200 
DR. GLADSTONE ON CIRCUMSTANCES MODIFYING 
gave a most intense purple, with the citrate a wine-red solution, and with the acetate 
a precipitate. 
The th ree purple solutions were about equally deep in colour ; they were unaffected 
by the addition of any amount of iron salt, but were reddened by the addition of 
comenamic acid. The mixture containing the citrate was uninfluenced in the cha- 
racter of the tint, and almost so in the depth of it, by the addition of any amount of 
either the acid or the iron salt. It was quite evident from this, that comenamic acid 
has a great tendency to combine with sesquioxide of iron in place of water, and that 
it is capable of forming two distinct compounds. Indeed it was found that one equi- 
valent, or less, of comenamic acid uniformly gave with one equivalent of nitrate of 
iron a deep bluish-purple compound ; and that two equivalents, or more, gave a wine- 
red compound ; whilst any proportion intermediate between one and two equivalents 
gave an intermediate tint. 
Comenamate of potash and of ammonia gave similar results to comenamic acid 
itself; but the colour produced with the citrate at least was not so deep. The fol- 
lowing were the ratios : — 
1 eq. ferric citrate -|- 1 eq. comenamic acid gave ... 5 parts of red salt. 
1 eq. ferric citrate 4- 1 eq. comenamate of ammonia gave 4 parts of red salt. 
1 eq. ferric citrate -f- 1 eq. comenamate of potash gave . 2'9 parts of red salt. 
The addition of citrate of iron to a mixture of single equivalents of it and comena- 
raate of potash caused an increase of colour, but no amount turned the solution 
purple. 
Comenamic acid then is able to overcome the great affinity of citric acid for ferric 
oxide only so far as to produce the more acid salt. The purple comenamate was 
reddened instantly by citrate of potash, yet a large addition of that substance did not 
wholly destroy the colour. 
That comenamic acid has not so great an affinity for sesquioxide of iron as to be 
unaffected by the presence of nitric, hydrochloric or sulphuric acid, was easily demon- 
strated. The following experiment illustrates the action of such a substance. To a 
solution consisting of single equivalents of ferric chloride and comenamic acid, suc- 
cessive portions of hydrochloric acid were added. The original mixture was bluish- 
purple. 
Hydrochloric 
acid added. 
Colour of mixture. 
3 measures. 
6 measures. 
9 measures. 
15 measures. 
2\ measures. 
31 measures. 
55 measures. 
Bluish purple, but paler by an amount equiv. to 25 measures of water. 
Bluish purple, but paler by an amount equiv. to 40 measures of water. 
Bluish purple, but paler by an amount equiv. to 54 measures of water. 
Visibly redder, and paler by an amount equiv. to 80? measures of water. 
Red purple. 
Pink. 
Still perceptibly pink. 
The affinity then of comenamic acid for sesquioxide of iron, though very great, is 
