THE ATOMIC-WEIGHT LAW. 



179 



cates. Hence, the selection of KN0 3 (max. at 7.1 /) from the nitrates by 

 Morse seems arbitrary, for Pfund (loc. cit., see Carnegie Publication No. 

 65) has given a large number of nitrates which have a band in common at 

 7.45 11. This seems to be a characteristic band of the nitrates, and AgNO s 

 might have been selected instead of KN0 3 . A characteristic band of the 

 sulphates appears to be at 9.1 il (harmonic with the one at 4.55 li), while 

 Morse selected a less frequent one at 8.6 li. From the silicates, MgSi0 3 , 

 with an insignificant band at 9.1 /<, was selected, while Na 2 Si0 3 , with a 

 sharper band at 9.9 li, and Zn 2 Si0 4 , with a group of still more intense 

 bands at 10.1, 10.6, and 11 li, respectively, were not considered. 



In PbM0 4 the maxima lie in the region of 11.75 an< ^ 1 3 /*> while in 

 CaW0 4 there is a large reflection band with maxima at about 11.4, 11.9, 

 and 12.5/*, respectively. These data including Morse's are plotted in 

 fig. 106 and tabulated in table XI, from which it will be observed that 



Table XI. 



the graph is not a straight line, and that if any relation exists it is a very 

 complex curve, showing that for the region up to 10 /x the atomic weight 

 of the element in the acid radical has a great effect in shifting the maxi- 

 mum, while beyond this point the atomic weight of the element united 

 with oxygen is of minor importance. In fact, the base and the element 

 united with the oxygen in the acid radical seem to influence each other. 

 As an illustration of the arbitrariness in selecting bands to establish 

 relations like the aforesaid, calcite (CaC0 3 ) may be noticed, in which the 

 reflection band is complex with maxima at 6.4 (?), 6.5, 6.6, and 7 ll, while 

 in its isomer, aragonite, the maxima are at 6.4 (?), 6.52, 6.74, and 7 (?)/<. 

 In SrC0 3 the band with a maximum at 6.67 jx could not be resolved even 

 with a fluorite prism. Hence, one is at a loss to know which band (at 

 6 to 7 /i) to select from the carbonates to compare with the sulphates, 

 nitrates, and silicates. On the other hand, in the carbonates and in the 

 sulphates the maxima of the bands have been plotted in their order of 

 occurrence, which would seem to eliminate personal bias in the selection 

 of maxima. From this it would appear that the simple, linear relation 

 between the atomic weight of the base and the maxima of the reflection 



