GEOPHYSICAL LABORATORY. 135 



the change in free energy for the reaction under standard conditions. For 

 the reaction Sj^+02<zz>S02 under similar conditions, the value for the change 

 of free energy is —69761. 



These quantities will subsequently be made use of in calculating various 

 equihbria in which sulphur dioxide plays a part. 



(20) The representation of a volcano on an Italian renaissance medal. H. S. Washing- 



ton. Art and Archaeology, 7, 256-263 (1918). 

 This paper describes a lead medal of Leonello Pio, Count of Carpi, which 

 dates from the beginning of the sixteenth century. The reverse represents a 

 volcano in violent eruption, and it is shown that this commemorates almost 

 certainly an eruption of Vesuvius in 1500, concerning the actuaHty of which 

 there has existed considerable doubt. If so, this is the earhest known repre- 

 sentation of Vesuvius in eruption. 



(21) Some points regarding calorimeter efficiency. Walter P. White. J. Franklin Institute, 



186, 279-287 (1918). 



This discussion has special reference to the precision required and the con- 

 ditions prevalent in commercial work. 



The errors directly affecting a calorimeter may be reduced to two sorts: 

 (1) the most important, usually, are those in the principal thermometer 

 readings; (2) the most varied are those in determining the effect of leakage 

 of heat from the calorimeter during the experiment. The principal sources 

 of these errors are: (a) imperfect control of the surrounding temperature; (6) 

 insufficient stirring in the calorimeter; (c) irregular heat production from 

 irregular speed of stirring; (d) evaporation; (e) lagging temperatures. The 

 last are usually negligible in commercial work, and the other errors can be 

 made so. In the very similar determinations of commercial work these small 

 errors tend to cancel out between cahbration and final measurement, and 

 thereby certain short methods become possible. In the main, these make for 

 convenience, while precision depends mostly on the thermometer and more 

 on control and definiteness of such things as jacket temperature than on 

 special methods. The adiabatic method does not improve the situation 

 regarding errors a, h, and c; and error d can be otherwise managed. This 

 method is probably less valuable in commercial work than elsewhere. A 

 mere glass-jacketed vessel is not rightly called adiabatic; it has a leakage-rate 

 as much as one-third or one-fourth that of an ordinaiy calorimeter . 



(22) Note on a universal switch for delicate potential measurements. Walter P. White. 



Am. J. Sci., 46, 610-612 (1918). 

 This paper describes two improvements found to be desirable after trial 

 of the switch described in 1916 ("A universal switch for thermo-element work 

 and other potential measurements," reviewed on page 146, Year Book No. 15). 



(23) The specific heat of platinum at high temperatures. Walter P. Wliite. Phys. Rev., 



12, 436-441 (1918). 

 The specific heat of platinum has been redetermined from 100° to 1300° 

 with a precision estimated to be better than 0.3 per mille and with very satis- 

 factory agreement with the results of Gaede at 100° and with those of Plato, 

 Corbino, Magnus, and Fabaro at higher temperatures. Most pubHshed re- 

 sults below 100° appear to be 1 per cent or more too high. The atomic heat 

 of platinum at constant volume is, from 100° up, above the value 5.96, indi- 

 cated by Dulong and Petit's law and by the accepted kinetic theories of the 

 sohd state, and also increases regularly to 1300° and probably beyond that. 



(24) Description of the quantitative classification of igneous rocks. Henry S. Washington. 



Extract from Professional Paper 99, U. S. Geological Survey (1918). 



This is a reprint of the appendices to Professional Paper 99 (pp. 1151-1185) 

 (reviewed under Abstract No. 11 of this report), embodjdng a description of 



