Safely of Steam Boats. 147 



The engineer (commonly so called) is not perhaps the person to 

 whose negligence these calamities are chargeable, but rather to the 

 Fireman ; who, besides throwing in the fuel, has to see, by the 



cocks 



This station 



is extremely arduous, and he is to an unusual degree exposed to the 

 temptation of drinking inordinately. The boiler is usually made of 

 large diameter, and with an inside flue, which is intended to be al- 

 ways covered by the water- This is not the strongest form in which 

 a boiler can be made, but is that which takes up the least room. 

 This Hue may, not only from the inattention of the fireman, but from 

 any accidental obstruction or disorder of the supply pump, get un- 

 covered, or the water low, when it will become red hot, soft, flexible, 

 thin, and weak ; and as this part of the boiler is out of sight, this may 

 happen (to a degree short of giving way) frequently in the course of 

 a season : and although the proper quantity of water may be pre- 

 sently regained, still the hidden weakness thus caused remains, and 

 may show itself fatally at some subsequent period. If it were ask- 

 ed, how is the thickness of a boiler in all its parts, after being some 

 length of time in use, ascertained to be sufficient ? The usual method 

 is to strike it with a hammer, wherever accessible, trusting to the in- 

 dications given by the sound of the blow. In the making of boil- 

 ers, it is possible that the plates may have flaws not quite obvious 

 enough for their rejection, and it is not uncommon for rivets to break 

 by the expansion of the metal, if not made of very good iron. Boil- 

 ers may be kept in use too long, when the business is not very prof- 

 itable. It is an expensive job to displacethem for repairs, and it is 

 natural to defer it as long as may be safe. Steam boats are some- 

 times sold at auction, to close a concern, when although the age of 

 the boiler may be told, its condition cannot be so easily known. 



It is commonly supposed that the safety valve is an effectual safe- 

 guard ; and it is so, in a well made and well managed engine. The 

 intention of it is to allow the steam to vent itself when it gets so 

 strong as to lift the weight hung upon the lever of the valve. But it 

 has been known to be fatally overloaded. Besides it is not calcu- 

 ated to give passage to a great and sudden increase of steam. And 

 such sudden and great increase may happen when the flue has been 

 long enough bare to get red hot, and water is suddenly restored in 

 sufficient quantity to receive its accumulated heat. It is well known 

 that water boils at 212° of Fahrenheit. But it is not so generally 

 known that after this degree of heat, every additional 30 degree?, 



