810 Wisconsin Academy of Sciences, Arts, and Letters. 
this solution it is precipitated unchanged by water. With po¬ 
tassium hydroxide solution it forms a deep yellow solution 
which upon exposure to the air goes to a deep red¬ 
dish yellow. It dyes wools mordanted with chromium a 
deep olive yellow color. 
The formula for ellagic acid given above was suggested by 
Graebe. 11 . Further work upon the constitution of ellagic acid 
by Goldschmidt, 12 also by Niernstein, 13 and by Herzig 14 has con¬ 
firmed Graebe’s formula. 
II. DERIVATIVES OF THE DIPHENYL METHANE SERIES OF HYDRO¬ 
CARBONS AND THEIR HOMOLOGUES. 
By far the greater number of pigments of known constitution 
falling under the degree of saturation C n H 2n __ 14 are derivatives 
of the diphenyl methane series and their homologues. Of these 
diphenyl methane derivatives there are representatives of the 
diphenyl methane, diphenyl ethane, and diphenyl propane ser¬ 
ies; but by far the greater number are referable to diphenyl 
methane. 
II. A. 1. Pigments referable to diphenyl methane. 
All the plant pigments of known constitution referable to 
diphenyl methane are tri, tetra, penta, or hexa hydroxy sub¬ 
stitution products of diphenyl methanone. In some instances 
it is true methoxy groups are substituted for hydroxy groups, 
while in others the elements of a molecule of water has been 
eliminated from the hydroxy groups, thus forming an oxide 
group. Indeed this latter condensation appears always to have 
taken place wherever the hydroxy groups are so located that by 
the elimination of the elements of a molecule of water there can 
be formed a cycle of six members. Thus some of the pigments 
of this group are dicyclic while others are tricyclic compounds, 
the third cycle being heterocyclic in as much as it contains an 
oxide oxygen. These pigments are all alike in that they form 
needle like crystals very similar in character, of a pale yellow 
color, (hence the name xanthone,) and of high melting point. 
11 Ber., 36, p. 212. 
ia Monatsh. f. Chem., 26, p. 1143. 
13 Ber., 41, p. 1649. 
14 Monatsh. f. Chem., 29, p. 363. 
