156 Mr. Carl Barus on the Pressure-Variations of 



a fusing-point method, give 1450° as the maximum tempera- 

 ture for boiling bismuth, which means, however, that it is 

 short of the melting-point of nickel taken at 1600° (Van der 

 Wyde). In my own experiments * with a Fletcher furnace 

 like fig. 2, I signally failed to boil bismuth f in a number of 

 trials, in which I used three blast-burners. The boiling- 

 point criterion in the present results is beautifully exhibited. 

 When pressure increases, the group of points B on the chart 

 passes into group A ; hence the group B are boiling-points. 

 When pressure increases further, the group A do not 

 increase in temperature ; hence the group A are not boiling- 

 points {. The zinc and the later sulphur results are most 

 satisfactory. Irregularities in the cadmium observation for 

 the higher pressures I attribute to leakage of the crucible 



The straight lines running obliquely across the chart 

 exhibit the approximate truth of Groshans's principle. The 

 abscissae are boiling-points, 6, at 76 cm., the ordinates boiling- 

 points at 76 cm. and 4 cm. respectively, all expressed in double 

 absolute degrees Centigrade ; i. e. the chart shows the varia- 

 tions of 6/2. Mercury and sulphur fall below the line of 

 proportionality. Inasmuch as it is possible that the 4 centi- 

 metre data for zinc and cadmium are slightly superheated, the 

 general agreement of data may be better than it here appears. 

 It is by aid of this diagram that the bismuth constants in 

 Table VIII. were computed. 



16. Bertrand computes the constants of Dupre's formula 

 for 16 substances, and shows its admirable agreement with 

 observed data throughout. The constants in such a summary 

 vary largely : A between 4 and 21 (pressures being expressed 

 in centimetres of mercury); C between —9 and +5. In 

 any such grouping of constants as I have very roughly 

 attempted, the agreement of the formula with facts would 

 therefore be lost. It is worthy of remark, however, that in 

 10 of the 16 substances, A lies between 15 and 21*5, and in 

 one half of the substances C lies between 3*2 and 4*2. 



When, however, the errors left in any attempt to group 

 the constants are considered, not so much with reference to 

 the small range of temperatures of a single substance, but 

 rather with regard to the relatively large range of tempera- 



* Bull. U.S. G. S. no. 54, pp. 116-118, 124. 



t In determining the vapour-density of bismuth, Biltz and V. Meyer 

 heat bismuth up to 1700° (Chem. Ber. xxii. p. 725, 1889), but the tem- 

 perature is purposely chosen high. 



\ Very interesting experiments on the volatilization of metals in vacuo 

 and at low temperatures (Cd at 160°, Zn at 184°, Sb and Hi at 292°, Pb 

 and Sn at 360°) are due to Pemarcay, C. JR. xev. p. 183, 1882, 



