34 
ties in the mouth cavity; he proved, however, that gelatin and albu- 
min produced similar changes of color with alcoholic guaiacum. 
He therefore reached the conclusion that this change of color is with- 
out doubt due to the albumin of the saliva, since no change of color 
is observed if the mouth be deprived of saliva by previous washing 
with water. Similarly, according to Marc ( 285 ), it was pointed out by 
Goettling that a mixture of guaiacum resin, gum arabic, sugar, and 
water of peppermint becomes sensibly blue; that certain acids impart 
a bluish tint to guaiacum resin, and that this same change is brought 
about by sweet spirits of niter. 
In 1810 Planche ( 326 ) in a note on the sophistication of Jalap Resin 
and a means of recognizing the same, calls attention to the fact that 
guaiacum resin takes on an intense blue color when exposed for a few 
minutes to the vapors of nitric acid, and further that the fresh root of 
the horse-radish also has the power of turning the tincture of guaiacum 
resin blue. In order to show this, he says, it is only necessary to 
plunge a little piece of the fresh root into a glass containing the tinc- 
ture of guaiacum, when little by little the liquid acquires the color of 
indigo in sulfuric acid. In 1819 Taddey (sometimes spelled Taddei) 
( 416 ), having had occasion to knead together several species of gum 
resins and resins proper with different sorts of flour, observed that 
the mixture of wheat flour and guaiacum becomes blue, especially 
after water has been added to the mixture exposed to the air. At 
his suggestion Rudolphi ( 416 ) followed up the investigation of this 
subject. He found that a mixture of guaiacum resin v. ith pure starch 
does not develop a blue color when moistened and exposed to the air, 
nor is this blue color developed by other vegetable materials which 
do not contain zimome, the name proposed by Taddei for the constitu- 
ent of gluten insoluble in alcohol. He also observed that guaiacum 
. is not colored, or at least only slowly, by flours poor in gluten and 
that it is not colored by those flours in which the gluten has suffered 
any great alteration. He observed further that when gluten or 
pure zimome is mixed with guaiacum it develops a superb blue color 
instantly, but that such a mixture only develops this color in atmos- 
pheric air. Rudolphi therefore proposed to make use of guaiacum 
as a reagent for judging of the purity and quality of different kinds of 
wheat flour, and conversely, he recommended wheat flour as a reagent 
for testing the purity of guaiacum resin. 
In 1820 Planche ( 327 ) undertook to determine the nature of the 
substance which produces the blue coloration with guaiacum. He 
conceived the idea that air and light had nothing to do with the 
bluing of guaiacum for the reason that if this change of color is due 
solely to the action of air and light, why is it, he asks, that when 
guaiacum resin is mixed with certain substances it is colored blue or 
green, whereas when mixed with other substances its natural color is - \ 
