DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 



275 



mining a straight line as the graph of dH/dt against t. The total heat 

 curve itself can therefore be represented in the range between 100° and 

 190° by an equation of the second degree in t, within the limit of error 

 of the available data. The form selected is 



H = ff 1Q0 + a(t- 100) — b(t— 100) 2 . 



The eighteen means, reduced to a common but still arbitrary zero, were 



50 



100 



Figure 6. dH/dt plotted against t. 

 authorities as in Figure 5. 



150 t 200 



The symbols refer to the same 



used to give a least squares determination of the constants i/ioo, ct and 

 b and of their probable errors, with the following results ; 



ff 100 = arbitrary ± 0.03, 

 a = 0.8745 ± 0.0014, 

 b = 0.000990 ± 0.000020. 



The agreement of the eighteen individual means with this formula is 

 shown in the upper part of Figure 5, the curve being drawn to represent 

 the formula as accurately as possible. It is also shown by the smallness 

 of the three probable errors. Even if these errors are combined in the 

 most unfavorable way, the change in the computed value of H at 200°C. 

 is only 0.37 calories, or about one eighteenth of one per cent of H itself; 

 at lower temperatures the change would be still less. 



