Notices respecting JSew Books. 



349 



and Naphthalene by H. 0. Dickinson. The object of these deter- 

 minations is to provide standard values to aid in the calibration 

 of the various forms of bomb calorimeters in use in commercial 

 laboratories as well as by scientific investigators. The following 

 table shows the degree of agreement with other recent observers. 

 The results are expressed in 15° calories. 



Authority. 



Naphthalene. 



Benzoic acid. 



Sucrose. 



Fries (1910) 



9633 

 9643 

 9631 

 9612 



6318 

 6323 



6323 



3952 

 3945 



Wrede (1910) 



Eoth (1910) 



Laroux (1910) 



Dickinson (1910-1912)... 



In the same number appears a paper by D. R. Harper on the 

 specific heat of copper in the interval 0° to 50°, with a note on 



to 



vacuum-jacketed calorimeters. The value obtained (correct 



third significant figure with temperature coefficient correct to 



10 per cent.) is 



i o u 1 e s 

 c=0-383 4 4-0-00020(2- 25)^ — , 



or c=0'0917 + 0-000048(£-25) 



gr. ae^ 

 cal.„ 



;r. deg. 



In the May number appears an investigation on the insulating 

 properties of dielectrics, dealing with the volume resistivity and 

 surface leakage of a number of insulating materials with the view 

 of ascertaining their suitability for replacing hard rubber. The 

 volume resistivity (iu ohm-centimetres) is over 5000x10'" for 

 special paraffin, ceresin, and fused quartz ; it is about 1000 x 10 15 

 for hard rubber. Mica comes next with a value 200 x 10 15 , and 

 then sulphur with a value 100xl0 i5 . The most insulating 

 variety of bakelite has a value of only 20 x 10 15 , while many 

 varieties of bakelite lie very low (e. g. JNo. 140, 20xl0 6 ). A 

 large number of determinations are made on surface resistivity 

 as affected by light and moisture. These are represented by 

 curves. This is due to a surface film, usually of water or oil, on 

 the insulator, and is generally the important factor in determining 

 the leakage between two conductors. However, for insulators 

 having a vol. resistivity less than 10 4 ohm cms. placed in an 

 atmosphere having a humidity less than 25 per cent., the greater 

 part of the current may flow through the insulator. 



The same number contains a determination by "W. W. Coblentz 

 of the absorption, reflexion, and dispersion constants of quartz, 

 an accurate knowledge of which is so necessary in order to 

 determine spectral energy curves of a black body when a quartz 

 prism is used. Data are given extending from the ultra-violet to 



