534 Mixter — ThermocJiemistry and the Periodic Law. 



The study of the irregularities in heat equivalents is limited 

 with few exceptions to oxides, as complete data are lacking 

 for other compounds. Considerations are limited as before to 

 subgroups falling in series 3 to S, where all of the subgroups, 

 in which the heat equivalent of the middle member is con- 

 siderably less than the linear value, are in the odd series 3, 5 

 and 7. The possible exception in case of zirconium, which is in 

 the even series, will be noticed later. Table VI contains the 

 heats of formation with calculated linear values in brackets 

 and the differences between them and the experimental values. 



In four subgroups in series 3, 5 and 7 the heat of oxidation 

 of the middle member falls below the linear value the same 

 amount for each atom of oxygen combined, or about IT large 

 calories. The same difference appears in the heats of the 

 reactions Zn + S and ZnO + S0 3 , but is less for KBr 4- 30. 

 Data needed to complete the study in series 3, 5, and 7 are 

 lacking for gallium, indium and germanium and an element to 

 follow molybdenum is wanting. The heats of oxidation of 

 titanium, zirconium and cerium are irregular, as shown by the 

 following : 



Ti + 20 



Zr + 20 



Ce + 20 



218-4 



177'5 [221-5] 



224-6 Cal. 



The heat of formation of ZrO„ falls below the linear value 

 44 cal. or 22 Cal. for one atom of oxygen. This is a larger 

 difference than found in other subgroups. Moreover, the three 

 elements fall in the even series where the heat values are 

 linear. Hence it appears probable that there are considerable 

 errors in some of the values for the three dioxides. 



The conclusion drawn from the study of the thermochemis- 

 try of the series 3 to 8 is this. The heat equivalents of the 

 elements of a subgroup are either linear functions of the atomic 

 weights, or the heat of formation of the oxide of the middle 

 member falls below the linear value by a constant amount for 

 each atom of oxygen combined. 



It is desirable that new investigations be made of the small 

 groups, as already suggested, and also determinations of the 

 heat equivalents which are not known of the rare elements. 



New Haven, Conn. 



