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LIV.—APPROXIMATE FORMULA FOR THE VOLUMES AND 
WEIGHTS OF GASES, sy G. JOHNSTONE STONEY, D.Sc., 
F.R.S., SECRETARY TO THE SOCIETY. 
[Read March 15th, 1880.} 
Turse formule are founded on the circumstance that at a tem- 
perature of 21° C. and pressure of 760" one gramme of 
Hydrogen, 16 grammes of Oxygen, and 14 grammes of Nitrogen 
occupy very nearly 12 litres. The outstanding differences are of 
the same small order as the degrees in which these gases fall 
short of obeying accurately Boyle and Charles's laws. And in 
general, at the above quoted temperature and pressure, D gram- 
mes of any sufficiently perfect gas will occupy nearly 12 litres, D 
being the density of the gas referred to Hydrogen. 
Hence we get the exceedingly simple formulee that 
D 
and 
ialZe 
7D 
where G is the number of grammes weight of the gas present, and 
Lthe number of litres it occupies at 21° C., and 760™ pressure. 
These formulze will suffice when the barometer stands at 760": 
and when the temperature of the laboratory is 21°. At other 
temperatures and pressures the correction to be applied is one 
per cent. added to G or taken off from L for every 3° that the 
temperature is below 21°, and an equal correction, @.¢. a correction 
of one per cent. added to G or taken off from L for every 73" that 
the barometer stands above 760™™ 
With these simple corrections the formule are sufficient for all 
ordinary practical purposes, at atmospheric pressures, and between 
the temperatures of -— 5° and + 30°; the maximum error with 
Oxygen nowhere between these limits exceeding ‘005 of the 
whole amount, that with Hydrogen or Nitrogen not exceeding 
003. It follows, of course, that with any other nearly perfect 
gas, the error is of a similar negligible amount. 
