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. | | 120.9 | 64.51 | 2.507 | 86.21 | | 361.6 | 71.54 | 7.370 | 99.51 | | 561.3 | 74.83 | 21.82 | 117.62 | | 760 | 77.31 | 33.46 crit. pt. | 125.96 | | 938.6 | 79.18 | | | | 1591.1 | 84.21 | | |
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. | | -148.08 | 0.4314 | 0.18620 | | -149.75 | 0.4799 | 0.16380 | | -153.65 | 0.5332 | 0.11170 | | -161.20 | 0.6071 | 0.06987 | | -173.73 | 0.6922 | 0.02962 | | -182.51 | 0.7433 | 0.01558 | | -195.09 | 0.8043 | 0.00490 | | -200.03 | 0.8265 | 0.00278 | | -205.45 | 0.8499 | 0.00136 | | -208.36 | 0.8622 | 0.00089 |
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 | | d | 0.8792 | 0.8537 | 0.8309 | 0.8297 | 0.8103 | 0.8042 | 0.7874 | 0.7622 | 0.7576 |
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. | 125.01 | 124.48 | 123.34 | 119.44 | 111.89 | 99.36 | 90.58 | 78.00 | 73.06 | 67.64 | 64.73 | | l cals. per gram | 9.17 | 11.40 | 15.03 | 22.96 | 31.73 | 39.63 | 43.09 | 47.06 | 48.64 | 50.52 | 51.64 |
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. |
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. | 10.53 | 8.27 | 6.16 |
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.). |