Melting point diagram

It is instructive for the student to construct a rough melting point diagram (compare Section 1,13 and Fig. 1,12, 1) for mixtures of cinnamic acid and urea. Weigh out 1 00 g. each of the two finely powdered components, and divide each into ten approximately equal portions on a sheet of clean, smooth paper. Mix 4 portions of cinnamic acid (A) with 1 portion of urea B) intimately with the aid of a spatula on a glass slide, and determine the melting point (the temperature at which the mixture just becomes completely fluid is noted). Repeat the procedure for 3 parts of A and 2 parts oiB 2 parts of A and 3 parts of B and 1 part of A and 4 parts of B. Tabulate your results as follows —... 

Molten cryohte dissolves many salts and oxides, forming solutions of melting point lower than the components. Figure 1 combines the melting point diagrams for cryolite—A1F. and for cryohte—NaF. Cryohte systems ate of great importance in the HaH-Heroult electrolysis process for the manufacture of aluminum (see Aluminumand ALUMINUM alloys). Table 5 Hsts the additional examples of cryohte as a component in minimum melting compositions. 

Figure 1. Melting point diagrams for the three types of enantiomer systems (only the liquidus curves are shown).

The existence of a compound of ammonium thiocyanate and thiourea, NH4CNS.4CS(NH2)2, is indicated by the melting-point diagram.5 Ammonium thiocyanate forms a condensation product with formaldehyde, this being only sparingly soluble in water and ordinary solvents, and decomposed by strong acids or alkalis.6... 

The qualitative form of a congruent melting-point diagram is as follows (with hatch-marks in two-phase regions omitted for clarity) ... 

Figure 3 Melting-point diagram of the binary system phenol-p-toluidine (adapted from Ref. 29) as cited in Ref. 28.

Binary mixtures containing an m/ramolecular H bonded component often have normal melting point diagrams, compound formation being inhibited or absent. A striking example is shown in Fig. 5-4 (taken from 571). The o-nitrophenol-acetamide pair shows just a eutectic—the... 

FIGURE 5-4 Melting point diagrams for nitrophenol-acetamide mixtures. [From Dzhelomanova, Rudenko, and Dionis ev, J. Gen. Chm. U.S.S.R. 26,1866 (1956).]... 

Fig. 11. Melting-point diagram for the antimony trichloride-aluminum chloride system.

The melting point diagram (Fig. 10) indicates a rapid exchange process only for similar radicals 819). 

Fig. 10. Melting point diagram for NaAl(CH,)<-NaAl(C2H6)< system eutectic at 83°C (1 1 mixture) 319).

Alternatively, they can form a solid solution (a pseudoracemate) in which one enantiomer replaces the other at random in the packing arrangement. This situation, extremely rare in practice, would be characterized by either a maximum or a minimum in the melting point diagram and by the same X-ray powder diffraction pattern over the entire range of concentrations [15]. 

Solid-Liquid Phase Diagrams (Melting Point Diagrams)... 

Fig. 14.7 Melting point diagram of a system of two substances showing indifferent behavior in both the liquid and solid states (constructed using Fig. 14.6).

Fig. 14.8 Applying the lever rule in a melting point diagram for a system containing two substances that are indifferent in liquid and solid states.

Melting point diagrams with complete miscibility only appear when the form and size of the particles allow them to be inserted into a common lattice. Examples of this are copper/nickel as weU as the minerals fayalite (Fe2Si04)/forsterite (Mg2Si04). 

More Complicated Melting Point Diagrams More complicated phase diagrams can be developed by considering the ji x) curves of the participating components. 

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