— 161 — 



surrounding atmosphere. It is also alleged that while the oil is solidifying 

 the thermometer in the later stages rises with extreme slowness, unless 

 the temperature of the bath is raised by a few degrees above the melting- 

 point of the oil (!). 



While we do not wish to disparage the ripe experience of Mr. Umney, 

 we cannot refrain from expressing our surprise that he should have pro- 

 nounced so censorious a judgment on the value of a constant which in 

 reality has stood the test so excellently for many years that its replacement, 

 for the oils under discussion, by the melting-point standard could only 

 be described as a retrograde step. The melting-point would be less 

 suitable in these cases because the oils in question are not uniform 

 bodies but mixtures, and therefore do not melt suddenly and throughout 

 at a precisely defined point, but first become soft and are only gradually 

 converted into a clear liquid when the heating is continued. The con- 

 sequence of this fact is, of course, that it is impossible to indicate a definite 

 point at which the oil melts; — only a range of temperature can be given. 

 In contradistinction to the above fact, the solidifying-point of the oils 

 is sharply defined and easy to observe. We assume that the method of 

 determination is well-known, and will only observe in passing that at the 

 time we recommended 1 ) for the application of this test an apparatus which 

 has proved itself of great practical value, and which may perhaps be 

 known to Mr. Umney. It is of course necessary to carry out the work 

 under the proper conditions, and especially to cool each oil properly 

 below the solidifying point. The last-named condition is imperative 

 because otherwise the process of solidification proceeds too slowly, and 

 observation is rendered more difficult. But on the other hand the oils 

 must not be cooled too far below the solidifying-point, as in that case 

 the results will be too low. For this reason we have altered our original 

 suggestion of cooling the oils to 10° below the sol. p., and substituted-) 

 for it a recommendation to cool them only to about 5° below sol. p., 

 as experiments with pure anethol had shown that by so doing values of 

 sufficient correctness were obtained. It is advisable to work always in the 

 same manner in order that the various qualities of each separate oil may 

 be estimated from a uniform point of view. We cool down as follows: — 



Anethol to +16° 



Anise oil to + 12° 



Star anise oil to +10° 



Fennel oil to + 3° 

 It would be altogether wrong to cool the oils to different degrees below 

 sol. p. on different occasions; when this is done it is not surprising if 

 no comparable results are obtained. But this is no fault of the method, 



*) Report October 1898, 43. 

 2 ) Report October 19(>1, 9. 



