RECENT ADVANCES IN SCIENCE 387 



scalenohedron (21 31). Nitric acid gave similar results. With 

 citric acid the order was (10I1), (1120), (21 31), and, after pro- 

 longed immersion, (10 10). Citric acid was the only common 

 acid to form pits on the scalenohedron, though the stronger 

 acids attacked it, giving the surface a glazed appearance. 



Crystallisation. — Several methods of determining the velocity 

 of crystallisation have been used in recent work. J. Czochralski 

 (Zeit. phys. Chem. 92, 219, 191 7) measures the velocity of 

 crystallisation by the maximum rate at which a crystal thread 

 can be drawn from a bath of the molten substance. Data for 

 the metals lead, tin, and zinc are given. R. Nacken (Centr. Min. 

 191 7, 191) has observed the growth of crystals of salol, from 

 an undercooled melt, under the microscope, and has measured 

 the rate of growth for different faces. A. Brann (Jour. Amer. 

 Chem. Soc. 40, 1168, 191 8) has continued his studies on the 

 effect of dissolved substances on the velocity of crystallisation 

 of water. The effects observed are explained as being due to 

 the influence of hydrates in solution. A further paper (ibid. 

 40, 1 1 84, 191 8) treats of the effect of dissolved substances on 

 the velocity of crystallisation of formamide. 



H. N. Holmes (Jour. Phys. Chem. 21, 709, 191 7) has in- 

 vestigated the formation of crystals in gels, and has obtained 

 crystals of metals such as copper and gold, as well as many salts, 

 from solutions containing silicic acid. In order to verify the 

 theory that some of the effects observed are due to capillary 

 action through the " pores " of the gels certain substances in 

 solution were allowed to diffuse through closely packed masses 

 of finely divided material such as alundum, well-formed crystals 

 being obtained. 



Historical. — In the Hugo Muller lecture to the Chemical 

 Society (Jour. Chem. Soc. 113, 363, 191 8), Sir H. Miers sum- 

 marised recent work in crystallography and mineralogy,, em- 

 phasising the contrast between the older work, which consisted 

 mainly in direct crystal measurement and mineral description, 

 and the present-day work, such as the X-ray analysis of crystals 

 and the researches of the Geophysical Laboratory. The June 

 number of The American Mineralogist (vol. hi. No. 6, 191 8) is 

 devoted to a description of the work of Haiiy, and the results 

 which proceeded directly and indirectly from it. Attention 

 may also be drawn to two articles in the centenary number of 

 the American Journal of Science, where W. E. Ford (Amer, 



