72 CHAPTER V. 



certain Arthropoda rapidly enough, to avoid maceration 

 brought about by the slowness of penetration of common 

 cold alcohol (especially in the case of Tracheata) . 



It is important to employ for fixing a very large propor- 

 tion 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 99 ; and amongst authors 

 upholding its superiority, see besides RANVHR, MAYEI: (Mitth. 

 Zool. Stat. Neapel, ii, 1880, p. 7) ; BEUEL (ZuoL Juhrl>., Altli. 

 Morph., Bd. x, 1897, p. 509) ; also VAN REES (ibid., Bd. iii, 

 1888, p. 10). 



Absolute alcohol is found in commerce. It is a product that it is almost 

 impossible to preserve in use, on account of the rapidity with which it 

 hydrates on exposure to air. Fol recommends that a little quicklime be 

 kept in it. This absorbs part at least of the moisture drawn by the alcohol 

 from the air, and has the further advantage of neutralising the acid that is 

 frequently present in commercial alcohol. 



Another plan that I have seen recommended is to suspend strips of gelatin 

 in it. It is stated that by this means ordinary alcohol may be rendered 

 absolute. But then it is probably also rendered very acid thereby. 



Ranvier adopts the following plan for preparing an alcohol absolute 

 enough for all practical purposes. 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 pre- 

 pared by calcining common blue vitriol in a porcelain capsule over a spirit 

 lamp or gas burner until it becomes white, and then reducing it to powder 

 (see Proc. Acacl. Nat. Sci. Philad., 1884, p. 27 ; Science Record, ii, 1884, 

 p. 65 ; Journ. Roy. Mic. Soc. (N. S.), iv, 1884, pp. 322 and 984). 



102. Hydrochloric Acid Alcohol (PAUL MAYEK, Milth. Zool. Stat. 

 Neapel, ii, 1881, p. 7). To 97 vols. of 90 per cent, alcohol, in which is 

 dissolved a small quantity of picric acid, add 3 vols. pure hydrochloric acid. 

 Leave the specimens in the mixture only just long enough to ensure that 

 they are thoroughly penetrated by it. Wash out with 90 per cent, alcohol, 

 the disappearance of the yellow stain of the picric acid being a sign that all 

 the acid is removed. 



The use of this mixture is for the preparation of coarse objects it is in- 

 tended to preserve in alcohol. The object of the acid is to prevent both 

 that glueing together of organs by the perivisceral liquid, which is often 



