246 The Philippine Journal of Science isis 



surface of the liquid without undue stirring or agitation. Sev- 

 eral days are required for concentration of the glycerin. Too 

 rapid concentration causes shrinkage of the specimens. Passing 

 the air admitted to the bottle through calcium chloride tubes 

 and a sulphuric acid gas drier does not materially accelerate 

 the evaporation. 



When smaller quantities than 2.5 cc of material are to be 

 treated, the specimens in dilute glycerin are placed in a cylin- 

 drical vial about 23 mm wide and 80 mm deep, which is filled 

 to a depth of about 70 mm. This vial is then placed in the larger 

 bottle so as to stand under the air jet. When used in this way 

 the larger bottles are provided with a floor of paraffin, which 

 is melted and then cooled while the bottle stands on a level sup- 

 port, to give it a flat, level surface. 



The use of an aspirator or aspirator pump for providing the 

 air blast is yet to be tried. 



A METHOD FOR MAKING SEALED GLYCERIN MOUNTS 



Sealing mounts in concentrated or dilute glycerin presents a 

 difficulty that does not occur in the use of aqueous media, which 

 on evaporation leave the cover and slide surfaces dry; namely, 

 the impossibility of securing contact of the cementing medium 

 with glass surfaces which have become coated with a film of 

 the nonvolatile glycerin. And, further, owing to its hygroscopic 

 property, the glycerin takes up atmospheric moisture through 

 the least crevice, expanding, and exuding in damp weather, and 

 evaporates, contracting, and drawing air under the cover, until, 

 after the seasonal changes of several years, slides defectively 

 sealed are likely to become completely dry. This difficulty can be 

 obviated by using a cement which is readily freed from a glycerin 

 coat and providing contact of the cement with the glass surfaces 

 before the glycerin is applied. 



I have made mounts of the larger Volvocaceae, which require 

 considerable space between slide and cover, and these are in 

 good condition after three years. The cement used is an alco- 

 holic solution of shellac. It is applied with a brush. The 

 method will now be described in detail. 



Orange flake shellac is prepared by covering it with 95 per 

 cent alcohol and allowing it to stand for several days. If the 

 resulting solution be too thin it is allowed to evaporate partially ; 

 if too thick more alcohol is added. A camel's hair brush for 

 applying the shellac is inserted in a perforated rubber stopper 

 of a bottle of 95 per cent alcohol, in which it is kept when not 

 in use. 



