ON EVAPORATION AND DISSOCIATION. 
81 
§21. Pressures of Dissociation of Butyl-chloral hydrate in Barometer-tube. 
Temperature. 
Pressure. 
Time required for equilibrium. 
O 
millims. 
15-0 
5'8 
2 hours 
35-0 
231 
81' 
16-0 
9-5 
Stood all night. 
35-0 
25-9 
51' 
50-0 
49-5 
52' 
60-0 
86-0 
95' 
70-0 
1897 
73' 
77-8 
307-0 
28' 
85-0 
428-0 
7' 
90-0 
569-7 
2' 
Tire curve is represented in Plate 1. 
§ 22. Temperatures of Volatilization of Butyl-chloral Hydrate. 
The thermometer-bulb was coated as usual, and the still was jacketed with aniline 
vapour. The initial pressure was 2*15 millims. The temperature rose gradually to 
68*5°, and then fell again to 66*5°; the pressure falling to 2*0 millims. The pressure 
was then raised to 6*8 millims. ; the temperature continued to fall very slowly to 66°. 
On raising pressure to 15*2 milli m s., temperature fell to 65*5° ; and with a pressure of 
28*5 millims. temperature remained constant. When pressure was raised to 52*7 
millims. temperature rose to 66°; pressure was increased to 65'9 millims., when tem¬ 
perature rose gradually to 6 9'7°, when the substance in contact with the stem of the 
thermometer became moist. On reducing pressure to 21*8 millims. solidification 
immediately ensued; but as the substance had largely evaporated, readings of 
temperature were doubtful. 
A second series of experiments was made. The initial pressure was 1*9 millims., 
the temperature rising to about 63°. On raising pressure to 3*8 millims., no alteration 
in temperature was noticed. At 26‘1 millims. temperature rose slowly to 64*5°. 
Pressure was then reduced to 13*9 millims., and the temperature fell to 63°. The 
reduction of pressure was continued until it reached 2’8 millims. ; the temperature 
fell to 62'5° when the pressure was 5*5 millims., and gradually rose again to 64°. 
Pressure was then raised to 48 millims., and temperature rose to 68°. With rise of 
pressure to 65’2 millims., temperature rose to 69’2°, and the upper portion of the 
substance melted. On reducing pressure to 22 millims. solidification occurred, and 
temperature fell to 65-4°. 
§ 23. It will be seen that these results are most erratic ; but it is to be noted that 
the total range of temperature was only from 62‘5° to 69'2°, while the pressure varied 
from 1*9 millims. to 65‘9 millims. The only conclusion to be drawn is that temperature 
and pressure are independent of each other. 
MDCCCLXX XVI. M 
