278 GENERAL SCIENCE 



Soft Water. Some waters act on lead pipes, especially soft 

 well waters which contain much dissolved carbonic acid. If a water 

 causes a coating to form on the interior of a lead pipe, there is little 

 or no danger of lead poisoning, because the coating protects the 

 metal; but if the lead stays bright it indicates that the metal is 

 being dissolved, a fact which will make the water dangerous to use. 



Common Salt in Water. Water polluted by the drainage of a 

 house contains a small amount of salt. All water contains some 

 salt, but the amount of salt found in water polluted in this way is 

 greatly increased. 



Test for Salt.* Place 50 cubic centimeters of water in each of two small flasks. 

 Add a few drops of dilute potassium chromate solution. Color the contents of 

 the two flasks as nearly alike as possible. Add to one flask a standard silver solu- 

 tion drop by drop from a pipette showing cubic centimeters. Frequently agitate 

 the glass. The number of cubic centimeters required to produce the first 

 tinge of red in the flask denotes the number of parts of chlorin (salt) in 100,000 

 parts of water. The slight tinge of red is better seen by comparing the con- 

 tents of the flask with the contents of the flask to which the silver solution has 

 not been added. 



If the water contains more than five parts of chlorin per 100,000, 

 contamination from sewers or sink drains is possible. 



Sea coast towns have a large percentage of salt in the water. The percentage 

 of salt in such places may be obtained from the State Board of Health. 



A standard silver solution is prepared by dissolving 36 grains (2.3944 grams) 

 of silver nitrate in a liter (1000 cubic centimeters) of distilled water. 



Hard and Soft Water. Water is often called hard if soap suds 

 will not form in it. It is very difficult to clean clothes in hard water. 

 There are two kinds of hardness, (1) temporary hardness, due to 

 calcium bicarbonate which can be removed by boiling the water 

 and causing calcium carbonate to form at the bottom of the dish; 

 (2) permanent hardness, which is caused by sulphates and chlorides 

 of calcium and magnesium. This is called permanent hardness 

 because boiling will not render the water soft. If washing soda or 

 soda ash is added to such water, the effect is to soften it. 



Hard water often causes scales to form on the inside of kitchen 

 and factory boilers. This may prove dangerous, since heat is not 



* By Allyn. 



