Non-formation of double salts, 272. Formation of double salt, 273. Transition interval, 277. Isothermal evaporation, 278. Crystallization of double salt from solutions containing excess of one component, 280. Formation of mixed crystals, 281. Application to the characterization of racemates, 282. _Representation in space._ Space model for carnallite, 284. Summary and numerical data, 287. Ferric chloride--hydrogen chloride--water, 290. Ternary systems, 291. The isothermal curves, 294. Basic Salts, 296. Bi_{2}O_{3}--N_{2}O_{5}--H_{2}O, 298. Basic mercury salts, 301. Indirect determination of the composition of the solid phase, 302. CHAPTER XVII ABSENCE OF LIQUID PHASE 305 Iron, carbon monoxide, carbon dioxide, 305. CHAPTER XVIII SYSTEMS OF FOUR COMPONENTS 312 Reciprocal salt-pairs. Choice of components, 313. Transition point, 314. Formation of double salts, 315. Transition interval, 315. Graphic representation, 316. Example, 317. Ammonia-soda process, 320. Preparation of barium nitrite, 327. Barium carbonate and potassium sulphate, 328. APPENDIX EXPERIMENTAL DETERMINATION OF THE TRANSITION POINT 331 I. The dilatometric method, 331. II. Measurement of the vapour pressure, 334. III. Solubility measurements, 335. IV. Thermometric method, 337. V. Optical method, 338. VI. Electrical methods, 338. NAME INDEX 341 SUBJECT INDEX 345 * * * * * {1} THE PHASE RULE CHAPTER I INTRODUCTION General.--Before proceeding to the more systematic treatment of the Phase Rule, it may, perhaps, be not amiss to give first a brief forecast of the nature of the subject we are about to study, in order that we may gain some idea of what the Phase Rule is, of the kind of problem which it enables us to solve, and of the scope of its application.