PRIMARY FIXATIVES: COAGULANTS 93 



ness on mixture with benzene and does not produce gas (acetylene) 

 on contact with calcium carbide. Ethanol is a powerful dehydrating 

 agent. 



Ionization. Not ionized. 



Oxidation-potential. Ethanol at 95% shows an oxidation- 

 potential of 0*45 volt.^^^ Of the eight fixatives considered in this 

 chapter and the next, only formaldehyde shows a lower potential. 



Manufacture. It is usually prepared from malt or molasses by the 

 action of yeast, with subsequent distillation. Fractional distillation 

 does not give a higher concentration than 95%. Distillation of this 

 strong ethanol at 81° C in the presence of anhydrous calcium 

 sulphate or some other suitable dehydrating agent will give 

 ethanol at 99-95%. 



Ethanol is azeotropic with benzene: that is to say, it forms wdth 

 benzene a binary mixture W'ith sharp boiling-point (68° C). It also 

 forms a ternary azeotropic mixture with benzene and water, with 

 even lower boiling-point (65° C). If benzene is added to ethanol 

 containing some water and the mixture is distilled, the ternary 

 mixture comes off first, then the binary: nearly pure ethanol is left 

 behind, slightly contaminated with benzene. The latter can be 

 removed by filtering through active charcoal. It is called 'azeo- 

 tropic' ethanol, though actually it consists of that fraction of the 

 ethanol that did not form an azeotropic mixture. 



Introduction as fixative. Wine was used in embalming by the 

 ancient Egyptians, but not as the principal preservative. Ethanol 

 appears to have been first used as a preservative for specifically 

 anatomical purposes by Robert Boyle at Oxford in 1663.^^^ The 

 use of spirits of wine for the preservation of animals was well 

 established before the middle of the eighteenth century. It was the 

 examination of a spirit-specimen of Alcyonium, collected by 

 Bernard de Jussieu on the coast of Normandy, that convinced 

 Reaumur that this and other zoophytes were in fact animals, ^^^ 

 and Reaumur himself *^* subsequently recommended the use of 

 the same fluid for the preservation of birds. Henry Baker ^^ preserved 

 hydra in spirits of wine, but subsequently allowed his specimens 

 to dry. The special virtue of ethanol when mixed with acetic acid 

 was discovered by Clarke ^^^ in 185 1. 



Reactions with proteins. Ethanol is a non-additive, coagulant 

 fixative. Coagulates are digestible by pepsin and typsin. In denatur- 

 ing proteins it shifts their iso-electric points less than other fixatives 

 do. Its capacity to denature is much affected by temperature: there 



