Freezing-point determination

Freezing-point Determination. — I n the example to be described, pure benzene (see p. 136) is used as the solvent. Carefully dry the inner tube. Fit it wuth a cork and weigh it together w ith the coik suspended by a wire to the aim of the balance. Intioduce sufficient benzene to cov er the bulb of the Beckmann thermometer when it is pushed nearly to the bottom of the tube. About 10 c.c. will be found to be sufficient. Insert... 

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. 

For density and freezing-point determinations on aqueous solutions of the acid, see de Coninok, Bull. Acad. roy. Bely., 1905, p. 150 Rosenheim and Krause, Zeitsch. anorg. Chem., 1921, ri8, 177 Manohot and Ortner, ibid., 1922, 120, 302. 

Attempts to determine the molecular weight of colloidal ferric hydroxide lead to very high values. Thus, a colloidal solution prepared by addition of ammonium carbonate to ferric chloride solution was purified by dialysis, and the freezing-point determined of that portion which would not pass through a collodion membrane. The point was only slightly lower than that of the filtrate, indicative of a molecular weight of 3120 for the colloid.2... 

Freezing-point determinations show that uranyl sulphate dissociates in (Mute solutions to a much less extent than the chloride or nitrate. 

Inasmuch as the project uses the physical properties for the identification of hydrocarbons and the determination of their purity, one of the functions of the project is to make accurat measurements of the physical properties of the highly purified API Research hydrocarbons. Beginning with the very important property of the freezing point, determinations are made of the density, refractive index, boiling point, and vapor pressure. 

Selenium boils at about 680°, forming a dark red vapor which may be condensed either as scarlet flowers of selenium or shining drops of molten substance. Vapor density measurements indicate the presence of associated molecules at lower temperatures, but at 900-950° the density indicates a molecular structure Se2 which is retained up to 1800°. Its molecules become monatomic at 2000°. Freezing point determinations indicate a molecule which is approximately Ses.1 On the basis of a diatomic vapor the latent heat of vaporization is 135.5 calories per gram, the heat of sublimation is 219.4 calories, and the heat of fusion 83.9 calories.2... 

Behaviour of the Ions—The osmotic pressure of the ions is less than that calculated from the gas law This is true m every case, except for solutions of litmum chlonde 01N and above, hydration is probably the cause of the exceptional behaviour The behaviour of ions may be represented within the error of the freezing point determinations by an equation of the form—... 

Foam fractionation Fractional extraction Fractionation, seeDistillation Free-volume theory of diffusion Freezing-point determination Fugacity of nitrogen standard state Fugacity coefficient composition dependence of acetic acid vapor... 

A similar analysis with L/ replaced by L , the molar heat of vaporization of the pure solvent, relates the boiling-point elevation for nonvolatile solutes to the activity coefficients and the solution molecular weight of the solute. Although more accurate results are obtained by use of freezing-point determination, the boiling-point method is often used when only a small quantity of the solution is available. 

Freezing-point determinations, on both dilute and concentrated solutions, show tliat, per mol of SO any increase in basic ratio over the normal salt raises the freezing-point. The osmotic effect of the sulphate is, therefore, always decreased by dissolving in it its own hydroxide. The electrical conductivity of the basic solutions is less than that of normal solutions containing the same amount of SO,. Migration experiments show that beryllium forms no part of the anion. The basic solutions are not precipitated by crystalloids but on dialysis hydroxide is left on the membrane, and the dialyzed solution has a lower basic ratio. 

The difference between a freezing point determined in the presence of air at a pressure of one atmosphere and the triple-point temperature will depend on the effect of dissolved air and on the pressure difference. The presence of dissolved gas in the liquid phase always lowers the transition temperature. The amount by which it does so can be calculated from the freezing point depression equations if the solubility is known and ideal behaviour is assumed. The effect of pressure can be calculated from the Clapeyron equation... 

To study the eutectic nature of the HER/HQEE blends, freezing point determinations were made. HER/HQEE blends were prepared at different weight ratios and melted at elevated temperatures. Then the melt was allowed to cool slowly under controlled conditions. The temperature at which the first crystallisation was observed was considered to be the freezing point of the melt corresponding to that particular HER/ HQEE composition. 

The critical micellar concentration of any detergent may be determined by a number of different methods, including the solubilization of insoluble dye, osmotic pressure, conductivity, surface tension, light scattering, nuclear magnetic resonance, refractive index, freezing point determination, vapor pressure, sound velocity, etc. (141). Each method may give a somewhat different value for CMC. 

The accirrate determination of freezing points by time-temperature analysis was extensively used by the American Petroleirm Institute Research Project 6 for the determination of the pirrities of hydrocarbon samples. Also, the method has been developed for determining the cryoscopic constant, from which the molar enthalpy of fusion can be calculated. Accirracy of freezing points determined by this method is estimated to be 0.01 K. However, inaccirracy of enthalpy of fusion estimated from the method is more than +10 percent, or even 50 percent in some cases. Especially, the method can not separate the enthalpy of a solid transition from the enthalpy of fusion if the temperatures of these phase transition are within a few Kelvin. 

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