353 



the bnfane was not absolutely pure. It seemed therefore preferable 

 to treat the theoretical normal volume as an unknown quantity and 

 deduce it together with the other contants from the observations. 

 It was for' this purpose, that the above weighings at 0' at three 

 different pressures were made. 



Substituting in [2) p^, v^ and p^, v^ respectively and dividing the 

 two resulting equations, we obtain the relation 



p,v, B B- \ f G\ ] 



In this equation we may take for v^ and v^ the volumes of 

 1 gramme in ccm. The term containing C is of minor importance: 

 C may therefore be calculated with sufficient accuracy from the 

 reduced coefficient ^, which is known from measurements on a 

 number of other substances. 



From equation (3) was found 5 = — .0430. 



In the same manner the second and sixth weighings gave 

 B ^ — .0431 ; as the mean was taken .0431 . 



The theoretical normal volume of the butane used may now be 

 calculated from equation (2): it becomes 388.1. 



The difterence of this figure from the value for pure butane 

 (386.0) gives an indication as to the amount of the impurity : it points 

 to the presence of a lighter admixture. The difference is .57o- 



Using the normal volume found in this manner we may now 

 deduce the virial coefficients B in the measurements at other 



In the last column are given the values of B, as calculated from 

 the mean reduced virial coefficient ^ for a number of substances. 

 The correspondence is satisfactory considered the degree of accuracy 

 of the method by which B was here determined. An error in the 

 fraction on the left side of equation (3) appears in B one hundred 

 times enlarged ; an error of S"/,, in B corresponds to an error of 

 observation of V^ooo- 



Moreover a complete correspondence can in any case not be 

 expocled, as the equation of sfate is after all only an a;)proxiinali()n 



23 



Proceedings Royal Acad. Amsleidam. Vcl. XVI. 



