(81 ) 



an adhesive by-product which it is (lil'ticiilt to remove. The choles- 

 terol-esters gi\e much nicer crystals; the formiate, acetate and hen- 

 zoate have been measured macroscopically ; the other derivatives 

 crystallise in delicate needles or very thin scaly crystals which are 

 not measurable ; I hope yet to be able to obtain the butyrate in a 

 measurable form '). Iji the case of the caprylate, liic purification was 

 much assisted by the great tendency of the product to crystallise. 

 The purification of the capric ester was, however, much more diffi- 

 cult ; at last, this has also been obtained in a pure state even in 

 beautiful, colourless, plate-shaped crystals, from boiling ligroïn ^). 



The phytosterol-esters retain their white colour on exposure to the 

 light; the cholesterol-esters gradually turn yellowish but may be 

 bleached again by recrystallisation. 



The determination of the melting points, and in the case of the 

 cholesterol-esters, also that of the transition-temperatures: solid — ^ 

 anisotropous-liquid, was always executed in such manner, that the 

 thermometer was placed in the substance, whick entirely surrounded 

 the mercury-reservoir. Not having at my disposal a thermostat, I 

 have not used the graphic construction of the cooling-curve, in 

 the determinations, but simply determined the temperature at wiiich 

 the new phases first occur when the outer bath gets gradually warmer. 



As regards the analysis of the esters, nothing or little can be 

 learned from an elementary analysis in this case, where the formulae 

 of cholesterol and phytoslerol are still doubtful, and where the 

 molecules contain from 28 to 37 carbon-atoms. I have therefore 

 rested content with saponifying a small quantity of the esters with 

 alcoholic potassium hydroxide, which each time liberated the cholesterol 

 or phytosterol with the known melting points. On acidifying the 

 alkaline solution with hydrochloric acid, the fatty acids could be 

 identified by their characteristic odour. 



The esters were called pure, when the melting points, and in the 

 case of cholesterol-esters, botli temperatures, remaijied constant on 

 further recrvstallisation . 



1) I have even succeeded lately in obtaining the formiate in large transparent 

 crystals from a mixture of ligroïn, ethyl acetate and a little alcohol. 



2) The crystals of the cajjrinate are long, flat needles. They form monoclinic 

 individuals, which are elongated parallel to tlie ö-axis, and (latlcned towards |Ü01| 

 The angle |3 is 88° a 89°; there are also the forms: jlOUJ and jToij; measured: 

 (1U0):(101) = ±20.°. The optic axial plane is |01ü|; inclined dispersion: p>v 

 round the first bissectria. Negative double refraction. On jOOlj there is one optical 

 axis visible about the limits of the held. The crystals are cnrvc(l|il;iii( . 



Proceedings Royal Acad. Amsterdam. Vol. IX. 



