386 VAPOR-DENSITIES. 



gives a reduction of density from 2*65 to 2*28, which is about one- 

 ninth less. This is, it will be observed, a deviation from the formula 

 in the opposite direction from that which the experiments of Naumann 

 alone, or a comparison of the experiments of Troost with those of 

 Deville and Troost, seemed to indicate. The experiment here com- 

 pared with Naumann's belongs to the III d series of Deville and Troost. 

 If instead of this experiment we should take an average of the 

 experiments at lowest temperature in the II d and III d series, the 

 agreement with the formula with respect to the effect of change of 

 pressure would be almost perfect. 



Formic acid. In Table III, the determinations of Bineau are 

 compared with the densities calculated by the formula 



1-589 (D- 1-589) 3800 

 lQ g (8178-Dy = MT273 +1 ^- 12 ' 64L (11) 



The observed densities are taken from the eighteenth volume of 

 the third series of the Annales de Chimie et de Physique (1846), 

 except in three cases, distinguished by parentheses, which are earlier 

 determinations published in the nineteenth volume of the Comptes 

 Rendus (1844). It may be added that the pressure (687) for the 

 experiment at 108 is taken from Erdmann's Journal fur praktische 

 Chemie (vol. xl, p. 44), the impression being imperfect in the Annales, 

 in the copies to which the writer has been able to refer, where the 

 figures look much like 637. (The pressure 637 would make the 

 calculated density 2*28.) 



In the column which gives the excess of observed densities, the 

 effect of nearness to the state of saturation is often very marked. 

 Such cases are distinguished by an asterisk. The temperature of 

 99*5 is below the boiling point of formic acid, and the higher 

 pressures employed at this temperature cannot be far from the 

 pressure of saturated vapor. With respect to lower temperatures, 

 we have the statement of Bineau that the pressure of saturated 

 vapor is about 19 mm at 13, 20'5 mm at 15, 33'5 mm at 22, and 53'5 mm 

 at 32. By interpolation between the logarithms of these pressures 

 (in a single case, by extrapolation), we obtain the following result : 



Temperature, - 10 '5 12 '5 16 18 '5 22 



Pressure of sat. vapor, - 16 "6 18 '5 22 26 '2 33 "5 



Pressure of experiment, - 14 '69 15 '20 15 '97 23 '53 25 '17 



