( IIATTKE IV. 



FOL (Lchrb. <l vergl. mil-. Amtt.. 1884, p. 100) recommends the 



following variant : 



1 per cent, chromic acid . 25 vols. 



1 per cent, osmic acid . . 2 



J per cent, acetic acid . . . 5 ,, 



Water . . . . . . 68 



that i- to say, a mixture much weaker in osmium than Flemming's. 

 A mixture still weaker than this in osmium, viz. with 1 vol. osmic 



a.-i,l solution, instead of 2, has been recommended by Com (Zeit. v:iss. 



Mi H-.. vi. 1890, p. 



SECOND or STRONG formula (Zeit. u-iss. J\Iik., I, 1884, 

 p. 349) : 



1 per cent, chromic acid . .15 parts. 



2 per cent, osmic acid . . 4 ,, 

 Glacial acetic acid . . .1 part. 



If this mixture be kept in stock in large quantities, it 

 may go bad, on account of the large proportion of organic 

 acid contained in it. I therefore recommend that the osmic 

 and chromic acid be kept ready mixed in the proportions 

 given, and 5 per cent, of acetic acid added at the moment of 

 using. 



\VEAKER FORMULA. More recently, FLEMMING has been 

 making up the mixture with only 2 parts of the osmic acid 

 instead of 4, and has spoken of this modification as "weaker 

 osmium mixture ' (MEVES, in EncycL Mikr. Teclm., p. 476). 



MEVES (loc. cit.) takes for delicate objects 15 parts of 

 chromic acid of only 0'5 per cent.,, 2 or 4 of osmic acid of 

 2 per cent., and 1 of acetic acid, and thus gets less 

 shrinkage. 



PODWYSSOZKI recommends (for glands especially) the following modi- 

 fication : 



1 per cent. Cr0 3 dissolved in 0'5 per cent, solution of 

 corrosive sublimate . . . . .15 c.c. 



2 per cent, osmic acid solution . . . .4 c.c. 

 Glacial acetic acid . . . . . 6 to 8 drops. 



The sublimate is said to augment the penetration of the osmium, but 

 is unfavourable to staining (ZiEGLEn's Beitruc/e z. path. Ancit., i, 1886; 

 it. wise. Mik., iii, 1886, p. 405). 



The first or weak liquid is the better for very small 

 objects, the second or strong one for larger ones, as it has 

 lu'lfcr penetration. These liquids may be allowed to act for 

 many hours or days, or according to some workers even 



