218 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of different diluents, and to discover a means of ensuring evenness of 

 distribution of the organisms over the surface of the cytometer held. 



A. Cunningham* discusses the use of agar and gelatin plates for the 

 enumeration of organisms in milk, soil, etc. He points out that on 

 plates at 22° C. fresh colonies continue to appear on plates until the 

 tenth day, so that counting of colonies at an earlier date gives wrong 

 results. Liquefying organisms will, under ordinary circumstances, spoil 

 a gelatin plate in four or five days, but if liquefying colonies, whilst still 

 young, are touched with a fine silver nitrate point, as suggested by 

 Hiltner and Stormer, further liquefying is prevented and the plate after 

 ten or eleven days is still fit for counting. In platings from dung and 

 soil, more organisms, as a rule, are found on gelatin plates than on agar 

 at 22° C. In the case of milk more colonies appear on the agar than on 

 the gelatin plates. 



Metallography, etc. 



Annealing of G-old.j — T. K. Rose shows that when hard-rolled 

 plates of pure gold, consisting microscopically of thin parallel laminae, 

 are annealed, re-crystallization does not take place simultaneously 

 throughout the mass, but occurs first in particular laminae. Photo- 

 micrographs of partially annealed gold plates are given, showing some 

 laminae largely converted into minute crystals, while others remain 

 unchanged. 



Metallography of Commercial Zinc.+ — (i. Rigg and G. M. Williams 

 describe the microscopic appearance of the common impurities of zinc. 

 Iron occurs as well-formed crystals, which are probably a solid solution 

 of zinc and FeZn 7 . Lead appears as small black globules, or as a black 

 network if present in sufficient quantity. Cadmium is present in solid 

 solution up to 1 p.c, and forms a eutectic at higher concentrations. 



Copper-rich Kalchoids.§ — S. L. Hoyt has investigated the equi- 

 librium of the copper-tin-zinc system in the range 0-50 p.c. zinc 

 0-30 p.c. tin, and describes the microstructure of the alloys. The 

 addition of tin to the brasses causes the visible breakdown of the (3 

 solid solution. The microstructure of the ternary alloys corresponds 

 closely to that of the two binary systems. Two etching reagents were 

 used, basic cuprous chloride, suitable for the zinc-rich alloys, and acid 

 ferric chloride, preferable for the tin-rich alloys. Both reagents attack 

 the copper-rich constituent first and leave the y a bright grey. 



Molybdenum-cobalt Alloys. || — U. Raydt and G. Tammann describe 



the microstructure of the alloys used in their thermal study of this 

 svstem. With 25 p.c. or less molybdenum, cored polyhedric structures 



* Journ. of Hygiene, xiii. (1914) pp. 433-7. 



f Journ. Inst. Metals, x. (1913, 2) pp. 150-74 (9 figs.). 



J Proc. Amer. Soc. for Testing Materials, xiii. (1913) pp. 669-98 (25 figs.). 



S Journ. Inst. Metals, x. (1913, 2) pp. 235-74 (48 figs.). 



\\ Zeitschr. Anorg. Chem, lxxxiii. (1913) pp. 246-52 (1 fig.). 



