ON THE MECHANICAL EQUIVALENT OF HEAT 399 



ity at the boiling point? And of all the bodies which we should select as 

 probably exhibiting this property, water is certainly the first. 



(&.) Heat Capacity of Calorimeter 



During the construction of the calorimeter, pieces of all the material 

 were saved in order to obtain the specific heat. The calorimeter which 

 Joule used was put together with screws, and with little or no solder. 

 But in my calorimeter it was necessary to use solder, as it was of a much 

 more complicated pattern. The total capacity of the solder used was 

 only about -$fa of the total capacity including the water; and if we 

 should neglect the whole, and call it copper, the error would be only 

 about y-gVfr- Hence it was considered sufficient to weigh the solder 

 before and after use, being careful to weigh the scraps. The error in 

 the weight of solder could not possibly have been as great as ten per 

 cent, which would affect the capacity only 1 part in 12,000. 



To determine the nickel used in plating, the calorimeter was weighed 

 before and after plating; but it weighed less after than before, owing 

 to the polishing of the copper. But I estimated the amount from the 

 thickness of a loose portion of the plating. I thus found the approxi- 

 mate weight of nickel, but as it was so small, I counted it as copper. 

 The following are the constituents of the calorimeter: 



Thick sheet copper 25-1 per cent. 



Thin sheet copper 45-7 " 



Cast brass 17-9 " 



Boiled or drawn brass 5-7 " 



Solder 4-0 



Steel 1-6 " 



100-0 

 Mckel -3 " 



To determine the mean specific heat, the basket of a Regnault's 

 apparatus was filled with the scraps in the above proportion, allowing 

 the basket of brass gauze, which was very light, to count toward the 

 drawn brass. The specific heat was then determined between 20 and 

 100, and between about 10 and 40. Between 20 and 100 the 

 ordinary steam apparatus was used, but between 10 and 40 a special 

 apparatus filled with water was used, the water being around the tube 

 containing the basket, in the same manner as the steam is in the 



