1874.] -07 [Cresson. 



B.— Experiments Upon Hot Plates. 



The fampl s employed were cut from the crown-sheet bars of the 

 exploded boiler. To ascertain their specific heat, and the amount of heat 

 they were capable of imparting to water in a given time, the samples were 

 heated in a mercury bath at various temperatures, and then plunged into 

 a weighed amount of water and the rise of temperature carefully ascer- 

 tained by a thermometer graduated to xV° Ft. 



To ascertain the amount of heat imparted by the iron in a given time, 

 the samples were immersed by securing them to a cross-arm fixed to a 

 heavy pendulum of such length as to vibrate in the desired time and 

 averaging the results of many observations. 



As these experiments were to ascertain the lowest probable capacity of 

 the iron in the crown-sheet for storing and giving out heat, no great care 

 was taken to prevent radiation of heat from the iron in its passage from 

 the mercury bath to the water, nor of radiation from the water bath dur- 

 ing the experiment ; the results do not, therefore, by any means, express 

 the full amount of heat to be derived from the samples. 



Calculations of the amount of steam generated in a given time by iron 

 under the conditions stated, must therefore fall short of the practical 

 effect produced, and if the conditions assumed for experiment show that 

 steam could have been generated in sufficient quantity and with sufficient 

 rapidity to have destroyed the boiler, we can safely conclude that the 

 actual destructive effect was greater than that expressed by our results. 



The specific heat of iron is given in the tables at an average of 0.1200 

 that is, that eight times as much heat is required to raise one pound of 

 water through a given number of degrees as will suffice to raise one 

 pound of iron through a similar number of degrees. For example, 8 lbs. 

 of iron losing lOOO Ft. of temperature will elevate the temperature of 1 lb. 

 of water 100° Ft. By the formula : 



Wt. of Water (J^PP-.^^ Water-Temp, of Water) 

 V before immersion alter immersion / 

 . '■ =S. H. 



Wt. of Iron /Temp, of Iron — Temp, of Iron \ 

 ^before immersion after immersion / 



I have determined the specific heat of the sample of iron cut from the 

 boiler to be 0.113 at a temperature of 212° Ft., and as it is considerably 

 greater at higher temperatures, I have therefore assumed it to average ^ 

 that of water. 



Experiments made with gunpowder to ascertain the rapidity of explo- 

 sion, showed that with various kinds of gunpowder the time required for 

 complete ignition of a thin stratum of powder, spread over a surface equal 

 to the area of the crown-sheet, when ignited at one edge only, varied from 

 one-quarter of a second to one and a half seconds ; and as the destructive 

 effects are most impressive to the popular mind, they serve to illustrate 

 the effects that can be produced by converting water into steam as the 

 increase in volume is about the same, that is, 1700 volumes of vapor are 



