358 On Steam-Engines. [Nov. 



explosions, if not absolutely impossible, are at least extremely 

 rare ; and with which not a single instance of an explosion has 

 occurred in France, since they have been used in that country. 



Such are the mean-pressure engines, of three or four atmo- 

 spheres, made in France, on Woolfe's construction, as improved 

 by Edwards, with boilers four or five times stronger than can 

 be burst by the force of the steam which they have to resist. 



Such also are the high-pressure engines of 10 atmospheres, 

 constructed on the plan of Oliver Evans, of the United States 

 of America. With these engines the boiler is capable of resist- 

 ing ten times the force it is daily subjected to. 



But engines constructed with less care, or managed with less 

 prudence, have occasioned dreadful accidents, especially in 

 Great Britain. 



In France only one accident has ever happened, by which 

 any lives were lost, which were those of two individuals engaged 

 in the service of the engine ; and not one single instance has 

 occurred in that country, in which any damage has been sus- 

 tained by any individuals, from the explosion of a steam-engine 

 on the adjoining premises. 



Although it appears, from the preceding statement, that no 

 one in the neighbourhood of a steam-engine, in France, has 

 ever suffered either in his person or property from any explo- 

 sion, yet the impossibility of such consequences has not been 

 proved ; and the bare apprehension of the danger is a real evil, 

 attendant on the erection of a mean or high-pressure steam- 

 engine in the neighbourhood of a dwelling-house. To reduce 

 that apprehension as much as possible the following precautions 

 should be adopted. 



1. Every steam-engine boiler should be furnished with two 

 safety valves, one of them inaccessable to the workman who 

 attends the engine, the other under his command, in order 

 that he may be able to diminish the pressure on it, as occasion 

 may require. If "he attempt to overload this valve, it will have 

 no effect, since the steam will find vent through the other, 

 which is out of his reach. 



The reporter, M. Dupin, suggests in this place, that if any 

 apprehension of danger be entertained, from the possibility of 

 the inaccessable valve becoming fixed by rust, or negligence, 

 it may be obviated, by fixing in the upper part of the boiler two 

 plugs of fusible metal, formed of such an alloy, as to melt at a 

 few degrees above the working temperature of the steam. One 

 of these plugs is to be considerably larger than the other, and 

 to be made of a rather less fusible alloy, so that if the steam 

 does not escape with sufficient rapidity on the fusion of the 

 smaller, it may. have ample room to fly off, as soon as the 

 larger has given way. The temperature, at which the least 



