164 Royal Society : — Mr. H. C. Sorby on Analysis of Animal 



1, B, aq 2 



Blue Lobelia speciosa 2|— 3 J. . .3f — 4§ 1 1 



!2 * * 



* tt 



Pink Matthiola annua 2|— 4J...4J— 5i...8 10. .11- 



Logwood (Hcematoxylum campechianum) 3f| — 5 J... 7— 8 — 



Brazil-wood (Casalpinia crista) 4| — 5f .. 7—8 — 



Such spectra are at once seen to differ most decidedly when compared 

 side by side ; and that the colouring-matters are entirely different is 

 proved by other facts. If the absorption-bands agree very closely, 

 we ought to compare other spectra before concluding that the sub- 

 stances are the same. 



22. Mixed Colours. 



Of course, if any impurity is present which absorbs that part of 

 the spectrum where the characteristic bands occur, it may be diffi- 

 cult, or even impossible, to determine the nature of the substance ; 

 but the rest of the spectrum may be obscured, and the general colour 

 entirely changed, without the least difficulty being thereby produced. 



Thus, for example, on adding a solution of Saffron (Crocus sativus) 

 to that of the blue Lobelia, the colour is changed from blue to a 

 curious olive, and the spectrum becomes — 



# 



Lobelia and Saffron 2 J— 3|...3f— 4§ §\..l- — 



Lobelia 2£— 3j...3j— 4§ 11... 



Difference ^i • • 7 



If we did not know it, we might thus infer that they were the same 

 substance, and only differed because one contained a yellow colour ; 

 and this conclusion would be borne out by adding to each citric acid 

 and sulphite of soda, which make the Lobelia colourless, and leave 

 the residual yellow colour, 6^ . . 7- — , in the case of the mixture. 

 The petals of very many flowers do really contain more or less of 

 such a yellow, which appears to be that developed to a much greater 

 extent in the stamens, &c. ; and though this often modifies the 

 general colour and the spectra, its presence may be recognized in a 

 similar manner. Different species of Bianthus, various kinds of Roses, 

 and Digitalis purpurea are good examples of one general colouring- 

 matter modified in this manner. Its normal character is 



* 

 1, A, aq am al am 1 (If -- 2|...4g 11 . .). 



In studying mixed colours, so much depends on their special charac- 

 ters, that it would be difficult to give any other general rules ; and 

 particular cases do not form part of the plan of the present paper. 



23. Spectra with no Bands. 



The principal difficulty to be contended with in this method of 



qualitative analysis, is in the case of the subgroups where no decided 



absorption-bands can be developed by any of the reagents. They 



can easily be divided into the groups A, B, and C ; but the difficulty 



