MICROCHEMISTRY. 73 



usually several hours and a gentle warming for complete 

 decolorization. 



It has been shown by the researches of Altmann (I, 106) 

 that this reaction is by no means characteristic of all fats. 

 It is, on the contrary, suppressed in palmitic acid, stearic 

 acid, and their triglycerides, in the mono- and triglycerides 

 of butyrin, in lecithin, jecorin, and soap. But a strong 

 blackening occurs with free oleic acid and olein. These 

 two compounds are distinguished from each other by the 

 fact that, when it is blackened by osmic acid, oleic acid is 

 still soluble in alcohol, while olein is not. 



If tannins be present in the cells to be tested for fatty 

 oils, they should be extracted by boiling with water before 

 the addition of the osmic acid, since they also blacken with 

 it. Ethereal oils can be removed by heating to 130 C. 

 <cf. 145)- 



112. The saponification of fats under the microscope was 

 first carried out by Molisch (I, 10, note). For this purpose 

 he places the sections to be studied in a drop of a mixture 

 of equal parts of a concentrated solution of potassium 

 hydrate and a concentrated solution of ammonia. After 

 half an hour or an hour or an even longer time, the oil- 

 drops, "constantly losing their strong refractive power, 

 harden into myelin-like or botryoidal bodies or into irregu- 

 lar masses (soaps) often consisting wholly of small crystal- 

 needles." 



Different objects seem to behave very differently in this 

 respect. Thus, I obtained very delicate crystal-needles 

 (cf. Fig. 25) on placing sections from 

 the endosperm of the coffee-bean in the 

 above-mentioned mixture of alkalies. 

 These formed, after a few hours, around 

 the oil-drops, which in twenty-four hours 

 were wholly converted into crystals. I 

 observed in places, within the crystal- FIG. 25 .-ou - drops from 



the endosperm of the 



aggregates, a strongly refractive rounded -f/ r % b - n nific fi ^ on h % 

 body, which, as examination by polar- caustic potash and ammo- 

 ized light shows, was a sphaerocrystal, 

 and showed the familiar dark cross, with crossed nicols. 



