ALCOHOL. 39 



57. Picro-hydro chloric Acid (MAYER, Ibid.). Prepared in the same 

 way as picro-sulphuric acid, except that instead of 2 vols. of sulphuric acid 

 you take " 8 vols. of pure hydrochloric acid of 25 per cent. HC1." Mayer 

 now dissolves the picric acid in the hydrochloric acid water, so that the for- 

 mula runs 



Water 100 vols. 



Hydrochloric acid (of 25 per cent. HC1) . . 8 



Picrid acid, as much as will dissolve. 

 The fluid is used undiluted. 

 The properties of this fluid are similar to those of picro-nitric acid. 



58. Picro-chromic Acid. See ante, 41. 



59. Picro-osmic Acid. FLEMMING (Zells. Kern-u.-Zellth., p. 381) has 

 experimented with mixtures made by substituting picric for chromic acid in 

 the chromo-osmic mixtures (ante, 34 and 35). The results are identical 

 so far as regards the fixation (of nuclei) ; but staining is rendered more 

 difficult. 



Other Fixing Agents. 



60. Alcohol. For fixing, only two grades of alcohol are 

 found generally useful very weak alcohol on the one hand, 

 and absolute alcohol on the other hand. Absolute alcohol 

 ranks as a fixing agent because it kills and hardens with such 

 rapidity that structures have not time to get deformed in the 

 process by the energetic dehydration that unavoidably takes 

 place. Dilute alcohol ranks as a fixing agent in virtue of 

 being of such a strength as to possess a sufficiently energetic 

 coagulating action and yet contains enough water to have but 

 a feeble and innocuous dehydrating action. The intermediate 

 grades do not realise these conditions, and therefore should 

 not be employed alone for fixing. But they may be very 

 useful in combination with other fixing agents (such as corro- 

 sive sublimate, chromic acid or nitric acid) by greatly enhanc- 

 ing their penetrating power ; 70 per cent, is a good grade for 

 this purpose. 



61. One-third Alcohol. The one grade of weak alcohol that 

 is found generally useful for fixing is one-third alcohol, or 

 RANVIER'S ALCOHOL, known in France as " Alcohol au tiers," 

 which is the name given to it by Ranvier himself ; in Germany 

 as " Drittelalcohol " or " Ranviersche alcohol dilutus ;" in 

 Italy, as " alcool al terzo." In consists of two parts of water 

 and one part of alcohol of 36 Baume. Now, since alcohol of 

 36 Baume contains nearly 89*6 per cent, of absolute alcohol, it 



