CH. VII ] PREP A RA TION OF RE A GENTS 1 99 



cooling a part will crystallize out, leaving a cold saturated solution). The satu- 

 rated solution may be used but, if a half saturated solution is employed, it will 

 answer all the purposes. For a half saturated solution take 100 cc. of water, and 

 100 cc. of saturated alum water and mix the two. In case preparations are to be 

 kept some time in alum water, 2% of chloral hydrate should be added to prevent 

 mold. 



\ 315. Balsam, Canada Balsam, Balsam of Fir; Xvlene Balsam. This is 

 one of the oldest and most satisfactory of the resinous media used for mounting 

 microscopical preparations. 



The natural balsam is most often used, but within the last ten years the belief 

 has arisen that it is better to evaporate the balsam and then dissolve it in xylene 

 or benzole. It certainly dries out more rapidly if so treated. Natural balsam has 

 the advantage of being able to take up a small amount of water so that if sections 

 are not quite dehydrated they will clear up after a time. If xylene balsam is used 

 the dehydration must be almost complete or the preparation will look cloudy. 



Filtering Balsam. Balsam is now furnished already filtered through filter 

 paper. If one wishes to filter it himself a hot filter like that shown in Fig. 155 is 

 good. If xylene balsam is used it may be made thin and filtered without heat. 

 For filtering balsam and all resinous and gummy materials, the writer has found a 

 paper funnel the most satisfactory. It can be used once and then thrown away. 

 Such a funnel may be easily made by rolling a sheet of thick writing paper 

 in the form of a cone and cementing the paper where it overlaps, or winding a 

 string several times around the lower part. Such a funnel is best used in one of 

 the rings for holding funnels. 



FIG. 1 68. Vessel for homogeneous immersion liquid 

 (thick cedar-wood oil}. This is jilled only a little above the 

 lower end of the inner tube. The oil will not then run out if 

 the vessel is tipped over. For applying the oil there is a wire 

 loop attached to the upper cork. The side cork is for the pur- 

 pose of emptying the bottle, and also for the escape of the air 

 when filling it. ( The Spencer Lens Co.; see also Zeit. 

 wiss. Mikr. , /&?7, p. 348, and Jour. Roy. Micr. Soc. , 1898, 

 p. 238}. 



Natural Balsam. All the samples of balsam tested by the author have been 

 found slightly acid. This is an advantage for carmine, and acid fuchsin stains or 

 any other acid stain. Also for preparations injected with carmine or Berlin blue. 

 In these cases the color would fade or diffuse if the medium were not slightly 

 acid. For hematoxylin the acid is detrimental. For example, the slight amount 

 of acid in the balsam will cause the delicate stain in the finest fibers of Weigert 

 preparations to fade. Also the fuchsin and other stains which are faded by acids. 

 To neutralize the balsam add some pure sodium carbonate, set the balsam in a 

 warm place and shake it occassionally. After a month or so the soda will settle 

 and the clear supernatant balsam will be found very slightly alkaline. Use this 

 whenever an acid medium would fade the stain in the specimen. 



