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XIX.— NOTE ON LAGKMOID AND LITMIN. By W. N. 

 HAETLEY, F.E.S. 



[Read, March 24, 1886.] 



Last year Mr. H. N. Draper introduced to the notice of the Physi- 

 cal Science Section of the Royal Dublin Society a new substance 

 called lackmoid, which appeared to have the same, or very similar, 

 properties to litmus. He kindly forwarded to me small specimens 

 of lackmoid and litmin. The following notes show, first, that these 

 are different substances ; secondly, that they may be of a similar 

 constitution ; but we have no decided evidence. 



Lackmoid. — O'Ol gram, was dissolved in 20 cubic centimetres of 

 alcohol, of 0'8 sp. gr., and mixed with 20 cubic centimetres of 

 water. The substance is soluble in strong alcohol, but insoluble 

 in water. Soluble in alcohol of 50 per cent, by volume. It re- 

 tained its colour with but slight alteration for several months, the 

 sole change being the acquirement of a blue tinge. This may be 

 due to the alkalinity of the glass of the bottle in which it has been 

 preserved. 



Litmin. — 0*01 gram, dissolved in 20 cubic centimetres of water 

 and 20 cubic centimetres of alcohol, of 0*8 sp. gr. added. This 

 substance is insoluble in strong alcohol, but soluble in alcohol of 

 50 per cent., and in water. The solution has become bleached by 

 keeping, notwithstanding that the bottle has been carefully stop- 

 pered and not exposed to bright light. 



The spectra photographed for each solution after dilution were 

 not remarkable ; the actinic absorption of the two substances being 

 much the same, even after the addition of acid. Lackmoid has 

 the more intense absorptive power in the visible spectrum; in 

 solution it is undoubtedly a better reagent than litmus. The 

 alcoholic solution may be added to water and used precisely as a 

 litmus infusion. 



