46 Dr. R. D. Thomson on Parieiin and on the 



to constitute their bases. If we then consider parietin as ana- 

 logous to a resin derived from an oil, we may arrange the 

 preceding analyses as follows : — 



Oil of parietin (hypothetic) C4Q Hjg 



Parietin C40 Hjg 0^4 



Oxide of parietin . . . C4QHigOi6 



Parietin as a test for Alkalies. 

 The effect of reagents upon parietin is striking. A very 

 minute portion of this substance will impart hs yellow colour 

 to a large quantity of alcohol, and this solution is sensibly 

 acted on by reagents. When to such a solution a drop or 

 two of nitric or muriatic or sulphuric acids are added, the 

 ■yellow colour imparted to it by the parietin becomes much 

 heightened, and even a very small proportion (much more 

 minute than that mentioned) will effect a sensible change. 

 When the solution is strong the addition of acid produces a 

 yellow precipitate. When caustic ammonia, in the smallest 

 quantity, is dropped into, or applied by means of a rod, to a 

 solution of parietin, the yellow colour immediately becomes a 

 rich red, inclining to purple. The same result is obtained 

 with caustic potash, caustic barytes, carbonate of soda, caustic 

 lime, &c. The extreme delicacy of parietin in detecting alka- 

 lies suggests its utility in the laboratory. An alcoholic solu- 

 tion may be kept for use, as the addition of a drop or two of 

 the solution to a considerable quantity of an alkaline liquor 

 will be immediately followed by a change to red ; or the pro- 

 cess may be reversed, by placing a few drops of the alcoholic 

 solution in a test-glass, and adding to it a drop or two of the 

 alkaline liquor. The alcoholic solution may be prepared 

 simply by digesting the lichen in cold alcohol of sp. gr. •840, 

 as 1 have found that a small portion of lichen will impart a 

 colour to a large quantity of alcohol, sufficiently intense to 

 serve as a very delicate test for alkalies. Observing the strong 

 colour which the alcoholic solution imparted to the filtering 

 paper which was used to purify the solution when first pre- 

 pared, I cut these into test-papers, and found that when pro- 

 perly impregnated with the solution, they were little, if at all, 

 inferior to turmeric paper in their delicate detection of am- 

 monia. Test-paper may be prepared extemporaneously from 

 the alcoholic solution, when it is wished to detect ammonia, 

 by dipping a piece of paper into the alcoholic solution and 

 then applying it in its wet state to the ammoniacal vapour. 

 The yellow colour is immediately transformed into a reddish- 

 purple tint, more distinct than the colour that becomes appa- 

 rent in turmeric paper of old preparation under similar cir- 



