ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 719 



Turntable Improvements.* — Mr. E. H. Griffith writes : — " Turn 

 a disc of zinc-white cement on the centre of the turntable and when 

 bard, ring with pen and ink. For centering purposes the white 

 centre is of great value. The cement can easily be removed with 

 benzole at any time if desired." 



Cover-glasses in the Tropics. — Mr. J. C. Douglas writes from 

 Calcutta : — " We find it very difficult here to get good cover-glasses ; 

 they rapidly become frosted and worthless. They appear to be of a 

 soft lead glass. Would not a green hard glass be more likely to stand ? 

 If you could give any information as to how to get good covers it 

 would be a great service to many. The glasses commonly arrive 

 unfit for use, so that instructions as to keeping them in spirit, acid, 

 or other medium are useless. I think it probable green covers would 

 stand and be preferable in other ways from the greater resistant 

 powers of the green as compared with the soft glass." 



Mr. T. Curties informs us that repeated complaints from Indian 

 correspondents were referred to Messrs. Chance Brothers who were 

 unable to provide a harder thin glass. They recommended its being 

 packed and kept in lime ; no good result followed the use of this, or of 

 French chalk which was also tried. Both rendered the surface deposit 

 harder than ever and more difficult to remove. The last experiment 

 tried was with clove oil, and this has proved quite successful. Dr. 

 Piaxton of Colombo, who suggested its use, writes : — 



" I think we have hit upon the right mode of preserving cover- 

 glass. I used some yesterday, now two months since it was received, 

 and it was in perfect condition." 



Cover-glass Cement.t — Dr. L. Heydenreich gives the following 

 approximate formula for cover-glass cement : — Amber, 25 parts by 

 weight ; copal, 25 do. ; linseed oil boiled and with addition of man- 

 ganese borate, 50 do. ; oil of lavender, 50 to 60 do. ; artificial cinnabar, 

 40 to 60 do. The following directions are given for preparing the 

 cement in small quantities (one or two pounds). The amber resin 

 finely divided is put into a tall glazed vessel and dissolved by the 

 aid of heat in a sand-bath. When perfectly melted, the linseed oil, 

 previously rai-ed to its boiling-point, is added. When the two 

 are well mixed they are poured back into the vessel in which the oil 

 has been heated. - 25 per cent, manganese borate is added and the 

 whole allowed to boil gently for two hours. When the mixture has 

 cooled down to about 70°, so much oil of lavender is added as will 

 render it of a syrupy consistence. The whole is then put aside for a 

 week or two until it has cleared up. The copal is prepared in a 

 similar manner. The two varnishes are mixed together and then the 

 cinnabar is thoroughly rubbed iu. The cement is then poured into 

 stoppered bottles or collapsible tubes. If the varnish should become 

 too thick, it may be thinned down by working a little ol. lavan- 

 dulae into the quantity required for immediate use. 



Prepared in the above manner and, so to speak, for home con- 



* The Microscope, vi. (1886) p. 83. 



t Zcitschr. f. Wiss Mikr., ii. (1SS5) pp. 333-8. 



