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different from picric acid. Slightly soluble in water. Deep sky
blue by day, red by night. Acids reddened the solution, alkalis
bringing back the blue. Nascent hydrogen destroyed the blue
color, but upon adding ammonia and exposing to the air the color
was reformed.

As but a small amount of substance was available the
analysis did not prove very successful.

In a succeeding paper (33) he attempted to show the rela-
tionship between phenylcyanine and indigo, but his method of
procedure would have thrown discredit even upon an embryonic
chemist. Since, he argues, phenolcyanine has twelve carbon
atoms, whereas indigo has sixteen, the problem is to introduce
four more carbon atoms into the former to convert it into the
latter. Whereupon he records with the greatest gravity how he
proceeded, first, to melt phenolcyanine at a moderate tempera-
ture with sodium acetate, then to dissolve the product in con-
centrated sulphuric acid, and finally throw down the sulpho acid
by adding an excess of water. A similar experiment was car-
ried out with phenolcyanine and nitro-naphthalene, using equal
equivalents of each ; for the former contained 12 carbon atoms,
and the latter twenty; and 12 -f- 20 -^ 2 16, which gives us
the number of carbon atoms in indigo ( !). "These sulpho-
acids," he writes, "mixed and saturated with ammonia or am-
monium carbonate, gave a small quantity of a purple black
product, insoluble in water and alcohol, but soluble in concen-
trated sulphuric acid, producing a dark, emerald-green solution.
This product is very similar, if not identical, to the black indigo
produced when the leaves are badly fermented."

And this is the last we hear of Phipson !

A notable contribution to the orcein question is that by
Liebermann (34). In the course of a study of the action of
ammonia upon orcinol, it occurred to him that possibly the com-
bined action of the ammonia and the oxygen of the air was
equivalent to nitrous acid. Accordingly he dissolved orcinol in
concentrated sulphuric acid, and added potassium nitrite, where-
upon a deep purple coloration was obtained. The addition of
water threw down a red flocculent precipitate, which was found


to be soluble in alkalis, giving a beautiful red solution. But the
substance was not identical with orcein.

Further work upon phenols assured Liebermann that phenols
in general responded to color tests with nitrous acid. Since his
day the Liebermann reagent (6 per cent, potassium nitrite in
cone, sulphuric acid) has been extensively used.

In a subsequent paper Liebermann (35) describes how he
repeated De Luynes's work and found that the action of am-
monia upon orcinol gave him a product part of which was read-
ily soluble in ammonia. The more insoluble part was dissolved
in sodium hydroxide. Both parts were now treated alike ; namely,
acid was added to each to precipitate the substance, which was
then washed, dissolved in alcohol, and the latter then evaporated.
Both substances were found to be amorphous, and outwardly
could not be differentiated. The purple color obtained with alkalis
showed a decided reddish tint with the first, and a more bluish
one with the second.

Wurster's paper on "The formation of color by means of
hydrogen peroxide" (36) is particularly worthy of close study.
He found that in the presence of hydrogen peroxide, ammonia
and phenol gave a blue coloration, which gradually changed to
green and then to yellow. The solution became quite decolorized
when an excessive amount of hydrogen peroxide was added.
The addition of acetone, alcohol, or oxalic acid considerably
hastened the reaction. Hydroxylamine was found to be still
more effective. This substance, together with phenol and hydro-
gen peroxide, formed nitroso-phenol, but neither a blue nor a
green color was evident. With the addition of ammonia the color
rapidly formed. As but a small quantity of hydroxylamine was
necessary, Wurster would explain this reaction by saying that
the hydroxylamine is oxidized to nitric oxide, which in the solu-
tion acts the part of an oxygen carrier.

To isolate the product Wurster gives these directions : To
an emulsion of phenol in water ammonia is added in such amount
a? to leave some of the phenol still undissolved. Some sodium
hydroxide and an equal volume of hydrogen peroxide are now
added, the whole diluted with ten times its volume of water, and
well shaken. The addition of a small crystal of a salt of hydrox-

2 7

ylamine causes a light blue color to appear within a few minutes.
This soon changes to deep blue, and in one or two days becomes
quite green. Without hydroxylamine the color develops quite
slowly, and the maximum intensity is not reached before twenty-
four hours, whereas with it a full development of color is notice-
able within a quarter of an hour.

By extracting the blue color with ether part goes into solu-
tion, giving a red coloration. A solution of amyl alcohol and
ether extracts more completely.

As the ether extract of the acid solution of the dye* is red,
and the Liebermann dye (nitrous acid on phenol) under similar
conditions is yellow, Wurster is inclined to believe that the two
are quite different; and this view receives support in that their
spectroscopic behavior is not the same.

