Chemistry and Physics. 67 



in water, effloresce at 60° to 70°, fuse at 92° to an opaque mass, 

 sometimes exploding. Cryoscopic examination established the 

 molecular mass corresponding to the above formula. The interest 

 attaching to this compound is due to the fact that it is isomeric 

 (metameric) with hydrogen ammonium phosphite, a salt formed by 

 Amat in 1887 by neutralizing phosphorous acid with ammonia 

 and which has the formula NH 3 . H 3 P0 3 . On evaporating its 

 solution on the water bath, this salt separates in crystals belong- 

 ing to the monoclinic system. These crystals may be heated to 

 100° without change and fuse with partial decomposition at 123°. 

 Harden has noted the fact that this is not the first instance of this 

 sort, since Rohrig's sodium-potassium sulphites and Schwicker's 

 thiosulphates are also structurally isomeric. — Per. Berl. Chem. 

 Ges., xxx, 285, February, 1897. g. f. b. 



5. The Phase Pule ; by Wilder D. Bancroft. 8vo, pp. viii, 

 255. Ithaca, K Y., 1897. (The Journal of Physical Chemistry.) 

 $3. — Classifying the work done in Physical Chemistry under the 

 heads of Qualitative Equilibrium, Quantitative Equilibrium, 

 Thermochemistry and Mathematical Theory, the author has 

 sought in the present volume to present the subject of qualitative 

 equilibrium from the point of view of the Phase Rule and of the 

 Theorem of Le Chatelier, without the use of mathematics. He 

 defines a phase as a mass chemically and physically homogeneous, 

 i. e., a mass of uniform concentration ; and the components of a 

 phase as the substances of independently variable concentration 

 contained in the phase. Now according to the Phase Rule of 

 Willard Gibbs, the state of a phase is completely determined if 

 the pressure and temperature, together with the chemical poten- 

 tials of its components, be known. Hence the phase may be 

 described by an equation connecting these quantities; while for 

 every other phase in equilibrium with this, there will be another 

 equation containing the same variables. The number of such 

 equations therefore will be the same as the number of phases; 

 while the number of independent variables will equal the num- 

 ber of components plus the temperature and pressure. If n rep- 

 resent the number of components, the number of variables will 

 be n + 2\ and in a system of n + 2 phases there will be as many 

 theoretical equations as there are variables. In other words, each 

 of the variables has one value and one only for a given set of 

 n + 2 phases. A given combination of n + 2 phases can exist at 

 one temperature and one pressure only, the composition of the 

 phases being also definitely determined. Such a system is called 

 a non-variant system, the temperature and pressure at which 

 alone it can exist being known as the inversion temperature and 

 pressure. If the number of phases be n + \ however, the system 

 is no longer completely defined, has one degree of freedom and is 

 called a monovariant system. In this system for a given combi- 

 nation of phases there is for each temperature one pressure and 

 one set of concentrations for which the system is in equilibrium; 

 for each pressure, one temperature and one set of concentrations ; 



