200 PREPARATION OF REAGENTS [CH. VII 



\ 316. Cedar- Wood Oil. — This is used for oil immersion objectives. It is 

 best kept in a bottle like that shown in Fig. 168. This oil is quite thick. 



For penetrating tissues and preparing them for infiltration with paraffin, thick 

 oil is recommended by Lee. The writer has found, however, that any good cedar 

 wood oil gives excellent results in ordinary histological and embryological work. 

 That known as Cedar Wood Oil (Florida) is excellent, also that known as cedar 

 wood oil (true Lebanon). These forms are far less expensive than that used for 

 immersion objectives. The tissues should be thoroughly dehydrated before put- 

 ting them into cedar-wood oil, and the} - should remain until they are transparent 



a 286). 



{! 317. Clarifier, Castor-Xylene Clarifier. — This is composed of castor oil 1 

 part and xylene* 3 parts. (Trans. Amer. Micr. Soc, 1895, p. 361). 



\ 318. Clearing Mixture ( #281, 298). — (A). One of the most satisfactory and 

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

 crystals (Acidnm carbolicum. A. phenicum crystallizatum) 40 cc. with rectified 

 oil of turpentine (Oleum terebinthinae rectification) 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. 



I 319. Collodion. — This is a solution of soluble cottonf or other form of pyroxy- 

 lin in equal parts of sulphuric ether and 95",, alcohol. Two solutions are used : 



*The hydrocarbon xylene (C,H nl ) 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 tetranitrate C, ,H r , ; (N0 3 ) 4 0„, and cellulose pentanitrate, 

 Ci 2 H ls (N0 : ;)-,0-. 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. 



