ZOOLOGY AND BOTANY, MICROSCOPY, ' ETC. 257 



projects beyond the cutting edge of A when the scissors are open, but 

 when these are closed the spring is forced past the cutting edge. In 

 fig. 65 is shown a section through D, with an object X which is to be 

 cut. Inspection of this proves that when B and C meet, the object is first 

 held and then cut. 



Fig. 66 shows another weed-cutter, in the form of a guillotine, useful 

 for cutting and holding specimens in deep jars, etc. A is a square brass 

 tube, cut away at its lower end, as shown in the figure, with a slot in the 

 remaining side, leaving a cutting edge C ; beyond C is fitted a small 

 block D. A square plunger B fits this tube, having its lower end bevelled 

 to a square edge. This plunger is actuated by a rod sliding in the tube F, 

 and is kept raised by a spiral spring E (in a spring box H) against the 

 under side of the milled-head O. The instrument is plunged into the 

 jar of water containing the weed or other like object, which is caught in 

 the slot above mentioned. On pressing the milled head the plunger 

 descends, cuts the object as it passes the edge of the slot, and holds it 

 against the block D. On withdrawing the instrument and releasing the 

 spring the plunger rises, and the fragment which has been cut is released. 



Metallography, etc. 



Iron-tungsten System.* — H. Harkort gives a lengthy account of 

 the preparation of a large number of carbonless iron-tungsten alloys, 

 the determination of their solidification temperatures and critical ranges, 

 and their microstructure. A section of the paper deals with the theory 

 and construction of granular carbon resistance furnaces, one type of 

 which was used for the melting of the alloys. The Saladin double 

 galvanometer was used for the heating and cooling curves. Many of 

 the alloys obtained were inhomogeneous, and marked discrepancies 

 exist between the tungsten added and that found by analysis. The 

 freezing-point temperatures, though too irregular [to admit of the con- 

 struction of a reliable equilibrium diagram, point to the existence of a 

 compound. Ar2 and Ac 2 appear to be little affected by addition of 

 tungsten, while Ar 3 and Ac 3 are raised. 



Zinc and Nickel.f — V. Tafel has determined the equilibrium 

 diagram in the range 0-50 p.c. nickel. At about 60 p.c. nickel the 

 boiling-point and melting-point coincide. One compound, NiZn 3 

 occurs, melting at 876° C, distinctly brittle and giving a characteristic 

 blue coloration with dilute nitric acid. One of the series of mixed 

 crystals passes through a transformation point in the solid state. The 

 microsections were etched either with dilute nitric acid, or first 

 electrolytically, suspended as positive pole in water containing a little 

 sulphuric acid, this process being followed by staining with iodine 

 solution. 



Structure of Metals.J — W. Campbell has accumulated much 

 evidence in support of the universally accepted theory of the crystal - 



* Metallurgie, iv. (1907) pp. 617-31, 639-47, 673-82 (44 figs. |. 



t Tom. cit., pp. 781-5(14 figs.). 



t Tom. cit., pp. 801-9, 825-34 (85 photomicrographs). 



