ZOOLOGY AN 1 1) BOTANY, MICROSCOPY, ETC. 525 



Drawer Units of stout card, covered with book-cloth, are made on a 

 somewhat similar plan, except that each drawer is a separate " unit " for 

 72 slides. They consist of an outer sheath measuring 8 x 4 J x 3|- in., 

 with a drawer with cutaway sides, and handle with space for contents 



Fig. 77. 



card at front, and contain twelve trays, each to hold six 3x1 in. slides 

 in separate divisions. They are very durable, and a number may be 

 arranged in any desired manner, as the collection of slides grows. 

 Similar " units " are made without trays, and with drawers not cut down 

 at the sides ; they are useful for storing the various oddments incidental 

 to microscopical work (fig. 77). 



Metallography, etc. 



Cobalt-gold Alloys.* — AY. Wahl has determined the equilibrium 

 diagram of this system by thermal and microscopical methods. Obser- 

 vations were also made on magnetic properties and crystalline form. 

 Cobalt and the cobalt-rich alloys exhibited super-cooling to a remarkable 

 degree. The super-cooling of cobalt appeared to increase with greater 

 purity of the metal, and amounted to 200° C. in one experiment. In- 

 oculation was employed in taking cooling curves. No compounds exist 

 in the system, at either end of which mixed crystals, saturated at low 

 concentration, occur. The eutectic melts at 997° C. and contains 90 p.c. 

 gold. 



Lead-tin Alloys.| — W. Guertler suggests, in view of the results 

 obtained by Rosenhain and Tucker, and by Degens, that the evolution 

 of heat at about 150° C. may either be due to the decomposition of 

 mixed crystals of lead and tin or to the formation of a compound of 

 about the composition Sn 3 Pb 4 . The author has calculated the heats of 

 fusion of different lead-tin alloys from published data, and finds them 

 much greater than the means of the heats of fusion of the components. 

 Heat is therefore evolved when molten lead and tin are mixed. 



Nickel-carbon Alloys.; — K. Friedrich and A. Leroux have deter- 

 mined the melting-point diagram of the nickel-carbon system for the 

 range to 2*6 p.c. carbon. The alloys contained 0*2 to 0'6 p.c. iron. 



* Zeitschr. Anorg. Chem., lxvi. (1910) pp. 60-72 (3 figs.). 



f Zeitschr. Elektrochern., xv. (1909) pp. 953-65, through Journ. Chem. Soc, 

 xcviii. (1910) p. 126. 



% Vietallurgie, vii. (1910) pp. 10-13 (7 figs.). 



