CHAPTER V. 



FIXING AND HARDrSNlNG AGENTS. CHLORIDES, ORGANIC 

 S, AND OTI 



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^ in them is partly 

 split up by hydrolysis into CI, 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 j 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. Zuol. 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 



