244 PRESERVATIVE LIQUIDS. 



degree. In order to facilitate the removal of the cover in 

 this process, the slide may be gently warmed by passing it 

 two or three times through the flame of a spirit lamp. No 

 preparation can be considered to be made secundum artem 

 until every part of the object has been thoroughly impregnated 

 with strong pure glycerin. 



The shrinking that frequently occurs when delicate struc- 

 tures are brought into glycerin may generally be cured by this 

 treatment; cells which at first appear hopelessly collapsed 

 gradually swell out to their normal forms and dimensions. 



For closing glycerin mounts, the edges of the cover should 

 first (after having been cleansed as far as possible from 

 superfluous glycerin) be painted with a layer of glycerin jelly ; 

 as soon as this is set a coat of any of the usual cements may 

 be applied. This has of course been for the last twenty years 

 one of the commonplaces of hisfcological technic, but that 

 has not prevented somebody from recently describing the pro- 

 cess at great length as new. 



Glycerin dissolves carbonate of lime, and is therefore to be 

 rejected in the preparation of calcareous structures that it is 

 wished to preserve. 



The already high index of refraction of glycerin (Price's glycerin, n = 

 1*46) may be raised to about that of crown glass by dissolving suitable sub- 

 stances in the glycerin. Thus the refractive index of a solution of chloride 

 of cadmium (CdCl 2 )* in glycerin may be T504 ; that of a saturated solution 

 of sulphocarbonate of zinc in glycerin may be 1'501 ; that of a saturated 

 solution of Schering'sf chloral hydrate (in crusts) in glycerin is I'olO; that 

 of iodate of zinc in glycerin may be brought up to 1'56.J The clearing 

 action of glycerin may thus be greatly increased, and the full aperture of 

 homogeneous objectives brought to bear on objects mounted in one of the 

 above-named solutions. 



The sulphocarbolate of zinc solution may be prepared by taking equal 

 parts by weight of Price's glycerin and sulphocarbolate of zinc crystals, 

 mingling the two, and applying sufficient heat to boil the glycerin. The 

 solution can be made in about an hour, but no fear need be had about boil- 

 ing too long, as the longer this is done the less liability will there be for the 

 solution to deposit crystals on the bottom of the bottle when cooled, which 

 it will do if the temperature is only kept up long enough to dissolve the 



* Journ. Roy. Mic. Soc., ii, 1879, p. 346. 



f Ibid. (N.S.), i, 1881, p. 943. 



J Ibid., p. 366. 



Ibid., iii, 1880, p. 1051. 



