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Liquid Nitrogen

Cailletet first liquefied nitrogen by compressing it to 200 atmospheres and allowing it to expand rapidly. Liquid nitrogen is colourless, with a refractive index of 1.2053. The critical data of nitrogen, according to different investigators, is given in the following table:

Critical temperature: from -147.13 to -144.7
Critical pressure: from 33.49 to 35.00
Critical density: from 0.31096 to 0.32690

The following table gives the variation of the boiling-point of nitrogen with the pressure:

Variation of the boiling-point of nitrogen with the pressure

Pressure, mm. (Cath.)Absolute Boiling- point.Pressure, Atm. (Crommelin.)Absolute Boiling- point.
120.964.512.50786.21
361.671.547.37099.51
561.374.8321.82117.62
76077.3133.46 crit. pt.125.96
938.679.18
1591.184.21


The empirical formula, giving the vapour pressures of liquid nitrogen at any temperature between -208.36 to -148.08° C., maybe written as:

log p = -510.64/T + 12.381 - 0.12696T + 0.0008302T2 - 0.0000019975T3, where T=t+273.09.

Densities of liquid nitrogen at various temperature

t° C.Density of Liquid.Density of Gas.
-148.080.43140.18620
-149.750.47990.16380
-153.650.53320.11170
-161.200.60710.06987
-173.730.69220.02962
-182.510.74330.01558
-195.090.80430.00490
-200.030.82650.00278
-205.450.84990.00136
-208.360.86220.00089


These values may be compared with those of earlier investigators and with others, from which the following densities (of liquids only) have been selected:

t
-210.5-205-200-198.3-195.5-195.5-190-185-184
d0.87920.85370.83090.82970.81030.80420.78740.76220.7576


The latent heats of evaporation (in calories per gram) are given in the following table:

Latent heat of evaporation of liquid nitrogen

° C-148.08-148.61-149.75-153.65-161.20-173.73-182.51-195.09-200.03-205.45-208.36
T.° abs.125.01124.48123.34119.44111.8999.3690.5878.0073.0667.6464.73
l cals. per gram9.1711.4015.0322.9631.7339.6343.0947.0648.6450.5251.64


These latent heats may be represented by the formula

l2 = 89.962(TC - T) - 1.47242(TC - T)2 + 0.011666(TC - T)3.

The specific heat of liquid nitrogen at -200.4° C., and also at -209° C., is 0.476.

Surface Tension

This was first determined at -196° C. as 8.514 dynes per cm., while the variation with temperature is as follows:

t° C.-203-193-183
γ dynes/cm.10.538.276.16


The change in the molar surface tension with the temperature is given by

r(VM)2/3 = 2.002(124.29 - T),

in which VM is the molar volume M/D.

The temperature coefficient 2.002 is slightly below the mean value for normal liquids. The relation is rectilinear, as usual, up to a temperature a few degrees below the critical temperature (126° to 128° abs.).
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