Boiling point method

Molecular Weight Determinatioos. Details of the determination of molecular weights on a semi-micro scale by the Freezing-point method are given on p. 436, and by the Boiling-point method on p. 440. 

Although the boiling-point method is able to dispose of a greater numbei of convenient solvents than are suitable for freezing-point determinations, it is never so accurate, mainly on account of the difficulty of avoiding fluctuations in the boiling-point, due to radiation, to the dripping of cold liquid from the condenser, to impure solvent, and to barometric fluctuations. 

Boiling-point method, 37 determination of, 58 correction for, 59 / 1 iroinacetanilicle, 152 Bromacetic acid, 8g Broiiiaceiyl bromide, 89 Bromuhenzene, 140 y /-Bromobenz.oic acid, 201 Brouiocresol, 165 / Bromoioluene, 167 Butyric acid, 99... 

The first five measure the activity of the solvent and the last five measure the activity of the solute. The boiling point method is generally not included in evaluations for two reasons there are little data from these measurements or the thermal data are not adequate to apply an accurate correction to obtain an activity at 298 K. 

Tabus II, 9, B.—Reference Substances for the Calibration of Thermometers by the Boiling Point Method... 

Calcium sulphate, as desiccant, 41, 141 Calibration curve of thermometer, 229 Calibration of thermometers, 72-75 reference substances for, by boiling point method, 74... 

In spite of the wealth of information available on the preparative and structural aspects of the lanthanide chlorides (1-3), experimental thermodynamic, and, in particular, high-temperature vaporization data are singularly lacking. The comprehensive estimates of the enthalpies of fusion, vaporization, heat capacities and other thermal functions for the lanthanide chlorides by Brewer et ah (4, 5) appear internally consistent, but the relatively few experimental measurements (6-/2) do not permit confirmation of the estimates due to the narrow temperature ranges of study. Additionally, the absence of accurate molecular data for the gaseous species has hampered third-law treatment of the limited experimental vapor pressure data available. The one reported study (12) of the vaporization of EuC12 effected by a boiling-point method lacks accuracy for these reasons. 

Structural Formulas Boiling Point Method Yield (%)... 

The vapour pressures of all lanthanide trifluorides have been measured, including P111F3. Various techniques have been used, which can be divided in indirect techniques (effusion and boiling point methods) which provide accurate data for the total vapour pressure, and direct mass spectrometric techniques, which are less precise, particularly in case of quadrupole mass spectrometry, but give information on the vapour composition and the presence of dimeric or polymeric molecules or dissociation products. 

The molecular weight of cobalt chloride as determined by the freezing-point method, with urethane as solvent, corresponds to the double formula, Co2Cl4 (compare ferrous chloride),1 but the results obtained by the boiling-point method 2 indicate that under those conditions the molecule is single, namely, CoCl2. 

Ballast bulb (5 L) pressure gauge three long pieces of heavy-wall rubber pressure tubing. If the boiling-point method is used distillation flask appropriate thermometer to cover the desired range, with one-hole rubber stopper to allow adjustment of thermometer... 

The vapour pressures of metals at high temperatures have been determined by the boiling-point method under various pressures of indifierent gas, by the efflision method ( 12.VIII J), and by other methods. ... 

Van Wijk and Seeder s viscosity equation, 91 vapour, density of saturated, 324 specific heat of saturated, 336, 346-7, 359 vapour pressure 226 alignment chart, 271 of aliphatic esters, 286 of alkali halides, 237,243 of benzene, 267 boiling-point method for, 235 in capillary tubes, 367 of carbon, 246 centri fugal force, effect of, on 292 constant, 335, 341 over curved surface, 366 determination of, 227-47 dew-point method, 241 of dibasic acids, 243 dynamical method, 235 effusion method, 241. electrification, effect of on, 238, 375 of elements 257 of esters, 250 f., 286 of fusible metal, 230 in... 

Due to lack of data on vapor compositions over PbF2 at various temperatures, the total pressure measurements reported by Wartenberg and Bosse (2.), using boiling point method, and those of Nesmeyanov and lofa (2) are not used for evaluation. 

The boiling point method is also often called the effusion method in the literature. There are two variations of the boiling point method. In the first, the temperature is increased slowly at constant pressure, and in the second, the external pressure is decreased slowly at constant temperature. In the isothermal method, difficulties associated with superheating... 

Boiling usually implies vapor bubble formation in a liquid. Since the method is also applicable to solid samples, it may seem inappropriate to call it the boiling point method. However, in this context, the term boiling may be taken to mean the evolution of vapor from a condensed sample when its saturated vapor pressure is equal to the external pressure. The term boiling point then refers to the temperature at which the vapor pressure equals an arbitrarily chosen external pressure, and not only 101.325 kPa. 

The boiling point method connected with the evaluation of experimental results according to the method of Motzfeldt et al. (1977) was applied to the determination of vapor pressure of various molten salt systems at a temperature range of 600-1200°C. The most accurate results were, however, obtained by computer fitting of the complete Eq. (7.19) using a sophisticated computer program developed by Hertzberg (1983). 

The boiling point method using the apparatus described was applied to a number of cryolite-based melts, in the following studies... 

The boiling point method originated from Ruff and Bergdahl (1919) and was further developed by Ruff (1929). The principle of the isothermal method is as follows. The system to be investigated is taken in a cell (crucible) with a narrow capillary opening in the lid. The cell is suspended from a balance into a furnace with an inert gas atmosphere at constant temperature. The initial pressure of the inert gas is higher than the equilibrium... 

The transpiration method is a simple and versatile method for vapor pressure measurement at high temperatures. An inert carrier gas is passed over the condensed substance in a constant temperature furnace zone. The flow rate of the carrier gas is constant and sufficiently small so that the carrier gas is saturated with vapor, which condenses at some point downstream. The mass of vapor transported by a known volume of carrier gas is determined. If the total vapor pressure is known, from the boiling point method, the results from the transpiration method may be used to calculate the average molar mass of the vapor. 

Similarly as in the theoretical treatment of the boiling point method discussed in Section 7.2.1.1., the correct transport equations for a binary gaseous mixture with gradients in both composition and total pressure are also applied to the case of the transpiration... 

For the explanation of parameters A, C, and y, look into the theory of the boiling point method. The above equations consider diffusion and flow of vapor only through the exit capillary of the apparatus. The equations become very complex when the diffusion upstream through the entrance capillary is taken into account. Their application is not practical, as they contain too many unknown parameters. 

In connection with soap solutions it is impossible to use the ordinary boiling point method owing to the presence of a large amount of air which does not escape from the bubbles and therefore by its partial pressure, invalidates the results This is a cnticism of Krafft s well-known boiling point observations on soap solutions,andequally invalidates... 

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