166 Intelligence and Miscellaneous Articles. 



25. Fading of Group C. 



Sometimes in examining colours of group C, advantage may be 

 taken of the different rate at which their acid solutions decompose 

 and fade when a considerable quantity of sulphite of soda has been 

 added to an acid solution. The two solutions should be made as 

 nearly equal as possible in all respects ; and then the rate of fading 

 may prove that they are very different, or may show that one is a 

 mixture. After fading, the addition of excess of ammonia may show 

 valuable facts. For example, the colour of the root of the red beet 

 (Beta vulgaris) is pink, but that of the leaves is red, the spectrum 

 differing from that of the root merely in having the blue end much 

 absorbed. On keeping acid solutions of both to which sulphite of 

 soda has been added, that of the root becomes colourless, and that 

 of the leaves yellow ; and thus, considering that acid solutions of 

 colours belonging to group C are very rarely pink, it is almost cer- 

 tain that the colour of the leaves is the same as that of the root, 

 but modified by the yellow colour so common in leaves. 



26. Conclusion. 



Such, then, is a general outline of the method which I have hitherto 

 found the most convenient in studying different colouring-matters, 

 and for determining to what individual species any particular colour 

 may belong. I need hardly say that it is just the sort of qualitative 

 analysis 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 satisfactory opinion, or at least one that 

 might meet all practical requirements ; and even under unfavourable 

 circumstances we might narrow the inquiry to a surprising extent ; 

 and if this can be said even now, surely further research cannot fail 

 to make it most useful in cases where ordinary chemical analysis 

 would be of little or no use. 



XX. Intelligence and Miscellaneous Articles. 



SOME OBSERVATIONS ON GLASS TEARS. BY E. REUSCH. 



THE glass tears I have seen almost all contain larger or smaller 

 hollow spaces. That these are essentially vacuous I ascertained 

 in the following manner : — The external surface of a tear, the hollow 

 space of which was pretty near the circumference, was removed 

 by means of emery paper (emery with shell-lac) ; then, by means 

 of a hard triangular steel borer, the outside coating was perforated 

 under oil ; at the moment of the perforation the hollow space became 

 filled with oil, with the exception of a minute bubble, which is as 

 likely to have arisen from air absorbed by the oil as from any gas 

 previously contained in the tear. 



The great force required to break off the tail seemed also remark- 

 able. If its least thickness exceeded 2 to 3 millims., and if more- 



