TiCHBORNE — Laboratory Notes. 83 



The steel points were placed in connexion tvith a four-inch inten- 

 sity coil and a small leyden jar was interposed in the circuit. The 

 battery used consisted of three Groves elements. In examining by this 

 method, ordinary glass vessels must be discarded, because even the 

 strongly marked fluorescence of turmeric is more or less masked by the 

 blue fluorescence of the glass. 



In a quartz cell (two plates of quartz in a frame of gutta percha), 

 these observations can be carried on with the greatest accuracy. Mr. 

 Draper's observations prove that, whilst the colouring matter of the 

 true seeds gave no fluorescence, the presence of so small a c^uantity of 

 turmeric as '005 per cent, could be readily detected. 



Before we are justified, however, in using this phenomenon as the 

 test for the presence of any substance, it is necessary to put it to a 

 crucial examination, such as that detailed above to find out how far 

 the particular substance under examination is capable of giving fluor- 

 escence. Eut it is not at all necessary that we should submit it to 

 the light of a spark in the practical application of the test. The 

 fluorescence of an ordinary white glass flask is not observable under 

 the ordinary diffused light of a laboratory, but the ordinary fluores- 

 cent substances (so called), are easily recognized under such condi- 

 tions. It is only necessary therefore to form a tincture of the sub- 

 stance to be examined. The observation of Mr. Horner'^'' wh.o finds 

 that fluorescence is wonderfully developed by castor oil, may be 

 made use of with great advantage. A drop of castor oil that has been 

 passed through adulterated mustard, upon a filter, appears green 

 when ch'opped upon a black plate in ordinary daylight. If 

 the mustard is pure, no coloration will be perceived. I have 

 met with some specimens of " Safl^ron," (the stigma and style of 

 Crocus sativus), which give a fluorescence. They were evidently 

 adulterated because the flowers of saffron give no fluorescence. This 

 saffi'on is a most expensive drug, and is therefore veiy liable to 

 adulteration. 



5. — On the Printing Inks of the Sixteenth and Seventeenth Centuries. 



The Printing Inks of the present century differ somewhat from 

 those of the sixteenth and seventeenth centuries, and as this difi'er- 

 ence may affect the preservation of valuable works of art, I have 

 thought it desirable to embody my observations upon this subject in a 

 short note. 



The present ink used in printing books and valuable works of art, 

 essentially consists of Carbon in a fine state of division, ground 

 up with a mixture of oils, soaps, and a substance called printer's 

 varnish. 



This last named substance may be viewed as the important vehicle 

 by which the Carbon, or pigments, is bound to the surface of the 



* Philosophical Magazine, September, 1874. 



