122 
DE. ATs^DEEWS AJSD PEOFESSOE TAIT ON THE 
temperature. Let also ge=fd=x, and let H be the length of a tube similar to the 
siphon tube, and whose capacity is equal to that of the resen^oir and of the siphon tube 
to f. Let a be the height of a barometer containing the liquid in the siphon tube, ^ 
the pressure of the gas in the vessel, and V the volume of the gas reduced to 0° C. and 
760 millims. 
Then, evidently, y l+«^ 
^ U+x 
But 
hence 
v(i+«0 
n(H+*)(i+f) 
is a constant quantity. Taking the logarithmic differential, we have 
8V . uBt Sn 8a? 
o=- 
\ + ut n H+a? 
28a? 2a?8a 
a c? 
^ 2a? 
1 -1 
a 
X 
Now ~=^ is multiplied by a quantity rarely exceeding To this degree of 
approximation, then, at least, 
8V , alt 8n__^ /2 , 1\ , 
v+i+a# 
If Vp Hp x^ represent for the auxiliary vessel the quantities corresponding to V, H, x 
in the primary, we have, since SV,= 0, 
alt 8n . /2 , 1 \ 
rnr-ir=^^-(s+H,j- 
( 2 .) 
If H^=H, e. if the primary and auxiliary vessels be of similar dimensions, we have at 
once, from (1.) and (2.), 
(3.) 
If the vessels be not similar, let 
then instead of (3.) we have 
?|=(S*-S*„)(?+i) (4.) 
Formula (3.) or (4.) gives the change of volume in the gas, as deduced ffom the observed 
change in the levels in the siphon tube. 
For the estimation of the portion of the gas (^,V) taken up as ozone by the solution 
of iodide of potassium, let C be the capacity of the primary vessel toy'in litres, s the 
number of measures of sulphurous acid required to decolorize the solution when washed 
out of the vessel, S the number required to decolorize 1 grm. of iodine. Then we have, 
