SPECTRUM ANALYSIS. 739 



k manner that the centre of the aperture exactly corre- 

 sponds to the centre of any of the cells used in the experi- 

 ments, which are all made to correspond in such a manner 

 that any of them, or this apparatus, may be placed on the 

 stage and be in the proper place without further adjust- 

 ment, which, of course, saves much time and trouble. 1 



In the preparation of vegetable colouring matters foi 

 the spectroscope, care must be taken to employ a small 

 quantity of spirits of wine ; filter the solution, and 

 evaporate it at once to dryness at a very gentle heat, 

 otherwise if we attempt to keep the colouring matters in 

 a fluid state they quickly decompose. It is necessary to 

 employ various reagents in developing characteristic spectra. 

 The most valuable reagent is sulphite of soda, which 

 admits of the division of colours into groups. Of the 

 mode of applying reagents, ample directions are given. 



Mr. Sorby's qualitative analysis is just the kind of thing 

 to employ in detecting adulterations in many substances met 

 with in commerce, as well as in inquiries where very small 

 quantities of material are at command. By this method 

 we might be able in a few minutes to form a very satisfac- 

 tory opinion, or at least one that might meet all practical 

 requirements, and narrow the inquiry to a surprising 

 extent ; if this can be said even now, surely further re- 

 search cannot fail to make it most useful in cases where 

 ordinary chemical analysis would be of little or no use - y 

 for in this way we may be able to detect the presence 

 of chlorophyll in some of the lower animal forms as 

 the amoeba, hydra, &c., or, on the other hand, the red 

 colouring matter of the blood, cruorine, in worms, molluscs^ 

 and insects. A number of colouring matters can be 

 obtained, by using ether, from sponges, polyzoa, and the 

 crustaceans; these, if examined in this way, may give 

 unexpected results. 



For further information on this interesting subject we 

 must refer the reader to Mr. Sorfcy's paper " On a Definite 

 Method of Qualitative Analysis of Vegetable and Animal 

 Colouring Matter by means of the Spectrum Microscope," 

 published in the Proc. Roy. Soc. No. 92, 1867. 



(1) See a paper by Dr. Gladstone, on the Spectra of Solutions of Salt* 

 Quart. Journ. Cliem. Soc. vol. xi. p. 86. 



