These are all highly objectionable. 



As heat liberates carbonic acid we would naturally infer 

 river or lake water to be softer in summer than in winter, 

 and this we find to be true. The hardness of the water 

 also varies with the height of the stream. After a rain, 

 when soft rain water in large quantities has run in, the 

 stream is softer, and when it is low the water is harder. 

 This would account for the greater hardness of the water 

 in the winter, for there is no soft rain water flowing in, 

 the river being almost entirely supplied from springs. 

 The following table shows the hardness of the Mohawk at 

 Schenectady for each day during the month of March, 

 1877 with the height of the river above low water for the 

 first two weeks. 



Date. Hardness, Height of river. 



Mar. 1. .. .12°. 5 1 ft. 



" 2... .12.3 1 " 



" 3 12 1 " 



" 4 13.5 1 " 



5 13.5 2 " Gin, 



" 6... 



..13.5.... 



. ...3 " 



0" 





..13 



2 " 



10 " 



" 8... 



..12.5.... 



2 " 



10 " 



" 10... 



..11 



17 " 



2" 



*' 11... 



..10 



....11 " 



2" 



" 12... 



..10 



....10 " 



0" 



" 13 . 



..11 



, , 8 " 



7" 



" 14... 



..11.4... 



7 " 



7 " 



Date. Hardness. Height of river. 

 Mar. 15 11°.6 6 ft. 3 in. 



16 . 



14 .6 



17 , . 



.13. 



18... 



13. 



19, . . 



,13. 



20 ,. 



12. 



21 .. 



..12. 



22.. 



..11.5 



23, .. 



..11. 



26 .. 



..10. 



27 , 



. 10. 



28... 



..10. 



