CHAPTER XX. 



CEMENTS AND VARNISHES. 



458. Introduction. Two, or at most three, of the media 

 given below will certainly be found sufficient for all useful 

 purposes. For many years I have used only one cement 

 (BELL'S). I recommend, this both as a cement and varnish; 

 gold size maybe found useful for turning cells ; and MILLER'S 

 caoutchouc cement may be kept for occasions on which the 

 utmost solidity is required. Marine glue is only necessary 

 for making glass cells. 



For the operations of mounting in fluids, and of making 

 cells and ringing, see CARPENTER'S The Microscope. 



CARPENTER lays great stress on the principle that the 

 cements or varnishes used for fluid mounts should always be 

 such as contain no mixture of solid particles, for those that 

 do always become porous after a certain lapse of time. All 

 fluid mounts should have the edges of tJie cover carefully dried 

 and be ringed u'itli glycerin jelly before applying a cement ; 

 ly this means all danger of running in is done away with. 

 See 460 and 461. But no method yet devised will make 

 a glycerine mount absolutely permanent. 



See also AUBERT, The Microscope, xi, 1891, 150, and Journ. 

 Roy. Mic. Soc., 1891, p. 692 ; BECK, The Microscope, xi, 1891, 

 pp. 338, 368, and Journ. Roy. Me. Soc., 1892, p. 293; 

 BEHRENS' Tabcllen zum Gebrauch bei mikroskopischen Arbeiten 

 (Bruhn, Braunschweig, 1892) ; EOUSSELET, Journ. Quek. Mic. 

 Club, vii, 1898, p. 93 ; and as to the comparative tenacity of 

 divers cements, BEHRENS, Zeit iriss. Mik., ii, 1885, p. 54, and 

 AUBERT Amer. Hon. Mic. Journ., 1885, p. 227; Journ. Roy. 

 Mic. Soc., 1886, p. 173. BEHRENS gives the palm to amber 

 varnish ; AUBEUT places MILLER'S caoutchouc cement at the 

 head of the list, LOVETT'S cement coming halfway down, and 



