204 PREPARATION OF REAGENTS \CH. VII 



funnel (§ 315), into an open dish or a wide-mouth bottle. To every 100 cc. of 

 this filtered shellac, 2 cc. of castor oil and 2 cc. of Venetian turpentine are added 

 to render the shellac less brittle. The filtered shellac will be too thin, and must 

 be allowed to evaporate till it is of the consistency of thin syrup. It is then put 

 into a capped bottle, and for use, into a small spirit lamp (Fig, 153). In case the 

 cement gets too thick add a small amount of 95% alcohol or some thin shellac. 

 The solution of shellac almost always remains muddy, and in most cases it takes a 

 very long time for the flocculent substance to settle. One can very quickly obtain a 

 clear solution as follows : When the shellac has had time to thoroughly dissolve, 

 i. f., in a week or two in a warm place, or in less time if the bottle is frequently 

 shaken, a part of the dissolved shellac is poured into a bottle and about one-fourth 

 as much gasolin or benzin added and the two well shaken. After twenty-four 

 hours or so the flocculent, undissolved substance will separate from the shellac so- 

 lution and rise with the gasolin to the top. The clear solution may then be siphoned 

 off or drawn off from the bottom if one has an aspirating bottle. (R. Hitchcock, 

 Amer. Monthly Micr. Jour , July, 1884, p. 131). 



If one desires to color the shellac, the addition of a strong alcoholic solution 

 of some of the coal tar colors is good, but it is liable to dissolve in the mounting 

 medium when shellac is used for sealing. A small amount of lampblack well 

 rubbed up in very thin shellac and filtered, is good to darken the shellac. 



ARRANGING AND MOUNTING MINUTE OBJECTS 



\ 335. Minute objects like diatoms or the scales of insects may be arranged in 

 geometrical figures or in some fanciful way, either for ornament or more satisfac- 

 tory study. To do this the cover-glass is placed over the guide. This guide for 

 geometrical figures may be a net-micrometer or a series of concentric circles. In 

 order that the objects may remain in place, however, they must be fastened to the 

 cover-glass. As an adhesive substance, mucilage or liquid gelatin (£ 329) thinned 

 with an equal volume of 50% acetic acid answers well. A very thin coating of this is 

 spread on the cover with a needle, or in some other way and allowed to dry. The ob- 

 jects are then placed on the gelatinized side of the cover and carefully got into posi- 

 tion with a mechanical finger, made by fastening a cat's whisker in a needle holder. 

 For most of these objects a simple microscope with stand (Figs. 20, 145, 146) will be 

 found of great advantage. After the objects are arranged, one breathes very gently 

 on the cover-glass to soften the mucilage or gelatin. It is then allowed to dry and 

 if a suitable amount of gelatin has been used, and it has been properly moistened, 

 the objects will be found firmly anchored. In mounting one may use Canada bal- 

 sam or mount dry on a cell {\ 247, 255). See Newcomer, Amer. Micr. Soc.'s Proc, 

 1886, p. 128 ; see also E. H. Griffith and H. L. Smith, Amer. Jour, of Micros., iv, 

 102, v, S7 ; Amer. Monthly Micr. Jour., i, 66. 107, 113. Cunningham, The Micro- 

 scope, viii, 1888, p. 237. 



For additional apparatus for this chapter, see Ch. X. 



