DAVIS. — THE LAW OF CORRESPONDING STATES. 245 



three gases show such discrepancies among themselves as to make un- 

 certain any judgment as to their agreement with each other. What 

 evidence there is, is in favor of the validity of the law of corresponding 

 states ; but an accurate verification of it, especially for two substances 

 with very different critical temperatures, would put the whole subject 

 on a much more satisfactory basis. 



In this paper it will be shown that this law is verified for carbon 

 dioxide and water within the limit of error of the available observa- 

 tions on water. This limit of error is unfortunately quite as great as 

 that of the oxygen, nitrogen and air observations plotted in Figure 1. 

 Nevertheless, a multiplication of evidence, even of an inferior sort, is 

 often valuable, and in this case there is an added interest because, if 

 water, which is known to be anomalous in many ways through associa- 

 tion, is found to obey the law of corresponding states as to its Joule- 

 Thomson effect, it is probable that the permanent gases will also obey 

 that law. 



There are four sets of experiments on water which can be used. They 

 were all undertaken for the purpose of determining the variation of 

 the specific heat of superheated steam with pressure and temperature, 

 an investigation which has since been more satisfactorily accomplished 

 in other ways. Of the four observers, Griessmann 1 used a porous 

 plug very much like that of Joule and Thomson, while the other three, 

 Grindley, 2 Peake 3 and Dodge, 4 used what engineers call a throttling 

 or wiredrawing calorimeter. The essential part of this instrument is a 

 small orifice through which the steam flows tumultuously from one 

 chamber into another, the high velocity of the steam being subse- 

 quently destroyed by friction at the surfaces of the walls of the second 

 chamber and within the steam itself. During this process the kinetic 

 energy of the steam is transformed into heat, all of which, if the 

 thermal insulation is perfect, goes back into the steam. If this trans- 

 formation is complete, the throttling calorimeter is exactly equivalent 

 to a porous plug. To ensure this completeness, one of the three ob- 

 servers (Peake) put a quantity of wire gauze in the path of the 

 steam from the orifice, and another (Dodge) used at times four small 

 orifices instead of one larger one without noticeable change in the 

 results. Grindley took no especial precautions of this sort, but the 



1 Zeitsch. Ver. d. Ing., 1903, 47, 1852 and 1880; also Forschungsarb., Ver. 

 Ing., 1904, 13, 1. 



2 Phil. Trans., 1900-1, 194A, 1. 



3 Proc. Roy. Soc, 1905, A, 76, 185. 



* Jour. Am. Soc. Mech. Engs., 1907, 28, 1265; and 1908, 30, 1227. 



