72 Agricultural Chemistry. 



Another method is to boil the water either in the open air or 

 in special heaters. This decomposes the bi-carbonates, drives 

 out the excess of carbon dioxide and the normal carbonates of 

 magnesium and calcium settle out as precipitates. 



Permanent hardness is less easily remedied, for in every case 

 the treatment of the water leaves in solution some substance more 

 or less deleterious. Sodium carbonate and barium chloride are 

 the materials in common use. A recent suggestion calls for the 

 use of sodium bi-chromate within the boiler, as a corrective for 

 both temporary and permanent hardness. It is claimed that the 

 calcium and magnesium chromates precipitate in the boiler as a 

 loose, non-adherent mass, which is removed by "blowing off" 

 daily. It is further claimed that the free chromic acid does not 

 attack the boiler iron. Much care is necessary in order to avoid 

 an excess of any chemical added. As a rule the water should 

 be treated before it goes into the boiler. But if the scale-forming 

 material does not exceed 150 parts per million, the purification 

 may be done in the boiler itself, followed by daily "blowing off." 



A great many proprietary "anti-scale" preparations are sold, 

 many of which are of no particular value. Most of them are to 

 be used inside the boilers. Some are supposed to act chemically 

 on the impurities and others are mechanical, preventing the ad- 

 herence of scale. The former usually contain soda-ash, caustic 

 soda, barium hydroxide, or sodium phosphate. Tannin in the 

 form of sodium tannate, is sometimes employed, by which the 

 calcium and magnesium are separated as tannates. 



In a drinking water the presence of calcium compounds, except 

 perhaps in excessive amounts, is not objectionable. Indeed, it is 

 often advantageous, furnishing a portion of the lime necessary 

 for the building up of the hard parts, such as bones or shells, of 

 the animal. Moreover, in many cases water is delivered through 

 lead pipes and soft waters, especially if they contain vegetable 

 acids, as for example peaty waters, attack and dissolve the lead, 

 and often to such an extent as to cause lead poisoning in those 



