164 



ODOROGRAPHIA. 



the solidification is accompanied by a disengagement of heat 

 which is sufhcient to raise the temperature from the point at which 

 solidification begins, up to its ordinary or true congealing point. 

 This physical law being applicable to anise oils, Mr. Umney 

 continued to remark that : — " The solidifying points of star-anise 

 oil, hitherto quoted, have been abnormal ones, due to their deter- 

 mination whilst the fluid was at rest. The trioe congealing point 

 is the temperature to which the thermometer immediately rises on 

 the solidification taking place. The ' Pimpinella ' oil does not 

 present such a marked difference in respect to its abnormal and 

 true congealing points, but that of star anise presents a strange 

 dissimilarity." The following table records results of Mr. Umney's 

 investigations : — 



As regards the fact that some liquids, such as Anise, Star Anise 

 and Fennel oils remain liquid when submitted to a temperature 

 many degrees below their normal point of congelation, it has been 

 observed that this phenomenon (sometimes called ''under-cooling") 

 can be readily prevented by adding to the oil to be tested a few 

 ready formed crystals, which can be obtained by first solidifying a 

 small quantity of the oil in a mixture of salt and ice. The process 

 is as follows : — The sample to be tested is cooled to about 12^ or 

 14^ C. by immersion in cold water, and then by means of a glass 

 rod, a trace of crystallized oil is added. The whole mass should 

 now solidify to a crystalline paste which ought not to liquefy under 

 15° C. Care should be taken in making this test, that the contents 



