Nitrogen vapour pressure

A number of potential sources of error must be taken into account. In the volumetric method the following items need attention (a) constancy of the level of liquid nitrogen (b) depth of immersion of the sample bulb ( S cm) (c) temperature of sample (monitoring with vapour pressure thermometer close to sample bulb) (d) purity of adsorptive (preferably 99-9 per cent) (e) temperature of gas volumes (doser, dead space), controlled to 01 C. 

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

Figure 9.10 Nitrogen dioxide vapour pressure vs temperature...

Measurements in this held have been made by Berthelot and Ogier with nitrogen tetroxide Ann. de Chim. et Phys., [v.], 30, 382 (1883)), and with acetic acid ibid., 400), and some calculations with reference to steam have been made by Nernst Verhandl. Deutsch. Phys. Ges., 15, 313) and Levy ibid., 330), who utilised the vapour-pressure measurements of Holborn and Henning Ann. der Physik, (1906), 21 (1907), 22, 23). Wiedemann had previously observed that the specific heats of ethylbromide, ethyl-acetate, and benzene increase with temperature at about the same rate as that of nitrogen tetroxide at 200°. In the case of steam it was assumed that (i.) the polymerisation is to double molecules... 

This deceleratory reaction obeyed the parabolic law [eqn. (10)] attributed to diffusion control in one dimension, normal to the main crystal face. E and A values (92—145 kJ mole-1 and 109—10,s s-1, respectively) for reaction at 490—520 K varied significantly with prevailing water vapour pressure and a plot of rate coefficient against PH2o (most unusually) showed a double minimum. These workers [1269] also studied the decomposition of Pb2Cl2C03 at 565—615 K, which also obeyed the parabolic law at 565 K in nitrogen but at higher temperatures obeyed the Jander equation [eqn. (14)]. Values of E and A systematically increased... 

Helium vapour pressure and latent heat of evaporation The latent heat of evaporation L and the vapour pressure />vap are fundamental parameters when using these two cryoliquids in the refrigeration process. Figure 2.5 shows L of 3He and 4He as a function of temperature. Note that L ( 20.9 J/g for 4He) is very small in comparison, for example, with that of hydrogen (445 J/g) or of nitrogen (200 J/g). Note also the minimum at 2.2 K in the graph for 4He, in correspondence with the superfluid transition. 

Solid state investigations have been generally corroborated by solution studies. The X-ray structure of lithium N-methyl pscudoephedrates102 indicates the tetrameric aggregation in which the lithium atoms are chelated between oxygen and nitrogen (Figure 6). The structure in solution has been demonstrated to be tetrameric in benzene by means of vapour pressure osmometry (VPO, 37 °C) and cryoscopy (5.5 °C). 

Urea nitrate (UN), more properly called uronium nitrate, is an energetic salt, and as such would not be expected to have much vapour pressure however, it might be detectable due to evolved urea or nitrogen oxides. Detection of urea nitrate is essential because for over a decade it has been a frequent choice of terrorists. It was used in the bombing of the World Trade Center in New York City (Februaryl 993) and in many car bombings in Palestine. In 1992, the use of urea nitrate became so prevalent in bombings by the Shining Path that sales of urea were outlawed in Peru. 

TATP has such a high vapour pressure that it can probably be directly detected, whereas RDX has such a low vapour pressure that dogs alert on the bouquet of solvents used in its manufacture. Nitrate esters readily decompose to eliminate nitrogen dioxide (NO2). This can be a clue for canines and certainly is for chemiluminescence. 

For some purposes solid carbon dioxide ( dry-ice ), sublimation temperature —78.5 °C or mixtures of dry-ice and acetone (temperature —78 to —95 °C) are used as coolants. These are obviously not as efficient as liquid nitrogen and they should not be used with chemicals which have an appreciable vapour pressure at the appropriate temperatures. 

In an open test, the pressure measured will be,the pressure in the containment vessel. If the test is done with the containment vessel closed and the nitrogen pressure control system off, then any permanent gas produced by the reaction will cause the containment vessel pressure to rise. Thus a constant containment vessel pressure indicates a vapour pressure system and a rising containment vessel pressure indicates a gassy or hybrid system. 

The disadvantages of this mixture are its high vapour pressure resulting from the low boiling point of nitrogen dioxide, and its erosiveness. 

They remain liquid under normal, ambient operating conditions (moderate temperature, atmospheric pressure). Safety in storage and handling should also be considered. A storable liquid propellant should not have an excessively high vapour pressure at ambient temperature. The leading storable propellant uses dinitrogen tetroxide as oxidizer and a 50/50 mixture of hydrazine-unsymmetrical dimethylhydrazine (UDMH) as fuel [71], Nitrogen tetroxide and UDMH is another storable propellant mixture in use [73],... 

It is fairly generally believed that nitrosulphonic acid plays an important part in the lead chamber process for the manufacture of sulphuric acid (see p. 153). The vapour pressures of mixtures of sulphuric acid with nitrous or nitric acid or with both these acids, within the range occurring in the chambers, increase with the nitrogen acid content and with rise in temperature, and the total pressure is always higher than the sum of the individual pressures, especially when the sulphuric acid is concentrated, for nitric acid - sulphuric acid mixtures this may be explained 1 by the occurrence of the following... 

From a study of the vapour pressures of the mixed acids, Miles has concluded that the highest nitrogen content is to be achieved by nitrating with a mixed acid consisting of ... 

The most detailed research on nitration in the gaseous phase has been carried out by Wilson and Miles [69]. They concluded that there were no prospects of introducing this method in practice, since the nitrocellulose produced is non-homogeneous, and the nitration is inadmissibly slow. Thus, to reach a nitrogen content of 10% N by vapour phase nitration, at a vapour pressure of 16 mm Hg, a period of 48 hr was needed. 

Other compounds, containing sulphur or nitrogen, may be present in some oils (like onion, garlic).Investigations on the solubility of pure essential-oil components in carbon dioxide showed that the separation of terpene hydrocarbons and oxygenated derivatives by fractionated extraction is difficult, since their solubility behaviours and vapour pressures are almost the same. Saturating the CO2 with water as modifier can increase the differences in solubility [78],... 

Vapour Pressures and Critical Points ofEiquids XI Heterocyclic Nitrogen Compounds, Engineering Sciences Data Unit 77019, London, 1977. 

The results are plotted in Fig. 70. When compared with the isotherms of nitrogen, oxygen, carbon dioxide, or ethylene, there is no indication of abnormal polymerization. The subject was studied by C. Schlatter. The vapour pressure of solid nitric oxide at —160-6° is 168 mm. According to K. Adwentowsky, the vap. press., p, at different temp, are as follow ... 

This compound, prepared at liquid nitrogen temperatures, was found to undergo mildly explosive decomposition when its vapour pressure passed 50 millibar. The boiling point was not determinable. 

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