Dealing next with the constitution of the blue product
Wurster states that the whole behavior of the compound points
to its identity with phenolquinoneimid, a substance first prepared
by Hirsch (37) by the action of quinonechlorimid on phenol,
though he could not isolate it.

Wurster prepared phenolquinoneimid by adding ammonia to
a watery solution of quinone in the presence of an excess of
phenol. The yellow quinone solution quickly becomes green on
the addition of ammonia, and blue by stirring in contact with air.
A still easier method is to start with /-amido phenol. By dis-
solving this in sodium hydroxide a red solution is obtained which
becomes yellow on contact with air. By the addition of phenol,
phenolquinoneimid is at once obtained.

By studying other phenols Wurster found that all phenols
that have the para position with respect to the hydroxyl group
unsubstituted form quinoneimids. Where the para position was
substituted the substances oxidized to a yellow product or were
not attacked at all.

The author concludes significantly by saying that since it
has been shown that both ammonia and phenol are decomposi-
tion products of proteins, the formation of color in plants bears
a certain relationship to the hydrogen peroxide that is present.

Zulkowski and Peters (38) carefully repeated Liebermann's
* Here the word is rather loosely employed.


work on the action of ammonia upon orcinol. By allowing a
mixture of 50 gms. orcin in 200 c.c. water and 200 c.c. ammonium
hyclroxid solution [strength not given] to stand for two months a
thick jelly was obtained, from which the following three colored
substances were isolated :

1) A red-colored product, orcein, obtained in microscopi-
cal crystals from a mixture of water and alcohol. With alcohol
it gives a carmine-red solution, and with ammonia, the fixed
alkalis, and the alkaline carbonates, a bluish-violet. Insoluble
in water. Yield, 50%.

2) A yellow crystalline substance, soluble in ether and al-
cohol, and less so in boiling water, in each case giving a yellow

3) An amorphous, litmus-like substance, with a greenish
metallic-luster. Insoluble in alcohol, soluble in alkalis to a dark
blue solution, which turns red on the addition of acids.

By the addition of hydrogen peroxide, the rapidity of the
process could be greatly increased. What required days before
could be accomplished in so many hours.

Under otherwise identical conditions resorcinol did not
yield an orcei'n-like substance ; but the latter could be obtained
by allowing orcinol (142 parts), resorcinol (110 parts), 22,%
ammonium hydroxide solution (7.7 p.), and 3% iI 2 O 2 (3 MM) p.)
to stand for several days. By recrystallizing the product from
alcohol a bronze lustrous substance was obtained, the red acetic
acid solution becoming blue upon the addition of ammonia or

Maseau (39) in a study of the comparative color reactions
of the phenols with ammonia and iodine in the presence of alco-
hol, describes the colors with ammonia as follows : Pyrocate-
chin, reddish-brown ; hydroquinone, yellow ; pyrogallol, black-
ish-brown ; orcin, red to violet. Phenol, resorcinol and naphthol
remained colorless.

It is quite apparent that the author did not take the time
element into consideration.


The brilliant Lallemand, in his exhaustive study of thymol,
refers to the action of ammonia upon it in no uncertain terms.

2 9

"Le thymol," he \vrites (10), "n'est pas altere par 1'ammoniaque
liquide ; mais il dissout une grande quantite de gaz ammoniac
qu'il abandonne lentement en se solidifant." This view became
the accepted one. We find Watt, for example, quoting it in his
dictionary (40). Just as in many another reaction a neglect of
the time element failed to give any visible result.

The first one to record any reaction is Lex (30). In de-
scribing some new color tests for phenol, the author records
that the addition of ammonia to phenol causes a blue color to
form under either one of the following conditions : a) Warm-
ing the solution with bleaching powder; b) warming with ba-
rium peroxide; or c) allowing to stand exposed to the air.
He adds, in a casual note, that he finds thymol to behave simi-

In a comparative study of the behavior of thymol and
phenol with various reagents, Hirschsohn (41) found that when
thymol (1:1000) was heated with bleaching powder and am-
monia the solution became cloudy, and after a time showed a
greenish tinge. In a concentration of 1 : 2000 and I : 4000 only
a cloudiness was obtained. The substitution of chlorine water
for bleaching powder produced a bluish-green coloration.

Wurster, in the article already quoted at some length (36)
showed that thymol, in the presence of hydrogen peroxide and
ammonia, forms a quinoneimid analogous to that obtained from
phenol. The acid properties of the resulting imid a red oil
insoluble in water were found to be so slight that dilute am-
monia had no tendency to salt formation. The blue sodium
salt could be decomposed with a large quantity of water, but
the potassium salt was more stable.

