CHAPTER V. 



FIXING AND HARDENING AGENTS CHLORIDES, ORGANIC ACIDS, 

 AND OTHERS. 



Chlorides. 



63. Bichloride of Mercury (Corrosive Sublimate). Corrosive 

 sublimate is soluble in about 16 parts of cold and 3 of 

 boiling distilled water. It is more soluble in alcohol (1:3) or in 

 ether (1:4) than in water. Its solubility in all these menstrua is 

 augmented by the addition of hydrochloric acid, ammonious chloride, 

 or camphor. With sodium chloride it forms a more easily soluble 

 double salt ; hence sea- water may dissolve over 15 per cent. 



The simple aqueous solutions should always be made with distilled 

 not spring water. The HgCl 2 in them is partly split up by 

 hydrolysis into Cl, H, and (HgCl) 2 , or HgClOH (see Chem. Centralb., 

 1904, i, p. 571 ; the statements of MANN [Methods, pp. 22, 77] are 

 incorrect). These solutions should give an acid reaction with 

 litmus paper, whilst those made with strong sodium chloride solution 

 are neutral. 



For fixing, corrosive sublimate may be used pure ; but in most 

 cases a finer fixation will be obtained if it be acidified with acetic 

 acid, say about 1 per cent, of the glacial acid. I find that a saturated 

 solution in 5 per cent, glacial acetic acid is a very good formula for 

 marine animals ; for others I should take the acid weaker. KAISER'S 

 solution consists of 10 grms. sublimate, 3 c.c. glacial acetic acid, 

 and 300 c.c. distilled water (from Zeit. wiss. Mik., xi, p. 378). 

 VAN BENEDEN has used a saturated solution in 25 per cent, acetic 

 acid, and Lo BIANCO (Mitih. Zool Stat. Neapel, ix, 1890, p. 443). 

 a mixture of 2 parts saturated solution with 1 part of 49 per cent, 

 acetic acid. 



It is sometimes advisable to take the most concentrated solution 

 obtainable. For some very contractile forms (coral polypes, 

 Planaria), a concentrated solution in warm or even boiling water 

 should be employed. For Arthropoda alcoholic solutions are 

 frequently indicated. Delicate objects, however, may require 

 treatment with weak solutions. 



