Boiler Explosions. 



163 



Fig. 8. Often, when very impure water is used, boil- 



ers are attacked by internal corrosion. Usually 

 it is found at the edge of the sheets, along the 

 seams and around the rivet heads. Sometimes 

 different plates in the boiler will be corroded, 

 while others will be found in good condition. 

 "With all this evidence of the dangerous pro- 

 cesses going on both without and within a boil- 

 er, it seems very plainly indicated, that too 

 much care and attention cannot be given them. 

 Marine boilers are of the most dangerous class, 

 but they seldom explode. The reason is evi- 

 dent. First-class men, and none others, are 

 placed in charge of them. The statistics show 

 that in the decade from 1865 to 1875, there 

 was an average of about one explosion every 

 three days, and it would seem that the public 

 had the right to demand some system whereby 

 In a little higher grade of intelligence could be 



placed in charge of these, now, indispensable 

 agents of the public service. 



From the use of impure water results a pro- 

 cess called "pitting." Small holes quite near 

 together are eaten into the plates, and often a 

 pitted plate and a sound one will be found side 

 by side. This is probabij^ due to a chemical 

 difference in the iron, and the pitting may be 

 caused by galvanic action. Pitted plates re- 

 semble very much the partly consumed zincs 

 from a battery. Experiments were made with 

 pieces of iron cut from pitted plates, and 

 those which were not, taken' from the same boiler and placed in a 

 bath of acidulated water, when connected with a galvanometer, 

 the pieces excited sufficient action to sensibly deflect the needle. 



Fig. 7 * shows a case of pitting, and fig. 8 represents a corroded 

 brace or stay rod, so much of which is destroyed that it became 

 entirely useless. 



*Fig8. 7 and 8 are taken fromlEeports of Hartford Boiler InBurance Company. 



