METHOD OP SHORTENING CHEMICAL CALCULATIONS. 
307 
For the following proposition I am indebted to my lecture notes 
taken at Melbourne University : — 
“ If V be the volume of gas under a pressure P at an absolute 
temperature T, then, no matter how the volume, temperature, and 
V P 
pressure be changed, remains a constant.” 
This can be easily proved, for if V 1 be the volume of the same 
gas under a pressure P 1 , and an absolute temperature T 1 , then, if the 
pressure change from P to I Jr while the temperature remains constant 
and v be the resulting volume, by Boyle’s Law, 
y p = v p* (i). 
If, now, the temperature of the volume v change from T to T 1 , 
while the pressure (P r ) remains constant, and V 1 be the resulting 
volume, then, by Charles’ Law, 
v* 
V 
( 2 ). 
and 
Hence, by (1) and (2), 
V x pi _ 
V 1 P 1 
T x 
YPT 1 
T, 
_ YY 
T? 
Thus, 
V P 
T 
has a constant value. 
=62T4. 
I have found that by adapting this result to the calculations in 
question the work is greatly facilitated, and there is less liability to 
error. In the hope, therefore, that this may prove of service to 
others, I submit these no+es. 
2 
ftemembering that -r- — or 22*32 litres of any gas weigh its 
*u»yo, 
molecular weight expressed in grammes, we may work out, once for 
y p 
all, the value - 7 ^— 
y P 22*32 x 760. 
T ” 273 
Hence y = 62*14 x 
Where y is the volume in litres of an amount of any gas which 
weighs its molecular weight when expressed in grammes, when under 
a pressure of P mm. and at an absolute temperature T. 
This result is readily applied, as the following example shows : — 
Suppose that it is required to find what volume of nitrous ox?de 
at 15° C. and 740 mm. is given by 30 grammes of ammonium nitrate. 
Here T = 273 + 15° C. = 288° and P = 740 mm. 
NI1 4 N0 3 = 2H,0 + N a O, 
80 = 36 + 44, 
