712 Mr. James J. Dobbie [April 4, 



to be applied, it is uunecessaiy to insist on the value of the confir- 

 matory evidence which can be obtained by the use of the spectro- 

 scope. 



The minutest quantities of alkaloids can be detected by this 

 means, the method rivalling the colour reactions for the alkaloids in 

 delicacy. Thus, with a quantity of strychnine not exceeding ^^^ of a 

 grain, a clearly defined spectrum of the alkaloid can be obtained. 

 The photograph of morphine already shown was obtained with ^^^ of 

 a grain of the alkaloid (Fig 5), and that of nicotine with y^ij. 



The spectroscope serves not only for the detection, but for the 

 estimation of alkaloids ; by comparing the spectrum obtained with 

 an unknown quantity of an alkaloid with a series of spectra obtained 

 by photographing known quantities of the same alkaloid, it is 

 possible to make quantitative determinations of a high degree of 

 accuracy. 



The use of the spectroscope in the detection and estimation of 

 alkaloids in cases of poisoning, possesses certain advantages of the 

 highest importance. One is that the material is not destroyed. The 

 solution which has been employed for the spectroscopic examination 

 can be used afterwards for the chemical examination. Another is 

 that a permanent record is obtained which is always available for 

 reference. 



So far my illustrations have been confined almost entirely to 

 colourless substances, because it is in connexion with the investigation 

 of such substances that most of the recent advances in the subject 

 have been made. 



As my last example, I shall take the case of a coloured substance 

 in which the method has been applied within the last year with 

 marked success. 



It will be remembered that considerable uneasiness was caused 

 when it became known some time ago that nitrogen peroxide is 

 sometimes employed to bleach flour. In the course of an enquiry 

 into the subject, it l^ecame necessary to determine the nature of the 

 colouring matter naturally present in flour. It was known that 

 many of the yellow and orange pigments, so widely distributed 

 throughout the vegetable kingdom, are either closely connected or 

 identical with carrotene, the orange colouring matter of carrots, 

 and it had been suggested that the colouring matter of unbleached 

 flour might be identical with, or belong to the same class of colouring 

 matters as this substance. It was impossible, however, to prove 

 this by the usual chemical methods, !)ecause the amount of colouring 

 matter in flour is so minute that its isolation in a pure state, and 

 in sufficient quantity for chemical analysis, was hardly practicable. 

 Carrotene, however, can be prepared in a pure state, and the happy 

 idea occurred to Dr. Monier Williams, of the Local Government 

 Board, who was conducting the investigation, to photograph its 

 absorption spectrum and compare it with that of the colouring matter 



