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 may be 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 the cover carefully dried and be ringed with glycerin jelly before 

 applying a cement ; by 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. Mic. Soc., 1892, p. 293 ; BEHRENS' Tabellen 

 zum Gebrauch bei mikroskopischen Arbeiten (Bruhn, Braunschweig, 

 1892) ; ROUSSELET, Journ. Quek. Mic. Club, vii, 1898, p. 93 ; and 

 as to the comparative tenacity of divers cements, BEHRENS, Zeit. 

 wiss. Mik., ii, 1885, p. 54, and AUBERT Amer. Mon. Mic. Journ., 

 1885, p. 227 ; Journ. Roy. Mic. Soc., 1886, p. 173. AUBERT places 

 MILLER'S caoutchouc cement at the head of the list, LOVETT'S 

 cement coming halfway down, and zinc white cement at the bottom, 

 with less than one-quarter the tenacity of the caoutchouc cement. 



459. Paraffin. Temporary mounts may be closed with paraffin, 

 or white wax, by applying it with a bent wire, as described 471, 

 and be made more or less permanent by varnishing. 



460. Gelatin Cement (MARSH'S Section-cutting, 2nd ed., p. 104). 

 Take half an ounce of NELSON'S opaque gelatin, soak well in water, 



