CHAPTER V. 



FIXING AND HARDENING AGENTS. CHLORIDES, ORGANIC 

 ACIDS, AND OTHERS. 



Chlorides. 



63. Bichloride of Mercury (Corrosive Sublimate). Corrosive 

 sublimate is soluble in about sixteen parts of cold and three 

 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 (tJgCl) 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 g. sublimate, 3 g. glacial acetic acid, and 300 g. 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 (Mitth. 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 



