Andersen: properties of pyrophosphates 



325 



In the mixtures containing 50 and 75 per cent Mg2P207, some 

 of the crystals showed an undulatory extinction indicating zonal 

 structure. This is what should be expected of crystals formed 

 from melts where perfect equilibrium did not obtain through all 

 the period of crystallization. The lack of equilibrium was evi- 

 dent from the fact that the crystallization of these melts took 

 place with a considerable undercooling. At any rate, the in- 

 homogeneity of the mix-crystals due to zoning is not nearly 

 great enough to arouse suspicion of the separation of two dis- 

 tinct phases. The mixture containing 25 per cent Mg2P207 shows 

 perfectly homogeneous crystals and the undercooling of the melt 

 is insignificant. 



TABLE 3 



The optical character of all the mix-crystals is positive. The 

 axial angle varies according to composition. It is large in the 

 mix-crysta s containing 75 per cent Mn2P207; medium in the 50 

 per cent crystals and small in the 25 per cent crystals. 



The facts stated prove conclusively that the two phosphates 

 are perfectly miscible in the solid state and that the system 

 Mg2P207:Mn2P207 belongs to Roozeboom's Type I, the type 

 without a maximum or minimum. 



BOTANY. — The name of the wood-apple, Feronia Limonia. Wal- 

 ter T. Swingle, Bureau of Plant Industry. 



The wood-apple of India, Ceylon, and Farther India is a decidu- 

 ous tree with odd-pinnate leaves and globose fruits about the 

 size of an orange, with a hard, woody rind. It belongs to the 

 orange subfamily, Citratae, of the Rutaceae and is one of the 



