36-^ X. E. A. Hinds — An Alkali Gneiss. 



3. "While the exact geological relations of the Van Nest 

 Gap rock are unknown, its chemical composition place it 

 with the dark colored variety of the Byram member of the 

 New Jersey pre-Cambrian gneisses. 



4. The Byram gneiss is considered to be an igneous rock 

 in which foliation developed in the magma during the 

 process of crystallization. 



5. Alkaline gneisses from other localities are cited, 

 and the scarcity of this type of foliates is emphasized. 



Mineralogical Laboratory, 

 Harvard University. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry and Physics. 



1. The Double Decomposition of Salts in Connection tvith the 

 Phase Rule. — Two or three years ago it was announced by 

 Etienne Rengade that in accordance with the phase rule a small 

 quantity of water acting upon an excess of two salts with four 

 different radicals or ions would necessarily cause the appearance 

 in the solid condition of a third salt, one of the two other possible 

 combinations of the ions. In contradiction to this statement 

 Ravenau has recently stated that a mixture of NaNOg and NH^Cl 

 could exist without decomposition in the presence of a small 

 quantity of water. Rengade has now shown, however, tliat this 

 statement is incorrect, for he has found, both by microscopic 

 examination and by analysis of the products of the treatment, 

 that crystals of NaCl are formed in this case. He has found 

 that NH.NOo and NaCl give NH.Cl as the third solid product, so 

 that there are at ordinary temperature two ternary mixtures 

 containing these four ions : 



XaNO, + NH.Cl + NaCl 

 and NH.NOg + NaCl + NH.Cl. 



He states that these can exist without change in contact with a 

 small quantity of water, and that every other mixture of two, 

 three or four of the salts containing the four ions will decompose, 

 giving, according to their proportions, one or the other of the 

 triple mixtures. 



Rengade admits, however, that it is possible for two salts with 

 different ions to remain in equilibrium without the formation of 

 a third salt in the solid state. This is the case when the two salts 

 are considerably less soluble than those formed by double decom- 

 position. Consequently it is to be observed that his original 



