DAVIS. — THE LAW OF CORRESPONDING STATES. 



247 



to lower low side pressures and temperatures, which when plotted 

 together form the throttling curves of Figure 2. Since it is character- 

 istic of throttling that the total heat, H, of the steam is the same on 

 the high and low sides, it follows that H is constant along the whole 

 of any throttling curve, and that an/ two low side points of a run may 

 be taken, one as describing the high side conditions and the other as 

 describing the low side conditions of a possible throttling experiment. 



Figure 2. Grindley's throttling curves. Abscissae are pressures in lbs. 

 per sq. in. Ordinates are Fahrenheit temperatures. From his paper in the 

 Philosophical Transactions. 



In other words, the slope of a throttling curve at any point is a value 

 of the Joule-Thomson coefficient under corresponding conditions. It 

 is therefore possible, even while rejecting all of Grindley's high side 

 points together with that one of the low side points which is obviously 

 affected by the same error, to use the remaining low side points in 

 pairs. There were 101 of them in all, lying on seven throttling curves. 

 They were first grouped so as to give 29 average points, the averaging 

 being justified by the fact that for a range of not more than 5°, a 

 throttling curve can be considered straight. These means were then 

 taken two by two consecutively to give 22 values of the Joule-Thomson 



