Temperature of melting

A parallel thermodynamic study of 2-methylthia2ole was performed by Goursot and Westnim (299). The stable form was characterized by a temperature of melting of 248.42°K, an enthalpy of melting of 2907 cal mole and an entropy of melting of 11.70 cal mole ... 

Thermodynamic efficiency is hurt by the large ATbetween the temperatures of melting and freezing. In an analogy to distillation, the high a comes at the expense of a big spread in reboiler and condenser temperature. Erom a theoretical standpoint, this penalty is smallest when freezing a high concentration (ca 90%) material. 

The datum point, when considering the steam/water substance, is usually taken as water at the temperature of melting ice, at normal atmospheric pressure and so at a temperature of 0°C. Adding heat energy raises its temperature some 419.04kJ will raise 1 kg to 100°C, when any further addition of heat evaporates some of the water. If 2257 kJ are added to each kg of water, then all the water becomes the dry gas, steam. Equally, if only part of this extra energy is added - say, 90 per cent - then 90 per cent of the water evaporates and the other 10 per cent... 

The diazotized solution is poured into a 1.5-1. wide-mouth flask or bottle which is surrounded by ice water. Three hundred cc. of cold benzene is now poured into the diazonium solution, and by means of a good stirrer the two liquids are intimately mixed. The mixture, which is at the temperature of melting benzene, is now ready for the addition of alkali. 

The size of the degree alone remains to be fixed, and is quite arbitrary. To produce as little change as possible from the ordinary scale, Lord Kelvin divided the range of temperature between the absolute temperature of melting ice T0, and that of boiling water, Ti, into 100 equal parts, each of which is defined as one degree. 

At atmospheric pressure and at the temperature of melting ice, 32 gr. of oxygen occupy a volume of 22,412 c.c. (corrected for a slight deviation from the gas laws) ... 

Figure 3. Relation between weight-average molecular weight and absolute temperature of melting...

The trimethylated xanthine, caffeine, sublimes at 1800°C, which is a lower temperature of sublimation than theobromine.10 Temperatures of melting and sublimation are given in Table 1. 

Modern temperature scale proposed by G. Fahrenheit, defined by a thermometer, a law and three fixed points. Fahrenheit s thermometer was a mercury-in-glass one. Thermal expansion versus temperature was assumed linear. Three fixed points were defined 0°F temperature of a mixture of water, ice and ammonium chloride 32°F temperature of melting ice 96°F temperature of human body... 

The temperature of melting is usually not strongly affected by external pressure, but the pressure dependence can be expressed by the Clausius-Clapeyron equation ... 

To compounds which dissolve with difficulty in camphor, decompose at the temperature of melting, or react with camphor this method cannot, of course, be applied. In such cases use as solvent the hydrocarbon camphene,1 which melts at 49°. 

Fig. 3.46 (a) The temperature of melting and decomposition peaks of NaBH for all composites from Figs. 3.44 and 3.45 as a function of the MgH content. Numbers in parenthesis show the number of multiple data points for this specific composition. Data for the (NaBH + Xwt%Mg) mixtures where Xwt% is an equivalent amount of Mg corresponding to the Mg decomposed from Xwt%MgHj are also included, (b) Analysis of the yield of MgB based on the Vajo et al. [196-198] model adopted for the (NaBH + MgH ) system... 

DSC experiments were conducted up to 500 and 600°C for the ball-milled mixtures of NaBH with 12, 55, 73 and 92 wt%Mg (DSC traces not shown here). The temperatures of melting and decomposition peaks of NaBH are plotted in Fig. 3.46a. It is seen that the data points for the equivalent content of 12, 55 and 73 wt%Mg follow quite closely the data points for MgH. Only data points for the equivalent content of 92 wt%Mg show slightly higher decomposition temperature than their MgH counterpart and lie slightly above the ROM line for MgH. This behavior is probably related to different mechanical properties of Mg and MgH which results in different abilities to particle and grain size reduction during the milling process as can be seen in Fig. 3.47. The particle size reduction of ductile... 

P.-J. Macquer has left us, in his Dictionary of Chemistry, a fine first-hand account of the scientific history of this gem (255). On July 26, 1771, Macquer and Godefroy de Villetaneuse, in presence of Jean Darcet (1725-1801), Hilaire-Marin Rouelle (Rouelle the Younger), and others, heated a flawless diamond in a refractory capsule in Macquer s wind furnace. When it reached the temperature of melting copper, a flame could be seen surrounding it, and in less than an hour the gem disappeared without leaving a trace (257, 258, 259). 

This is suitable for the formulations in which the percentage of solid ingredients, suspended in liquid is to be increased. The advantage of density difference between the molten medium and suspended particles is used in this process. The concentration of heavier particles is increased in the lower part of the casing either by natural sedimentation or by forced sedimentation caused by vibrating the whole casting assembly. The sedimentation process is controlled by a number of parameters such as particle size of solid suspension, temperature of melt, period of sedimentation, viscosity of melt, concentration of solid ingredients and column of melt etc. 

One possible reason suggested by Flory and Mandelkern (1956) for or contribution to the discrepancies indicated in Table 2 is the inability of the penetrometer method to detect the maximum temperature of melting because of its relative insensitivity and because of the upper "tail to the crystallinity-temperature curve as deduced from the copolymer crystallinity theory of Flory (1955). Dole and Wunderlich (1957, 1959) found, however, that two melting regions each of the quenched 80/20 and 60/40 copolymers could be observed in the calorimetric experiments. The specific heat curves of these two copolyesters are illustrated in... 

Measure the temperature of melting ice, then repeat after adding salt to the ice. 

Double-helical DNA in solution can undergo strand separation or dena-turation as a consequence of extremes of pH, heat, or exposure to chemicals such as urea or amides. Decrease in viscosity, increase in absorbance at 260 nm (hyperchromic effect), decrease in buoyant density, or negative optical rotation indicates denaturation of DNA. The denaturation process disrupts only noncovalent interactions between the two strands of DNA. Since G-C base pairs are held together by three hydrogen bonds in contrast to two for an A-T base pair, A-T rich DNA is easily denatured compared to G-C rich DNA (Figure 6.3). Electron microscopy can detect these A-T-rich regions in a DNA molecule since they form bubblelike structures. Hence the temperature of melting (Tm) of DNA increases in a linear fashion with... 

---