CHLORIDES ORGANIC ACIDS ETC. 63 



104. Picro-chromic Acid (Fol, Lehrb., p. 100). 



Picric acid, sol. sat. in water . . 10 vols. 



1 per cent, chromic acid solution . . 25 „ 



Water 65 „ 



We have seen Fol's formula, with the addition of a trace of acetic acid, 

 quoted as " liquid of Haensel." 



Lo Bianco takes equal parts of picro-sulphuric acid and chromic acid 

 of 1 per cent. 



Rawitz {Leitfaden, 1895, p. 24) takes 1 part of picro-nitric acid, 

 and 4 parts 1 per cent, chromic acid. Wash out in 70 per cent, 

 alcohol. 



105. 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 (§ 47), and finds the results identical, 

 so far as regards the fixation of nuclei. The fixation of cytoplasm is in 

 Lee's preparations decidedly inferior. 



O. VOM Rath (Anat. Anz., xi, 1895, p. 289) adds to 200 c.c. of saturated 

 aqueous solution of picric acid, 12 c.c. of 2 per cent, solution of osmic 

 acid, and 2 c.c. of glacial acetic acid. 



Rawitz {Leitfaden, p. 24) takes picro-nitric acid, 6 vols. ; 2 per cent, 

 osmic acid, 1 vol. Fix for half to three hours. Transfer direct to 70 per 

 cent, alcohol. 



106. Picro-platinic and Picro-platin-osmic Mixtures. O. vom Rath 

 {loc. cit., last §, pp. 282, 285) makes a picro-platinic mixture with 

 200 c.c. saturated aqueous solution of picric acid, 1 grm. of platinic 

 chloride (dissolved in 10 c.c. of water), and 2 c.c. of glacial acetic acid. 



The picro-platin-osmic mixture, which is, in Lee's opinion, much 

 superior, is made by adding to the foregoing 25 c.c. of 2 per cent, osmic 

 acid. 



Other Picric Mixtures, See §§ 115 and 117. 



OTHER FIXING AND HARDENING AGENTS 



107. Ethyl Alcohol. For fixing only two grades of alcohol 

 should be employed — very weak, or absolute. Absolute alcohol 

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

 rapidity that structures have hardly time to get deformed in the 

 process ; very weak, because it possesses a sufficiently energetic 

 coagulating action and yet contains enough water to have but a 

 feeble 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 by enhancing their penetrating power ; 70 per cent, 

 is a good grade for this purpose. 



Table for diluting alcohol (after Gay-Lussac). To use this table, find 

 in the upper horizontal row of figures the percentage of the alcohol that 

 it is desired to dilute, and in the vertical row to the left the percentage 

 of the alcohol it is desired to arrive at. Then follow out the vertical 

 and horizontal rows headed respectively by these figures, and the figure 

 printed at the point of intersection of the two rows will show how many 



