176 PREPARATION OF REAGENTS. \_CH. VII. 



The xylene is much the best substance to use for thinning the balsam. Such 

 xylene balsam, as it is then called, may be used for mounting any object suitable 

 for balsam mounting. The dehydration must be very perfect, however, as xylene 

 is wholly immiscible with water. 



Natural balsam is liable to be slightly acid. This is of advantage for mounting 

 sections stained with carmine or injected with carmin gelatin or Berlin blue gela- 

 tin. For hematoxylin preparations and for fuchsin preparations the acid will cause 

 the color to fade. The balsam may be neutralized by mixing some carbonate of 

 soda with the thinned solution before it is thickened. In a few days all the soda 

 will settle and the clear balsam above will be neutral and may be poured off and 

 thickened. If one mounts carmine or Berlin blue preparations in the neutral bal- 

 sam the blue will fade and the carmine diffuse. 



I 301. Chloroform Paraffin. — This is made by mixing the 4 parts of the paraffin 

 used for imbedding (ji 314) with 1 part of chloroform. This gives a paraffin which 

 melts at a lower temperature than the pure paraffin. If it is kept warm the chloro- 

 form evaporates in 3 to 6 days, leaving pure paraffin. 



\ 302. Clanfler, Castor-Xylene Clarifier. — This is composed of castor oil 1 part 

 and xylene* 3 parts. 



$303. Clearing Mixture (? 266, 282). — (A). One of the most satisfactory and 

 generally applicable clearers is carbol turpentine, made by mixing carbolic acid 

 crystals (Acidum carbolicum. A. phenicum crystalizatum) 40 cc. with rectified 

 oil of turpentine [Oleum terebinthinae rectificatum) 60 cc. If the carbolic acid 

 does not dissolve in the turpentine add 5 cc. of 95% alcohol, or increase the tur- 

 pentine, thus : carbolic acid 30 cc, turpentine 70 cc. 



(B). Carbol-Xylene, Clearer. — Vasale recommends as a clearer, xylene 75 cc, 

 carbolic acid (melted crystals) 25 cc. It is used in the same way as the preceding. 



\ 304. Collodion. — This is a solution of soluble cottonf or other form of pyroxy- 

 lin in equal parts of sulphuric ether and 95% alcohol. Three solutions are used : 



*The hydrocarbon xylene (C 8 H I0 ) is called xylol in German. In English, 

 members of the hydrocarbon series have the termination "ene" while members 

 of the alcohol series terminate in " ol." 



■fThe substance used in preparing collodion goes by various names, soluble cot- 

 ton or collodion cotton is perhaps best. -This is cellulose nitrate, and consists of a 

 mixture of cellulose tetrauitrate C Ia H j6 (N0 3 ) 4 6 , and cellulose pentanitrate, C„ 

 H I5 (N0 3 ) s 5 . Besides the names soluble and collodion cotton, it is called gun 

 cotton and pyroxylin. Pyroxylin is the more general term and includes several 

 of the cellulose nitrates. Celloidin is a patent preparation of pyroxylin, more ex- 

 pensive than soluble cotton, but in no way superior to it for imbedding. 



Soluble cotton should be kept in the dark to avoid decomposition. After it is in 

 solution this decomposition is not so liable to occur. The decomposition of the dry 

 cotton gives rise to nitrous acid, and hence it is best to keep it in a box loosely 

 ■ covered so that the nitrous acid may escape. 



Cellulose nitrate is explosive under concussion and when heated to 150° centi- 

 grade. In the air, the loose soluble cotton burns without explosion. It is said not 

 to injure the hand if held upon it during ignition and that it does not fire gun- 

 powder if burned upon it. So far as known to the writer, no accident has ever 

 occurred from the use of soluble cotton for microscopical purposes. I wish to ex- 

 press my thanks to Professor W. R. Orndorff, organic chemist in Cornell Univer- 

 sity, for the above information. Proc Amer. Micr. Soc, vol. XVII (1895), pp. 

 361-370. 



