NOTES AND COOLIDGE. — ELECTRICAL CONDUCTIVITY. 191 



a maximum error, even at 300°, of only 0.05 per cent in the specific 

 volume. 



2. The quartz-crystal cup expands upon heating, thus diminishing the 

 volume of the bomb occupied by the solution. The correction for this, 

 even at 306°, amounts to only —0.03 per cent. 



3. The bomb expands owing to the pressure within. At 306°, where 

 this correction is greatest, the vapor pressure plus the air pressure may 

 be estimated at 100 atmospheres. Assuming that the modulus of elas- 

 ticity of the steel is 17372 kgm. per sqmm., which is the value found by 

 Pisato* at 300°, the volume correction due to this cause is +0.025 per 

 cent. This is opposite in sign and essentially equal to the preceding 

 correction : they therefore eliminate each other. 



4. The volume of the tube Ti is only 0.07 ccm. or 0.06 per cent of the 

 whole volume of the bomb. It is therefore so small that no irregularities 

 in the extent to which it is filled with solution could much affect the result. 



5. The volume of the bomb depends somewhat on the extent to which 

 the large nut is tightened up and the gold packing-ring compressed. Four 

 of the cold rinws which had been used were chosen at random, and the 

 mean thickness of each was calculated from measurements made at eight 

 equidistant points with a micrometer caliper. The average deviation 

 from the mean thickness of these rings was such as to affect the volume 

 of the bomb by only 0.02 per cent. So this source of error can be un- 

 hesitatingly disregarded, especially as each final specific-volume value is 

 the mean of the values obtained from several independent runs. 



6. The bomb is never completely filled with liquid, the vapor space 

 amounting, on an average, to about 1 ccm. or 0.8 per cent of the total 

 volume of the bomb (about 124 ccm.). A certain fraction of the water 

 is therefore vaporized, and the specific volume appears too small by a 

 corresponding amount. The specific volume of the vapor is not yet 

 known above 200°. By extrapolation, however, from the values up to 

 200°, the specific volume of the vapor at 218° is found to be seventy- 

 five times that of the liquid. From this it follows that at 218° the 

 correction is only y^ X y^' <^^ about 0.01 per cent. 



Such a calculation is not possible at the higher temperatures, 281° 

 and 306° ; but that no considerable error arises from this source was 

 shown by direct experiments. Namely, when two or more specific-vol- 

 ume determinations were made, the amount of solution taken in the dif- 

 ferent experiments was purposely varied, so that the vapor space should 



* Nuovo Cimento (3), 4, 152 (1878). 



