THERMAL CONDUCTIVITY AND SPECIFIC HEAT OF MANGANESE-STEEL. 953 



to the extreme desirability of a thorough examination of the thermal conductivity of 

 alloys, especially of those whose properties differ in a marked way from those of their 

 components. 



Specific Heat of Manganese- Steel. 



The method employed to determine the specific heat of manganese-steel was practi- 

 cally that known as the "method of cooling"; one which is based on the fact that two 

 bodies, whose surfaces are exactly similar in nature and extent, lose by radiation equal 

 quantities of heat, when their excesses of temperature over that of surrounding bodies 

 are equal. That their losses of heat, under such circumstances, due to the combined 

 effects of radiation and convection, should be equal, it is necessary that the mode in 

 which the two experiments are performed should be as nearly similar as possible; the 

 same precautions as to air-currents, and other influences tending to alter convection 

 effect, should be adopted to the same degree in both. This was scrupulously attended to 

 in the experiments, of which the following details may be given. 



Two cubical masses, one of wrought iron, the other of manganese-steel, were obtained, 

 the latter being a part of the same material as that out of which the bars for the con- 

 duction experiments were made. They were made as exactly as possible of the same 

 dimensions, the length of each edge being If inch. A circular hole, 1 inch in depth, 

 ^-| inch in diameter, was drilled in each ; the axis of the hole being perpendicular to, and 

 in the centre of, one of the faces of the cube. The surfaces of both cubes were made 

 the same by the deposition on them of soot from the smoky flame of a paraffin lamp. 

 One of the cubes was raised to a convenient temperature, say 300° C, by the flame of a 

 Bunsen burner, and then allowed to cool, its temperature being noted at intervals by a 

 thermometer whose bulb was inserted into the hole, which was filled up with a few drops 

 of mercury to ensure good thermal contact of the bulb with the sides of the hole. The 

 other cube was meanwhile placed at a distance, and used, by its thermometric indications, 

 as a means of ascertaining the temperature of surrounding bodies. The thermometer 

 employed for these cooling experiments was that used in the cooling experiments on the 

 short bar in the conduction investigations ; its error was well known by comparison with 

 carefully- constructed Kew standards. 



By such means the rates of cooling of both cubes were deduced from the observations, 

 throughout a considerable range of temperature excess. Then, if m, m be the masses 

 of the iron, and manganese-steel cubes, respectively ; c, c, their specific heats ; r, r , their 

 rates of cooling at the same given temperature excess, 



m r'c = mrc, 



since each of these quantities represents the amount of heat lost in unit time at the 



given temperature excess. Hence 



, mr 



c = — —, c . 

 mr 



Thus, if the specific heat of iron be known throughout the range of temperature used, 



