36 THE COMPRESSIBILITY OF CARBON, SILICON, 



CALCULATION OF RESULTS. 



Attention is now directed to the calculation of the correction to be 

 applied for the pressure of the compressible liquid in the jacket around 

 the substance under investigation. This is performed in a manner exactly 

 analogous to that used for the similar correction applied in the case of the 

 alkali metals, except that in the present case water, not paraffin oil, was 

 the supplementary liquid used. 



The compression of water between 100 and 500 pressure-units is, 

 according to our measurements, already summarized above, 0.01642 of its 

 bulk,* or for 1 gram of water at 20, 0.01645 milliliter. The difference 

 between this compression and that of the same bulk of mercury, 0.00148 

 between the same pressures, is 0.01497. As the density of mercury under 

 500 atmospheres pressure at 20 is 13.57, the quantity 13.57 X 0.01497 

 0.2031 gram more of mercury would have to be added to a jacket con- 

 taining a gram of water besides the mercury than to the same jacket filled 

 with mercury alone, over the stated range of 400 pressure-units. When 

 water is the liquid used, these figures, 1 gram and 0.2031 gram, take the 

 place of the values K and W - - W " , respectively, in the equation given 

 under the alkali metals for the calculation of the results. Thus the com- 

 pressibility of a substance is found from the data given below by the 

 following equation when water is used : 



IK)D + 0.00000371 



where W = the weight of mercury added to the jacket containing the 

 solid substance, mercury, and water for 400 units of pres- 

 sure between 100 and 500 units. 

 W = the corresponding weight of mercury, added when mercury 



alone is present. 



K = the weight of water present. 

 D = the density of the substance under investigation. 

 A = the weight of the substance. 

 0.00000371 = the average compressibility of mercury between 100 and 



500 pressure-units. 



As an example the case of selenium may be cited. With 2.075 grams 

 of water and 19.48 grams of selenium of density 4.28 in jacket vn, it was 

 found from the curve that 0.696 gram of added mercury demanded an 

 increase in the contact-pressure from 100 to 500 kg. per square centi- 

 meter. This weight of mercury is W in the equation. W , the similar 



*See p. 33. 



