ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 43:^ 



to centre with it. The centre of the disk is marked. To define any 

 point on the slide the condenser is racked down, and a minute drop of 

 cedar-wood oil — tins^ed with carmine — is placed on the centre of this 

 disk. The condenser is racked up until the oil just touches the slide. 

 This is now removed from the stage, and the point indicated by the 

 oil-drop is marked with a diamond. 



Apparatus for Counting Bacteria and other Cells.* — R. Donald 

 describes an apparatus for liquid measurement l)y drops and applications 

 in counting bacteria and other cells, and in serology. In order to 

 promote drop-measuring in serological and bacteriological work the 

 writer claims to have devised a simple system of producing uniform 

 pipettes, clean and sterile, which deliver uniform drops of any required 

 size from ^ c.cm. down to o-^ ^ c.cm. or less, and has devised also forms of 

 constant pressure apparatus for use with the pipettes. 



The fundamental principle of the method rests on the fact that the 

 size of a drop of any given liquid yielded by a clean pipette is deter- 

 mined by the outer circumference of the pipette at the level where the 

 contact edge of the drop clings round the glass, due allowance being 

 made for the rate at which the liquid is detached and the temperature. 

 For further details of this interesting device, the original should be 

 consulted. 



Metallography, etc. 



Aluminium-vanadium Alloys. t — X. Czako describes the microstruc- 

 ture of a number of aluminium-vanadium alloys. At 1 p.c. vanadium, 

 brilliant crystals appeared, embedded in aluminium. The proportion of 

 the crystals increased with increase of vanadium, the 34 • 5 p.c. alloy was 

 nearly homogeneous. By the action of hydrochloric acid on the 30 p.c. 

 alloy, brilliant crystals containing 37*9 p.c. vanadium were isolated, 

 corresponding closely to the formula AI3Y. In a single crystal, cleavage 

 lines and corrosion figures were seen, the corrosion pits having the same 

 form as the crystals seen in the alloy containing 1 p.c. vanadium. In 

 alloys containing not more than 38 p.c. vanadium no etching was neces- 

 sary ; the great hardness of the crystals relative to the aluminium ren- 

 dering the structure visible upon simple polishing. Beyond this point 

 the alloys were etched either with 50 p.c. nitric acid to which had been 

 added 6 p.c. of chromic acid, or by electrolysis in sodium-chloride solu- 

 tion. Crystals containing 64*8 p.c. vanadium, corresponding to the 

 formula Al Y were also isolated. 



Cadmium-arsenic Alloys. J — S. F. Zemczuzny has investigated the 

 cadmium-arsenic system, and describes the microstructure of numerous. 



* Proc. Ro5\ Soc, Ser. B, Ixxxvi. (1913) pp. 198-202 (2 figs.). 



t Comptes Rendus, clvi. (1913) pp. 140-2 (2 figs.). 



t Int. Zeitschr. Metallographie, iv. (1918) pp. 228-247 (14 figs.). 



