RECENT ADVANCES IN SCIENCE 547 



34). The decomposition has been carried out at the lowest 

 possible temperature and under diminished pressure, and the 

 primary products were at once removed, thus avoiding or 

 reducing to a minimum, any side reactions ; it was found 

 that tartaric acid at first loses one molecule of water, producing 

 a colourless lactide ; this is followed at a somewhat higher 

 temperature by an intra-molecular rearrangement whereby 

 hydrogen and hydroxyl change places, and the resulting com- 

 pound thereupon breaks down in one of two ways to produce, 

 in the one case acetic acid and carbon monoxide and carbon 

 dioxide, and in the other carbon dioxide and pyruvic acid. 



CBYSTALLOGRAFHY. By Alexander Scott, M.A., D.Sc. 



A. W. Hull has published a preliminary note on his 

 investigations of the structure of certain metals {Science, 52, 

 227, 1920 ; Jour. Cheni. Soc, 120, ii, 38, 1921). Calcium is 

 composed of face-centred cubic lattices, so that each atom has 

 twelve others equidistant from it. Some of the elements of 

 the eighth group, such as platinum, palladium, and iridium are 

 similar to calcium, but ruthenium has a structure like that of 

 zinc and cadmium. The latter two elements have structures 

 which conform to close-packed hexagonal aggregates, the 

 elongation of the unique axis being 14 per cent, and 16 per cent, 

 respectively. Titanium and tantalum belong to the centred 

 cubic type. Iridium is composed of a face-centred tetragonal 

 lattice, the elongation of the unique axis being 6 per cent. 



By the examination of X-radiograms of graphite, from grey 

 pig-iron, and temper carbon, from annealed white cast-iron, 

 K. Jokibe {Sci. Rep. Tohoku Univ., 9, 275, 1920) deduces that 

 the structure of each of these forms of carbon is the same as 

 that of natural graphite. Hence, temper carbon cannot be 

 regarded as amorphous. 



The structure of antimony has been investigated by R. W. 

 James and N. Tunstall {Phil. Mag. [vi], 40, 233, 1920), and the 

 crystals have been found to consist of two interpenetrating 

 face-centred lattices. The arrangement of the latter is such 

 that the atoms constituting one of the lattices lie on the 

 " trigonal " diagonals of the rhombohedral cells which form 

 the unit of the other lattice. In order to reconcile the structure 

 with the observed results, it is necessary to assume that the 

 atoms of the second lattice do not occupy the vacant corners 

 of the first, but are displaced a short distance along the diagonal. 



According to W. L. Bragg {ibid, [vi], 39, 647, 1920), zinc 

 oxide consists, so far as the crystalline form is concerned, of two 

 interpenetrating hexagonal lattices, with zinc as the constituent 

 particles, and two similar ones composed of the oxygen atoms. 



