118 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The film placed on the slide is examined under the Microscope by 

 transmitted light ; quite high powers may be used, and photomicrographs 

 taken. The illumination should be oblique, the mirror being shifted 

 until the best effect is obtained. Though such collodion films have long 

 been used in the measurement of microscopic objects, and by botanists f< >r 

 copying the cuticular surface of living plants, Nathorst was the first to 

 employ the method in the study of fossils. 



Rawitz' Microscopical Technique.* — This manual, by B. Eawitz, 

 aims at giving as complete an account as possible of the present con- 

 dition of microscopical technique, in a handy form, and suitable for 

 reference in the laboratory. The work is divided into two parts, the first 

 dealing with the various methods of research, and the second with the 

 application of these methods to the different organs and tissues. The 

 volume is but little adorned with illustrations, there being but eighteen 

 altogether, and all of them old friends. 



Metallography, etc. 



Melting Point Diagrams of the Binary Systems Galena- 

 Magnetic Pyrites and Galena-Silver sulphide.f— K. Friedrich has 

 employed for this work lead sulphide with «7 " 1 p.c. Pb, magnetic 

 pyrites with 62*35 p.c. Fe, and silver sulphide with 99*6 p.c. Ag 2 S. 

 Both equilibrium diagrams are simple, consisting of two branches 

 meeting at the eutectic point, and the horizontal eutectic line. A lower 

 horizontal at 175° C. in the galena-silver sulphide diagram indicates a 

 transformation point in AgjS. The melting points are, lead sulphide 

 1114° C, magnetic pyrites "l 187° C, eutectic (70 p.c. PbS) *63° C, 

 silver sulphide 835° C, eutectic (77 p.c. Ag.,S, 23 p.c. PbS) 630° C. 

 Photomicrographs are given. 



Melting Point Diagrams of the Binary Systems, Silver sulphide- 

 Copper sulphide and Lead sulphide-Copper sulphide.^ — K. Friedrich 

 gives the equilibrium diagrams. Ag. 2 S and Cu 2 S appear to form an 

 unbroken series of mixed crystals. A minimum occurs at 70 p.c. AgoS 

 (677° C), there is no eutectic. 1121° C. is the melting point of copper 

 sulphide. The lead sulphide-copper sulphide diagram has two branches 

 meeting at the eutectic point 51 p.c. Cu 2 S, 540° C. No ternary com- 

 pounds exist. A dilute solution of iodine in potassium iodide was 

 used for etching the sections. 



Influence of Stress on the Corrosion of Iron.§ — Walker and 

 C. Hill measured the potential given by pure Swedish iron, stressed in 

 tension in a testing machine, against a normal calomel electrode, in 

 ferrous sulphate solution. Below the elastic limit the potential change 

 is exceedingly small. Somewhere above the elastic limit the potential 

 rises suddenly. Out of a considerable number of specimens broken in 



* Leipzig : W. Engelniann (1907) 438 pp. 

 + Metallurgie, iv. (1907) pp. 479-85 (21 figs.). 

 X Tom. cit., pp. 671-3 (7 figs.). 

 § Mechanical Engineer, xx. (1907) p. 155. 



