44j DB. LAUDEK LINDSAY ON CHEMICAL REACTION 



" 4- Certain lichens not coutaming tlie same colorific principles 

 which exist in the majority, at least, of the dye lichens that yield 



orcine, orcelne, and archil. 



** At present, however, I am quite unable to explain the caprices 



of this and other colour reactions in lichens.'* 



If the application of the bleaching-solution test requires such 

 nicety, and its results are so capricious, in a solution of colorific 

 principles in boiling alcohol, which is one of their most powerful sol- 

 vents, it is to be presumed that the application of the test must be 

 attended with greater difiiculty, and its results with less cer- 

 tainty, when a drop of the bleaching-solution is merely applied 

 to, or rubbed on, the lichen-thallus ! 



II. Liquor Sodce Chlorates. — A solution of chlorinated soda — of 

 what is known to chemists as hypochlorite of soda or sodium, con- 

 stituting the "Liqueur de Labarraque" of Prench, and "Labar- 

 raque's solution, or disinfecting fluid," of British pharmacy. Along 

 with hypochlorite of soda, the solution contains chloride of sodium 

 and bicarbonate of soda. As in the corresponding case of the lime 

 solution, the hypochlorous acid appears to be the principle on 

 which the reaction with the lichen- colorific principles depends* 

 This test was recommended to my notice by Dr. Stenhouse, who 

 wrote*, "I find the Tiypochlorite of soda even more useful than 

 hypochlorite of lime.'* I may here at once dismiss it from 

 further notice by stating that I was speedily induced to give up 

 its use by finding all its results negative. In cases where the 

 corresponding lime solution gave a red reaction, the soda solution 

 gave none ; while in no case was the reaction (if any) such as to 

 deserve record. 



III, Ziquor Potass<3e, otherwise known as solution of potash, 

 or of hydrate of potash. — From its rapid absorption of carbonic 

 acid, it should be used^esA; or if preserved, it ought to be kept 

 in closely-stoppered bottles. The latter, moreover, should be of 



on flint fflasa and oxidft of Ifiad. This 



action 



test has several advantages over the corresponding solution of 



ammonia, it gives on no vapours 



texture 



plant. Of all the reagents which have been applied by means of 

 tlie glass stirrer to the thallus or apothecia, potash solution is by 

 far tlic most easily applicable. Twenty years ago, and since that 

 period, I used, or have used, potash solution in the microscopical 



* Feb. 1867. 



