a Yellow Colouring Matter. 196 



The formula, therefore, will be, according to this view, 



Co H4 O3 ; 



or we may, as in the preceding case, consider it as an oxide of 

 an oil, and the composition, when calculated, would be — 



Atoms. 



Carbon, ....... 40 65.21 



Hydrogen, 16 4.34 



Oxygen, 14 30.45 



and the formula, 



C40 H16 Ou ; 



exhibiting a stage in the oxidation of an oil similar to what 

 we meet with in the gradual production of resins from oils of 

 the turpentine type. In some respects the colouring matter 

 under discussion resembles a resin, and especially in its ap- 

 pearance, when precipitated from its solution in alkalies by an 

 acid. If we then consider parietin as a resin, deriving its origin 

 from an oil of the turpentine type, the preceding analyses may 

 be classed as follows : — 



Oil of Parietin, . , . . . . C40 His 



Parietin, . . . . . . . C40 Hie Ou 



Oxide of Parietin, C40 Hie Oie 



The effect of reagents upon parietin is striking. A very 

 minute portion of the substance will impart its 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. 



PARIETIN AS A TEST OF ALKALIES. 



The extreme delicacy of parietin in detecting alkalies, sug- 



