592 REPORT— 1903. 



form to the other was seen to be in progress, and after an interval of only three 

 hours the absorption band of the enolic ester had almost entirely disappeared. 

 In three weeks the transformation had become complete, as was shown by the 

 molecular vibration curve of the a ester being almost exactly coincident with 

 that of the /3 and y forms. 



Another interesting example is afforded by the study of phloroglucinol, it 

 being a substance with a constitution of a somewhat doubtful character, for owing 

 to the ambiguity of its behaviour towards chemical reagents it is impossible to 

 arrive at a decision from chemical evidence whether the oxygen atoms are present 

 in enolic or ketonic groups. Towards some substances it behaves as a phenol, 

 towards others as a ketone. The doubt also presented itself as to whether phloro- 

 glucinol from various sources had the same constitution, and, further, whether 

 there might not be two isomeric forms of the compound present in equal pro- 

 portions in a solution of the substance. Specimens of phloroglucinol prepared in 

 five different ways from different materials gave curves of molecular vibrations 

 which were identical : this decided the question absolutely ; they are one and the 

 same substance. If the constitution of the substance is that of a trihydroxy- 

 benzene or phenol, then the trimethyl ether should exhibit an absorption curve 

 differing but slightly in detail from that of the parent substance ; and, further- 

 more, the latter should exhibit a general resemblance to the curves of pyrogallol 

 and phenol. This was found actually to be the case in both particulars. 



Finally, with regard to tautomerism, it may be considered as decided that no 

 evidence has been obtained based upon either physical measurements or chemical 

 reactions of, first, the presence of a * wandering ' atom of hydrogen as a 

 characteristic of compounds which exhibit tautomerism ; secondly, that solutions 

 of tautomeric compounds do not contain equal quantities of the two substances, 

 or enolic and ketonic forms in equilibrium, and that if both are present one so 

 greatly preponderates over the other that no trace of any but the one compound 

 can be detected ; thirdly, it has been observed that some substances do change 

 spontaneously from one form to another, and that this change sets in very quickly 

 after the substance has been dissolved ; fourthly, that substances change from 

 one form to another under the influence of different reagents, as, for instance, 

 cotarnine, as Dobbie and Lauder (1903) have shown, in presence of methyl alcohol 

 or of caustic soda, and again in presence of potassium cyanide. In fact it appears 

 that under the influence of different reagents one or other of the two compounds 

 is the more stable, and the more stable substance is then formed. 



A reaction is recorded in the researches of Emil Fischer where it appears that 

 two tautomeric forms are produced simultaneously from oxycafeine. When the 

 silver salt of this substance is heated with methyl iodide it yields a mixture of 

 tetramethyl uric acid and methoxycafeine, the characteristic groupings in which 

 are -NH-CO- and -N = COH-, the hydrogens being methylated. This is a 

 singular reaction which has not yet been studied spectrographically. 







.n xr. 



\c— OCH, 



CH3— K/^'^C— n/ ' CH,— n/\c— N^ 



1 >co 



oc>. ^c— N< oa . 



N ^"» N 



IC— N'^'''' 



Oil 3 CH3 



I 



CI 



Tetramethyluric Acid. Methoxycafeine. 



Tlie Absorption Spectra 0/ Alkaloids. 



The interest attached to an examination of the absorption spectra of the alka- 

 loids is not alone the fact that a means of recognising, detecting, and estimating 

 3uch substances was devised, but still more that we may learn something of their 

 chemical constitution. Many of the poisonous alkaloids give no distinctive 

 chemical reactions, and in certain cases the means of recognising them are 



