( 88 ) 



Probably, a case of isomorphotropoiis relation occurs here with 

 the acetates ; both esters are, probably, inonocliiiic, although this is 

 not quite certain for the cholesterol-ester. This is pseudotetragonal and 



according to Von Zepharovich : monoclinic, with /? =r= 73°38' ; 



according to Obermayek: tricUnic, with /^=106^17', «=90°20', y=90°6', 



while the axial relations are 1,85 : 1 : 1,75. 



The phytosterol-ester has been approximately measured microsco- 

 pically by Beykirch and seems to possess a monoclinic or at least a 

 triclinic symmetry with monoclinic limit-value. In my opinion both 

 compounds are certainly not isomorphous. In any case it might be 

 possible that even though a direct isomorphism does not exist in 

 the two ester-series, there are other terms which exhibit isomor- 

 photropous miscibility in an analogous manner, as found for the ace- 

 tates by BöMER. I have extended the research so as to include the 

 isovalerates ; the result however is negative and the case of the 

 acetic esters seems to be the only one in this series. 



The following instance may be quoted : 



31.87o cholesterol-butyrate -f- ()8,27o phytosterol-butyrate indicate 

 for t, 8i; and for t^ 83° etc. etc. 



For the formiates, the lo^vering had been already observed by Bömer; 

 other esters, also those of the iso-acids behave in an analogous 

 manner : at both sides of the melting-diagram occurs a lowering of 

 the initial melting points. It is, however, highly probable that in 

 some, perhaps in all cases, there exists an isor/zmorpholropous mixing 

 with a blank in the series of the mixed crystals. 



The anisotropons liquid phase of cholesterol-esters gives rise in this 

 case to anisotropons liquid mixed crystals. I just wish to observe that 

 for some of the lower-melting esters, such as the bntyrale, capronate, 

 caprinate, normal valerate, etc, the temperature t^ for these mixed 

 crystals may be brought to about 50^ or 60° or lower and this creates 

 an opportunity for studying liquid mixed crystals at such tempera- 

 tures, which greatly facilitates microscopical experiments. 



In all probability, I shall shortly undertake such a study of these 

 substances. Of theoretical importance is also the possibility, to which 

 Prof. Bakhuis Roozeboom called my attention, that in those substances 

 where t^ answers to the more-labile condition, the at tirst more labile 

 liquid mixed crystals, on being mixed with a foreign substance, 

 become, finally, stable in regard to the isotropous fused mass. Expe- 

 riments with these preparations, in this sense, will be undertaken 

 elsewhere. Perhaps, a study of the low-melting derivatives Or else a 

 similar study of the low-melting liquid mixed crystals by means of 

 the ultra-microscope might yield something of importance. 



Zadudam, May 1906. 



