Ch. X] REAGENTS AND THEIR PREPARATION 353 



crystals (Acidcum carbolicum. A. plicnicum crystallizatum) 40 cc. 

 with rectified oil of turpentine {Oleum terebinthinae redijicathini) 

 60 cc. If the carbolic acid does not dissolve in the turpentine, 

 increase the turpentine, thus: carbolic acid 30 cc, turpentine 70 cc. 



This clearer is not so good as the preceding for mounting objects 

 which have been stained with osmic acid, as the hydrogen dioxid 

 (H2O2) present fades the blackened osmic acid. 



§ 554. Clarifier, castor-xylene clarifier. — This is composed of castor 

 oil 1 part and xylene 3 parts. (Trans. Amer. Micr. Soc, 1895, p. 361.) 

 For the use of this clarifier, see under the collodion method, (§ 635). 



§ 555. Collodion. — This is a solution of soluble cotton or other 

 form of pyroxylin in equal parts of sulphuric ether in 95 % or absolute 

 alcohol. In using soluble cotton for infiltrating and imbedding tissues 

 several different strengths are used, commencing with weak and pro- 

 ceeding to strong mixtures. The last in which the tissue is imbedded 

 is as thick a solution as can be made. All collodion solutions should 

 be kept well corked, for the ether and alcohol are very volatile. 



§555a. — The substance used in preparing collodion goes by various names, 

 soluble cotton or collodion cotton is perhaps best. This is cellulose nitrate, and 

 consists of a mixture of cellulose tetranitrate Ci2Hi 6 (N0 3 )40c and cellulose pentani- 

 trate, C^H^NC^oOs. 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 

 expensive than soluble cotton. 



An American product known as " parlodion " has recently (1915) appeared 

 to take the place of the celloidin not now obtainable. It is non-explosive, and 

 said to be a very pure, concentrated form of collodion especially adapted to 

 the needs of histology and embryology. (Advertising pages, Anatomical 

 Record, Dec, 1915.) 



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 decomposi- 

 tion of the 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° 

 centigrade. 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 gunpowder if burned upon it. So far as known to the writer, no acci- 

 dent has ever occurred from the use of soluble cotton for microscopic pur- 

 poses. I wish to express my thanks to Professor W. R. Orndorff, organic 

 chemist in Cornell University, for the above information. (Proc. Amer. Micr. 

 Soc, vol. XVII (1895), pp. 361-370.) 



§ 556. Collodion for cementing sections to the slide. — This is 

 a f% solution made by adding f gram of soluble cotton to 50 cc. of 



