58 FIXING AND HARDENING AGENTS. 



portant one. 90 to 95 per cent, is the most generally useful strength. 

 Weaker alcohol, down to 70 per cent., is often indicated. Absolute 

 alcohol is seldom advisable. You ought to begin with weak, and 

 proceed gradually to stronger, alcohol. Large quantities of alcohol 

 should be taken. The alcohol should be frequently changed, or the 

 tissue should be suspended near the top of it ( 34). Many weeks 

 may be necessary for hardening large specimens. Small pieces of 

 permeable tissue, such as mucous membrane, may be sufficiently 

 hardened in twenty-four hours. 



103. Absolute Alcohol. This is sometimes valuable on account 

 of its great penetrating power. Mayer finds that boiling absolute 

 alcohol is often the only means of killing certain Arthropoda rapidly 

 enough to avoid maceration. 



It is important to employ for fixing a very large proportion of 

 alcohol. Alum-carmine is a good stain for small specimens so fixed. 

 For preservation, the object should be put into a weaker alcohol, 

 90 per cent, or less. 



As to the supposed superiority of absolute alcohol over ordinary 

 strong alcohol, see last ; and amongst authors upholding its superiority, 

 see besides KANVIER, MAYER (Mitth. Zool. Stat. Neapel, ii, 1880, p. 7) ; 

 BRUEL (Zool. Jahrb., Abth. Morph., x, 1897, p. 569); and VAN EEES 

 (ibid., iii, 1888, p. 10). 



Absolute alcohol is a product that it is almost impossible to preserve 

 in use, on account of the rapidity with which it hydrates 011 exposure to 

 air. Fol recommends that a little quicklime be kept in it. This absorbs 

 part at least of the moisture drawn by it from the air. 



Ranvier prepares a sufficiently " absolute " alcohol as follows : 

 Strong (95 per cent.) alcohol is treated with calcined cupric sulphate, 

 with which it is shaken up and allowed to remain for a day or two. It 

 is then decanted and treated with fresh cupric sulphate, and the 

 operation is repeated until the fresh cupric sulphate no longer becomes 

 conspicuously blue on contact with the alcohol ; or until, on a drop of 

 the alcohol being mixed with a drop of turpentine, no particles of water 

 can be seen in it under the microscope. The cupric sulphate is prepared 

 by calcining common blue vitriol in a porcelain capsule over a flame 

 until it becomes white, and then reducing it to powder (see Proc. Acad. 

 Nat. Sci. Philad., 1884, p. 27 ; Journ. Eoy. Mic. Soc., 1884, pp. 322 and 

 984). 



Test for the presence of water (YvON, G. R. Acad. Sci., 1897, p. 1181). 

 Add coarsely powdered calcium carbide ; the merest trace of water will 

 cause an evolution of acetylene gas, and on agitation the alcohol will 

 become turbid. 



104. One-third Alcohol. The grade of weak alcohol that is 

 generally held to be most useful for fixing is one-third alcohol, or 

 RANVIER'S ALCOHOL. It consivsts of two parts of water and one part 



