800 TRUEBLOOD. 



point of tlie high-side steam does not He on the throttling curve. 

 However, in these as well as in experiments in which the high side 

 steam was really dry, the slope of the tangent to any throttling curve 

 plotted in the (p, T) plane is the value of /x at the point in question, 

 provided, of course, that the throttling has been adiabatic. 



Since the experiments in question were primarily undertaken for 

 the purpose of determining sets of throttling curAes rather than the 

 slopes of these curves, none of the experimenters used differential 

 apparatus in either the drop of pressure or the drop of temperature 

 measurement. Both drops were usually much larger than any in the 

 work of the present writer. Thermometers were not read more 

 closely than 0°.l C. and this place was, as a rule, uncertain. It is 

 therefore to be expected that large accidental errors will appear in 

 values of /x calculated from the work of these three investigators by 

 taking differences between successive low-side pressure and tempera- 

 ture readings obtained with the same high side conditions. Such 

 calculations have been very carefully carried through by Davis in a 

 paper already referred to ^^ and the results are embodied in tables I, 

 II and III and in the figure 6, of that paper. Davis also exhibits in 

 figure 7 of the same paper a curve representing the Joule-Thomson 

 effect for steam as a function of the temperature. This curve is 

 based, not only on the work of Peake, Grindley and Griessmann, but 

 also on steam experiments at other temperatures by Dodge and on a 

 number of experiments on carbon dioxide, it being assumed, with 

 regard to the last-named, that the law of corresponding states holds 

 for the Joule-Thomson effect in carbon dioxide and water. This 

 curve gives about 3°. 11 C. cm.ykgm. as the value of ix for steam at 

 165° C. — about 2.2 per cent, lower than the value (3.182) obtained 

 by the present writer with plug S. 



The influence of the carbon-dioxide points is probabl}' scarcely felt 

 at the temperature in question, as a glance at Davis' figure 6 will 

 show (105° C. = 0.687 reduced, using 365° C\ for the critical tempera- 

 ture of water, as Davis did). However, to avoid any possible effect 

 of this sort, and also to avoid an effect due to the manner in which 

 Davis grouped the results of the throttling experiments in obtaining 

 the coordinates of the points of his figure 6, the values of all Joule- 

 Thomson coefficients given in Davis' tables I, II and III for tempera- 

 tures lying within the interval 0.671 to 0.703 reduced (corresponding 

 to 155° to 175° C. for steam) have been considered directly. There 



19 Proc. Am. Acad., 45, 243-264 (1910). 



