402 



HENRY A. EOWLAND 



meter, the time being indicated by the horizontal line. Continue the 

 line d c until it meets the line I a. Draw a horizontal line through 

 the point I. At any point, &, of the curve, draw a tangent and also a 

 vertical line bg; the distance eg will be nearly the value of the con- 

 stant c in the formula?. Lay off I f equal to c, and draw the line fJiTc 

 through the point h, which indicates the temperature of the atmos- 

 phere or of the vessel surrounding the calorimeter. Draw a vertical 

 line, j Ic, through the point Tc. From the point of maximum, c, draw 

 a line, j c, parallel to d m, and where it meets Ic j will be the required 

 point, and will give the value of 6". Hence, the rise of temperature, 

 corrected for all errors, will be Ic j. 



This method, of course, only applies to cases where the final tem- 

 perature of the calorimeter is greater than that of the air; otherwise 

 there will be no maximum. 



FIG. 5. 



In practice, the line d m is not straight, but becomes more and more 

 nearly parallel to the base line. This is partly due to the constant 

 decrease of the difference of temperature between the calorimeter and 

 the air, but is too great for that to account for it. I have traced it to 

 the thin metal jacket surrounding the calorimeter, and I must condemn, 

 in 'the strongest possible manner, all such arrangements of calorimeters 

 as have such a thin metal jacket around them. The jacket is of an 

 uncertain temperature, between that of the calorimeter and the air. 

 When the calorimeter changes in temperature, the jacket follows it but 

 only after some time; hence, the heat lost in radiation is uncertain. 

 The true method is to have a water jacket of constant temperature, and 

 then the rate of decrease of temperature will be nearly constant for a 

 long time. 



The following results have been obtained by Mr. Jacques, Fellow of 

 the University, though the first was obtained by myself. Corrections 

 were, of course, made for the amount of thermometer stem in the air. 



