( 80 ) 



traversed by a dark cross, so that the whole conveys tlie impression 

 of adjacent interference images of monaxial crystals, viewed perpen- 

 dicularly to the axis and without circular polarisation. The charac- 

 ter of the apparently simple crj'stals is optically negative. 



Cliolesterol, however, presents a quite diiferent image. When melted 



on an object-glass, the substance 

 contracts and forms small droplets, 

 wdiich are scattered sporadically and, 

 on soliditication, look like little nug- 

 gets with scaly edges, wliich mostly 

 exhibit the white of the higher order. 

 That the microscopical distinction 

 in this manner is much safer than 

 by Mügge's method, may be seen from 

 fig. 3 where phytosterol and choleste- 

 rol are represented as seen under the 

 l-'ig- 3- microscope, after being crystallised 



Pliytosterol and Gholeslerol fiom from alcohol. ^4 is cholesterol, B phy- 

 950/0 Alcoliol. tosterol. 



§ 3. Of the fatty esters, I have prepared the acetates, propionates, 

 hutyrates and isobiity rates by heating the two alcohols with the pure 

 acid-anhydride in a reflux apparatus. A two or three hours heating 

 with a small flame, and in the case of the cholesterol, preferably in 

 a dark room, gives a very good yield. When cold, the mass was 

 freed from excess of acid by means of sodinm hydrocarbonate, and 

 then recrystallised from alcohol -{- ether, afterwards from ethyl 

 acetate -f- ligroin, or a mixture of acetone and ligroin, until the nielt- 

 ingpoint was constant. Generally, I nsed equal parts by weight of 

 the alcohol and the acidan hydride. 



The fonniates, valerates, isovalerates, capronates, capnjlates and 

 caprinates were prepared \)\ means of the pure anhydrous acids. 

 These (valeric, caprylic and capric acids) were prepared synthetically 

 by Kahlbau:\[ ; the isovaleric acid and also the anhydrous formic 

 acid were sold commercially as pure acids "Kahlhau.m". Generally, 

 a six hours heating of the alcohol witii a Httle more than its own 

 weight of the acid sufficed to obtain a fairly good yield. Owing, 

 however, to the many recrystallisations required the loss in substance 

 is nnich greater than with the above described method of preparing. 



Both series of esters crystallise well. The phytosterol-esters in soft, 

 flexible, glittering scales ; the formiate and the valerates present some 

 difiiculties in the crystallisation, as they obstinately retain a trace of 



