ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



2G7 



1 part mercuric chloride to every 5000 parts of water. On removal the 

 hides are drained, and then transferred to a pit containing a saturated 

 solution of common salt for about one hour, after which they are 

 drained. For goat- and sheep-skins the quantity of formic- acid is less. 



Self-regulating Siphon.* — W. H. Tait describes a self-regulating 

 siphon which is simple in construction and very efficient in use. The 

 U-tube bent out of ordinary ^-in. quill tubing, as shown in the 

 illustration (fig. 42), is narrowed at the point A, and the small piece of 

 glass rod C is drawn out so as to fit this constriction. The bulb B, 

 sealed on to the top of this rod, 

 floats on the surface of the water. The 

 U-tube must be so fixed, that when 

 the water is at the desired level the rod 

 just fits into A, and so closes the exit. 

 If the level of the water in the vessel 

 D rises at all, the bulb is raised and 

 the excess of water flows out through 

 the siphon. A useful apparatus for 

 laboratories when it is required to keep 

 a continuous flow of water through a 

 vessel in which the level must remain 

 constant. 



Filtering by Aid of the Centri- 

 fuge.f — R. Sabouraud and A. Vernes 

 state that the difficulties of filtration 

 are easily overcome by means of a cen- 

 trifuge. They place porcelain bougie 

 filters in the cups or buckets of a cen- 

 trifuge ; presumably within some glass 

 vessel, as the authors remark that the 

 apparatus is easily sterilizable. The 

 bougies will stand 0000 revolutions a 

 minute without breaking, and filtra- 

 tion is effected in a few minutes. For 

 filtering organic fluids, a collodion sac 

 is easily made by coating the internal 

 surface of the bougie with collodion. 



Polishing Metallic Preparations for Microscopical Examination.^ 

 In the final polishing of delicate metallic specimens for microscopic 

 examination, it has been found impossible entirely to obliterate the 

 scratches without destroying crystalline structure. If, however, the 

 following methods are adopted, there will be few, if any, objectionable 

 marks visible under a power of less than 800 to 1000 diameters, and all 

 the perfection of structure will be preserved. After polishing with 



• Nature, lxxxvi. (1911) p. 45 (1 fig.). 



t C.R. Soc. Biol. Paris, lxix. (1910) pp. 620-1. 



j Communicated by John Mastin, F.R.M.S. 



Fig. 42. 



