142 FIRESIDE SCIENCE. 



TIN PIPE. 



Pure " block-tin," so called, supplies a good metal 

 from which to construct water-pipes. As noticed 

 above, it has the disadvantage of being readily acted 

 upon by some waters ; but this is purely an econom- 

 ical matter, as the salts of tin are not specially poi- 

 sonous, and no harm can result from its solution in 

 water. Block-tin pipes are quite expensive; but 

 this is a small matter to many, and we recommend 

 the use of tin pipes in cases where cost is not re- 

 garded. Of course, there are many who cannot 

 afford them, and a cheaper and equally safe 

 water-pipe is needed. Those who seek a cheaper 

 pipe must not be deceived by the clean, attractive 

 appearance of the 



GALVANIZED IRON PIPE. 



Iron pipes are "galvanized" by immersing the 

 common gas-pipes in hydrochloric acid, and then 

 immediately placing them in a bath of melted zinc. 

 The zinc amalgamates with the surface of the iron, 

 forming a superficial covering of the metal. This 

 is a very cheap process, and was originally adopted 

 with the view of preventing gas-pipes from rusting 

 in damp places. Such pipes were never designed 

 to be used for the conveyance of water, even by the 

 manufacturers ; and how any one ever ventured to 

 use them for that purpose is a matter not easily un- 



