552 
DR. A. SCOTT ON THE COMPOSITION OF WATER BY VOLUME. 
The impurity was called 0 when the impurity was less than '1 = about of a 
cubic centimetre, or = TcnrUoo of volume of the gases used. 
The gases were measured moist, and the surface of the measuring vessel was kept 
thorouglily moist by washing the apparatus with distilled water in the evening and 
expelling the water, and then leaving it full of mercury and expelling what had risen 
through the night, so that no appreciable error was introduced from water present as 
such in the vessel. One advantage of working with moist gases and vessels with 
moist surfaces is that the gases can be so completely got rid of, none remaining as a 
film. When both manometer and measuring vessel were completely filled with 
mercury and the reservoir lowered so as to produce a Torricellian vacuum in both, it 
was usual for the mercury to remain for some time 300 to 400 millims. higher in the 
measuring vessel than in the manometer, the mercury not leaving the moist glass till 
a trace of gas from the stopcock 2 set it off. 
The following experiments taken at random show the modes of measurement and 
calculation adopted. 
August 24th, 1889. Experiment XXXIV., Series If. Apparatus with Variable 
Volume. 
Oxygen from mercuric oxide— 
Volume 50'0 = 3881'0. Temperature == 15'4° C. 
millims. millims. 
Height of mercury in manometer tube on scale = 71’3 on cathetometer = lO'O 
,, ,, volume tube on scale . = 71’6 ,, —■ 10‘3 
Correction.= — 0*3 = — O'o 
millims. 
Barometer 777d — 2G‘0.=:=75L1' 
Pressure of aqueous vapour . . . . = 13‘0 
.•. Pressure of oxygen = 751T — ’3 — 13'0 . . = 737'8 
Hydrogen from electrolysis of dilute hydrochloric acid— 
Volume 45'3 = 3819’6. Temperature = 15’35° C. 
millims. 
Height of mercury in manometer tube on scale . . . . 118'5 
,, ,, volume tube on scale. 118'5 
Correction.= ’0 
Barometer 777-4 - 25-8 .= 751-G 
Pressure of aqueous vapour.= 13-0 
.-. Pressure of hydrog;en = 751-0 — 13-0 .= 738-6 
