50 COLORATION IN POLISTES. 



sented by the formula CgH^N.^CeH^NH, ; it is benzene azo-benzene, in 

 which one hydrogen atom has been replaced by the group NH,. It is 

 very slowly soluble in hot water ; moderately so in alcohol and ether. 

 Its salts are decomposed by water and dye wool yellow. 



Chrysoidin, the second member of the series, is known as diamido- 

 azo-benzene and is represented by the formula C6H5N,,C6H3(NH,),. It 

 may be regarded as derived from the foregoing by the substitution of 

 another amido group for the H atom. It is a reddish orange amor- 

 phous powder very slowly soluble in water, yielding an orange solution 

 which turns red upon addition of HCl. It is reduced at 150° to aniline 

 and tri-amido-benzene, which is the third member of the series, or 

 phenylen brown. 



Phenylen brown is a brown amorphous powder represented by the 

 formula C6H^N2C6H3(,NH,)3. It is one of the constituents of the well- 

 known dye Bismarck brown. This may also be derived from benzene- 

 azo-benzene by nitration and reduction. 



A large number of tests were made upon these substances and par- 

 allel changes noted inthe pigments of Polistes. Thus phenylen brown, 

 when treated with yellow nitric acid or aqua regia, passes through 

 exactly the same color changes as does the brown pigmented chitin, 

 and the yellow solution finally obtained upon addition of NH^OH 

 yielded an orange-brown crystalline substance. The orange chrysoidin 

 passes through similar changes. Conversely, the aniline yellow upon 

 boiling with (NHJ2S dissolves and yields, upon cooling, a light red- 

 brown powder. Further treatment with the same reagent gives a 

 powder of a deeper tint. Chrysoidin may be darkened in the same 

 manner. In fact, all the pigments of Polistes which were examined 

 show great similarity in their chemical reactions with the compounds 

 of this series. 



A spectroscopic examination was made of the pigments in question. 

 If the pigmented integument of Polistes be boiled in concentrated 

 HjSO/or HCl, the greater part of it will pass into solution. If now 

 this solution be decanted off and diluted with water, it is said that the 

 chitin is precipitated, leaving the pigment in the solution. When the 

 solution is thus diluted, a very dark brown precipitate is thrown down, 

 and the liquid retained is of a yellowish-brown color. I do not pre- 

 sume to know what actually happens in this case, but since an equal 

 amount of transparent or very slightly pigmented chitin (it is difficult 

 to obtain absolutely transparent chitin), when boiled in the acid and 

 diluted, throws down a similar black residue and yields a solution 

 which is very much lighter in color, I think it safe to suppose that we 

 have in the dilute acid mentioned above, pigment in solution. 



