670 MICROCHEMICAL TESTS 



1891). Place sections in a drop of a mixture of equal parts concen- 

 trated KOH solution and concentrated ammonia solution. After half 

 an hour to one hour or more the oil-drops, which steadily become less 

 refractive, harden into myelin-like or botryoidal bodies or into irre- 

 gular masses (soaps) often consisting wholly of small crystal-needles. 

 See also Eckerson, Fats (McClung's Micr. Tech., p. 160) ; Michaelis, 

 Fat (Krause's Encyklopddie Mikr. Tech., Berlin, 1926) ; Ciaccio, 

 Pathologica, xiii, 1921, p. 183 ; Czapek, Ber. Deut. hot. Ges., xxxvii, 1919 

 p. 207 (lipoids). 



1347. Waxes. See de Bary {Bot Zeitg., 1871, p. 132). They 

 are insoluble in water and melt together into drops in hot water. 

 Insoluble or nearly so in cold alcohol, soluble in hot alcohol. 

 On heating in a solution of alkannin in 50 per cent, alcohol, they 

 run together into red drops. 



1348. Sugars. Molisch {Sitzungsber. Akad. Wiss. Wien., 

 xciiij 1886, p. 912) finds the two following reactions common to 

 many carbohydrates : (1) Add a drop of 15 to 20 per cent, alcoholic 

 a-naphthol solution and then 2 to 3 drops concentrated sulphuric 

 acid ; a violet colour results. (2) Thymol used in the same way 

 gives a carmine-red colour. 



The reduction of copper salts by sugars in the presence of 

 excess alkali is generally employed. But this reaction is unsatis- 

 factory because of the considerable diffusion that occurs and 

 because sucrose, if suspected, must first be hydrolysed by boiling 

 with acid. 



The best results have been secured by Mangham {New Phyt., 

 X, 1911, p. 160 ; Ann. Bot., xxix, 1915, p. 369) and others using 

 the osazone test first introduced by Senft {Siiz. Akad. Wiss., 

 cxiii, 1904, p. 3 ; Bot. Centrbl, 1904, p. 28). It is very delicate, 

 giving glucose, for instance, in 0-015 per cent, solution. But it is 

 comparatively slow. Two solutions are used : (1) 1 grm. phenyl- 

 hydrazine hydrochloride in 10 grm. of glycerin, and (2) 1 grm. 

 sodium acetate in 10 grm. glycerin. Aid the solution by heating, 

 if necessary, and filter before use. Glycerin is used because it is 

 more penetrating than water and also will not evaporate and 

 deposit crystals of the substances used. It must be pure, for 

 commercial glycerin is often adulterated with sugars. The 

 glycerin retards crystal formation, the preparations therefore 

 cannot be used for some time. Mix 1 drop of each solution on a 

 slide, add a section (which must be at least one cell thick) and a 

 coverslip. Heat on a water bath in a water- jacketed oven for 

 about half an hour, allow to cool and seal with a mixture of gum 

 mastic and paraffin wax ; the osazone crystals will form in varying 

 degrees of rapidity. Compare with the osazones given by solutions 

 of known sugars. 



Methylphenylhydrazine gives a crystalline osazone with levu- 

 lose but not with dextrose. 



1349. Starch. The most characteristic test is the blue reaction 



