Perkins"* Steam Engine. 53 



pump which forced out, from under the pressure valve, into 

 the receiver, a corresponding quantity of heated water, and 

 this instantly flashed into steam ; which from its having igni- 

 ted the hemp cord, that covered the steam-pipe, ten feet from 

 the generator, must have been at a temperature of at least, 

 8000 degrees, which would be equal to about 800 atmos- 

 pheres ; but, from want of water to give it its necessary den- 

 sity, the indicator showed a pressure of about five atmos- 

 pheres. Whether the pressure of the steam, which was 

 rushing through the steam-pipe, was at 5 or 100, or more 

 atmospheres, the steam-pipe kept at the high temperature 

 before mentioned ; which I attributed to the steam being^ 

 surcharged whith caloric. The pump was now made to in- 

 ject a much larger quantity of heated water, and the indica- 

 tor showed a pressure of from 50 to 80 atmospheres ; the 

 throttle valve being partly opened, it soon expanded, to the 

 former pressure of about 5 atmospheres. The water was then 

 injected again and again, and the indicator was observed to 

 oscillate at each stroke of the pump, from 5 to between 40, and 

 100 atmospheres, according to the quantity of water injected ; 

 clearly showing that at this reduced pressure, there was a 

 gr€at redundancy of heat, with little elastic force. It soon 

 occurred to me, that to this might be traced the true cause 

 of the tremendous explosions, that suddenly take place, in 

 low, as well as in high pressure boilers. 



There are many instances, where, immediately before one 

 of these terrific explosions had taken place, the engine labor- 

 ed ; showing evidently a decrease of power in the engine. 

 To illustrate the theory of sudden explosions, let us suppose 

 the feed pipe, or pump, to be choked ; in this case, the water 

 would soon sink below some parts of the boiler, which should 

 be constantly covered by it, thus causing them to become 

 heated to a much higher temperature than the water. The 

 steam now being in contact with the heated metal, readily 

 takes up the heat, and becomes surcharged with it.* Since 



* Practical engineers have frequently witnessed the destruction of 

 the packing of pistons, by their becoming charred, although the steam 

 issuing was in contact with the water, the temperature of which did 

 not exceed 230 degrees. It is very evident, that this steam was sur- 

 charged with heat, and was much above the temperature of the water 

 upon which it was reposing, and in a suitable state to produce explo- 

 sion, had the water been allowed to rise with the steam, by drawing it 

 off faster than it was generated. 



