MIXED FUSION ANALYSIS 



and McCrone. A contact preparation be- 

 tween the reagent (2,4,7-trinitrofluorenone) 

 and the unknown estabhshes if the unknown 

 is of the class which forms addition com- 

 pounds with the reagent. If an addition com- 

 pound forms, the preparation is observed 

 microscopically on heating. Identification is 

 achieved on the basis of melting point of the 

 unknown, the molecular addition compound, 

 the eutectic between the reagent and the 

 addition compound, and the eutectic be- 

 tween the addition compound and the un- 

 known. Besides these four melting points the 

 color of the addition compound is also ob- 

 served. In several systems the addition com- 

 pound was found to exist in two polymorphic 

 forms, hence additional melting points are 

 available for characterization. This method 

 is rapid and is applicable to liquids as well 

 as solids. It is also applicable if the addition 

 compound melts incongruently. 



The above identification scheme has been 

 applied to alcohols by Laskowski and 

 Adams. Although the alcohols do not gener- 

 ally form addition compounds, they may be 

 converted to 2,4,6-trinitrobenzoates. The 

 2,4,6-trinitrobenzene grouping leads to ad- 

 dition compound formation with a variety 

 of aromatic substances. Contact prepara- 

 tions w^ere made between various trinitro- 

 benzoate esters and both naphthalene and 

 phenanthrene as reagents. Four significant 

 temperatures (three if the addition com- 

 pound melts incongruently) were obtained 

 with each ester and each reagent. Satisfac- 

 tory discrimination was achieved among all 

 all of the alcohols investigated. The proce- 

 dure of reacting a functional group with a 

 suitable reagent so that the resultant deriva- 

 tive forms addition compounds with other 

 reagents offers promise for wide applicability 

 of this method of identification. 



Method of Mixtures. Mixtures of known 

 composition may be prepared by weighing 

 the components together and grinding until 

 a uniform composition is achieved. Since 

 only small amounts of material are required 



for determination of a melting point with a 

 hotstage microscope, it is possible to deter- 

 mine temperature-composition diagrams 

 rapidly with a minimum expenditure of ma- 

 terials. The points of initial and final melt- 

 ing are easily determined microscopically. 

 In addition it is frequently possible to ob- 

 serve polymorphic transitions in one or both 

 of the starting components. 



In such mixtures, it is also possible to 

 determine microscopically the effect of com- 

 position and temperature on crystal growth 

 velocity, nucleation rate, rate of nucleation 

 and growth of unstable polymorphic forms, 

 and the effect of added components on crys- 

 tal habit. The method of mixtures is appli- 

 cable to any number of components. 



SELECTED REFERENCES 



The literature on microscopic mixed fusion 

 analysis as well as the various experimental tech- 

 niques involved is covered extensively in the 

 books by Kofler (1) and McCrone (2) and the re- 

 view by Cecchini (3). Specific applications of 

 mixed fusion analysis include the identification of 

 aromatic compounds (4), the investigation of 

 molecular compound formation (5), (6), isomor- 

 phic relations between organic compounds of 

 sulfur and selenium (7), identification of alcohols 

 (8), identification of fibers (9), effect of composi- 

 tion on crystal habit (10), and studies on crystal 

 growth velocity (11). 



Although this list of references is not intended 

 to represent an exhaustive survey of the literature 

 on microscopic mixed fusion analysis, it does serve 

 to orient the reader in the general area. 



1. Kofler, L., and Kofler, A., "Thermo- 



Mikro-Methoden zur Kennzeichnung Or- 

 ganischer Stoffe und Stoffgemisch," Wag- 

 ner, Innsbruck, 1954. 



2. McCrone, W. C. Jr., "Fusion Methods in 



Chemical Microscopy," Interscience Pub- 

 lishers, New York, 1957. 



3. Cecchini, M. A., Selecta Chimico, 16, 95 



(1957). 



4. Laskowski, D. E., Grabar, D. G., and 



McCrone, W. C. Jr., Anal. Chem.. 25, 1400 

 (1953). 



5. FtJRST, H., AND Praeger, K., Chem. Tech., 



11, 653 (1958). 



6. Laskowski, D. E., and McCrone, W. C. Jr., 



Anal. Chem.. 26, 1497 (1954). 



45 



