The Air Density Equation and the Transfer of the Mass Unit.

A new formul a tion of the equation for cal cul ation of a ir dens it y has been developed. The Cohen a nd Taylor va lue of the gas constant, currently accepted values of the atomic weights, and recent determinations of abunda nces of the various co nstituents of air have been used. The abundance of carbon diox ide has been treated as a variable and a fac tor enabling convenient adjustme nt of th e appa rent molec ul a r we ight of air fpr de vi ation of ca rbon dioxide abundance from a background va lue has been derived. A new ta ble of the co mpress ibi li ty facto r for the range of pressure and tempe ra ture of int e rest in s tanda rd s labo ratories has bee n ca lcula ted using recen tl y de te rmin ed va lues of vi ri al coeffi c ients. The enhance ment fac to r, whi ch has usua ll y been ignored , has been ex pli c itl y included . A s imple eq uation for the ca lcul ation of enhancement factor has been fitted to va lues in the ra nge of pressure and temperature of int erest. A s imp le eq ua tion for the ca lcul a tio n of sa tu ra tion wa te r vapo r pressure has been fitted. Uncertainties, random and systematic, in the parameters and in the measurement of environmental variabl es and consequent uncerta inties in ca lcul ated air density have been estim ated. Appli cation of the eq uation to a ir buoyancy dete nnina tion and the transfe r of th e mass unit at th e va,-ious na tio na l stand ard s laboratories has been made.