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OF CONTENTS Introduction Techniques Kinetic studies Apparatus Applications-(2) Analytical chemistry (ii) Inorganic chemistry (iii) Organic chemistry Complementary procedures ConclusionTHERMAL methods of investigation, generally referred to as thermo-or thermal analysis or thenno-analytical techniques, have found wide application in recent years1 These may be defined as experimental methods for characterising a system (element, compound or mixture) by measuring changes in physico-chemical properties at elevated temperatures as a function of increasing temperature.2 The two chief methods are (a) differential thermal analysis,3 in which changes in "heat content" are measured as a function of increasing temperature and (b) thermogravimetric analysis, in which changes in weight are measured as a function of increasing temperature. Other methods that come within this definition involve the use of changes in gas volume or pressure; changes in solid volume; changes in electrical resistance ; changes in ultraviolet, visible or infrared transmission or reflectance.4The two techniques, (a) and (b), provide information relating to certain physical and chemical phenomena, which are listed below-

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The kinetics of the thermal decomposition of purified pyrite to pyrrhotitc and sulfur in a dynamic argon atmosphere have been studied over the temperature range 600 to 653 "C. T h e reaction was follo~ved by the rate of weight loss as indicated by a quartz spring balance and also by the rate of progression of the pyrite/pyrrhotite interface into a cylindrical, compressed, polycrystalline pellet. The temperature coefficient of the reaction was foiind to be 69.5 f 5.9, 64.7 f 3.3, and 66.9 f 5.1 kcal mole-I, when the results were processed in three different \\lays.The pyrite/pyrrhotite interface was found to progress a t a linear rate into the pellet a t a given temperature; eq~~atiorrs were derived to express the variation of reaction rate with temperature.--lttempts to follow the early nucleation stage ol the decomposition, using massive mineral crystals, proved unsuccessful.The thermal deconlpositioil of the mineral pyrite (FeS2) to yield pyrrhotite (FeS1+,) and sulfur has been made the subject of many investigations (1-13) ; this work has recently been reviewed by Kullerud and Yoder (1). Most studies have been made by measuring sulfur vapor pressure values ( p s ) under equilibrium conditions over a range of temperatures. The enthalpy, A H , of the reaction, obtained froin these measurements, has given values ranging fro111 39 to 104 lccal ~nole-I for various investigators, most values lying in the 05 to 85 ltcal mole-' range. 31Iost \vorl;ers employed static conditions a t less than 1 a t m pressure; I.tical treatment as that employed by i\IcI

A study has been made of the kinetics of the thermal decomposition of pyrite to pyrrhotite and sulphur in a dynamic argon atmosphere. The reaction was followed (a) by the rate of loss of weight as indicated by the extension of a quartz spring and (b) by the rate of progression of the pyriteipyrrhotite interface into a polycrystalline compressed pellet. The temperature coefficient of the reaction was found to be 69.5 ± 5.9, 64. 7 +- 3.3 and 66.9 ± 5.1 kcal. mole- 1 when the results were processed in three different ways. The pyriteipyrrhotite interface was found to progress at a linear rate into the pellet and equations were derived to express the variation of reaction rate with temperature. Attempts to study the early nucleation stage of the decomposition, using mineral crystals, proved abortive.