636 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that as liquid amber is so difficult to obtain, recourse must be had to- 

 styrax. The double iodide of mercury and potassium, which is miscible- 

 with water, is useful for rapid examination of valves or frustules, the 

 structure of which is to be examined as soon as they are taken from 

 water. It is a dangerous liquid, and care must be taken that it does not 

 come in contact with objectives as the mounting of the lenses may be 

 attacked. Smith's arsenical medium should be reserved for the examina- 

 tion of ultra-difficult details. 



(6) Miscellaneous. 



Mabk, E. L. — Electric Wax-cutter for Use in Reconstructions. [Describes an 

 ingenious machine for cutting out the wax plates, intended for the reconstruc- 

 tion of objects, by means of an electrically heated wire.] 



Proc. Avier. Acad. Arts and Sci., xlii., 1907, pp. 629-36 (3 figs.) 



Metallography, etc. 



Evolution of Modern Tool Steel.* — H. C. H. Carpenter deals with 

 some questions raised in F. W. Taylor's recent paper.j He considers 

 that hardened steel is some form of combination of carbon with a solution 

 of carbon in either /3- or a-iron or both, and has an acicular micro- 

 structure. The best treatment of high-speed steels consists in heating 

 to a very high temperature, cooling rapidly to about 815° C, then at 

 a moderate speed to cold, and re-heating to about 620° C. The tool 

 after this treatment is a mixture in which there is present some y-iron, 

 the remainder consisting of an almost structureless material, probably of 

 an extremely fine and hard martensitic type. Chromium is an in- 

 dispensable constituent of high-speed steel, and appears to bring about a 

 condition of complete solution of the constituents. Carbon content may 

 vary within wide limits. It is suggested that a cutting test with a tool 

 maintained at a temperature over 900° C. would give valuable results. 



Magnetic Behaviour of Certain Nickel Alloys.^ — B. V. Hill has 

 determined the temperature of magnetic transformation of alloys of 

 nickel, to test the applicability of van 't Hoff's law relating to the 

 lowering of the freezing-point of a liquid by dissolved substances, to the- 

 lowering of the transformation-point of a magnetic metal by the addition 

 of another metal. The transformation takes place over a wide tempera- 

 ture interval. The following results were obtained for the transforma- 

 tion temperatures of the nickel-copper alloys : — 



* Engineering, Ixxxiii. (1907) pp. 569-71 and 633-4 (9 figs.). 



t See this Journal, 1907, p. 251. 



X Physical Review, xxiv. (1907) pp. 821-36. 