* The casual reference to thymol comes in the last three lines of the
article. The quotation in full is as follows: "Uebrigens zeigt das einzige
fernere Glied der Ph-enolreihe, welches ich zu priifen Gelegenheit hatte.
das thymol, insofern ein ganz analoges Verhalten." That this observa-
tion attracted no attention is seen by the fact that no mention of it wliat-
ever w to be found in She literature. It was only by the merest chance
that we came across this article, and then long after the experimental part
of this research had been begun. However, even had we stumbled across it
at the very beginning of this inquiry Lex's comment would merely have
given added impetus to our desire to inaugurate this investigation.


From the title of his essay "The role of hydrogen perox-
ide in the formation of color" we not only get the object of
this research, but also the author's opinion that the oxidizing
agent plays an indispensable part in the formation of the color.
This is emphasized more than once in the contents.

In a recent communication, Gies (42), in following up his
previous observations (1), shows that filter paper soaked in
the blue, alkaline, alcoholic solution (obtained from the blue
of an ammonium hydroxide-thymol mixture by extracting the
color with ether, evaporating the latter, dissolving in alcohol, and
rendering slightly alkaline), and then dried at room tempera-
ture, "assumes a bright red color as the alcohol disappears.
Treated with alcohol, such red filter paper, particularly if
slightly moist, becomes bright green." Interesting probabilities
suggested by these results, and the possible relationship of these
color phenomena to the pigments in the Monardas* and other
plants, will be investigated.


The first question that suggested itself was whether the
blue color was due to some impurity that was present in the
thymol? If so, the probabilities were that the same amounts
of different varieties of thymol would show marked differences
in intensity of color. Three varieties on the market, Merck's,
Eimer and Amend's, and Kahlbaum's, were procured, but no
differences could be detected (Table I).

In order to eliminate further doubt, it was decided to purify
the thymol. After several preliminary experiments, a conven-

* Wakeman : Bulletin of the Univ. of Wisconsin, No. 448 ; Science
series, 1911, IV, p. 25. Colored pigments in the corollas of Monardas
didyma, fistulosa, and punctata, are described. These are regarded as
probable oxidation products of the thymol and carvacrol. Hydrothymo-
quinone, thymoquinone, and dihydroxythymoquinone, have been isolated.
These are known to form colored compounds by combining with
monatomic phenols.

lent means of doing this was found to be to steam distil the
substance, and recrystallize the product from glacial acetic acid.*

As tests of purity, the melting points of the different sam-
ples were compared. However, even here one is beset with diffi-
culties, for in the literature melting points ranging anywhere
from 44 to 53 are to be found.f With a view to explaining
some of these differences, slight modifications in procedure were
adopted at different times (Table II). The last determination
(number 8), giving the melting point from 50-50.5 should be
taken as the most reliable.

From a glance at the table it will be seen that the melting
points of the different samples agree remarkably well. This
shows that the samples obtained from Merck, Eimer Amend,
and Kahlbaum, were equally pure, and that steam distillation

* In some of these steam distillations the thymol came over in the
form of a colorless oil; by merely transferring into another flask the oil
would solidify into a shining white mass. This solidification by mere
agitation is a marked characteristic, and has been noticed by many

If the condenser is too cold the thymol very readily solidifies in the
tube. A little alcohol or acetic acid will easily dissolve this.

As this phenol is exceedingly soluble in glacial acetic acid, and as
crystallization will not take place from a too dilute solution, quantities
of the steam distilled thymol were added to a small quantity of acetic
till an almost saturated solution was obtained (by the aid of gentle heat).
Then one or two c.c. more of the acid were added.

Thymol crystallizes from glacial acetic in large, colorless, hexa-
gonal plates, a mosaic of the crystals appearing on the surface.

In the course of these crystallizations an interesting means of study-
ing the development and formation of crystals was hit upon. This method
consisted in very slowly pouring an almost saturated solution of thymol
in glacial acetic acid into a large quantity of water. Soon small
droplets appear, and in these latter the nucleus of the crystal, in the s'hape
of a speck of white solid, springs into being. This enlarges and spreads
until the crystal is formed.

f Carnelly, in his "Melting and Boiling Point Tables" (1885), I, 224,
gives the following: Liquid (Febve) ; 44 (Lallemand, Sten'house,
Widman) ; 46 (Kekule and Fleischer); 48 (Arppe) ; 49.2 (Schiff) ;
51 (Andresen) ; 53 (Haines).

Fehling ("Handworterbuch der Chemie," 7, 969 (1905) ), supple-
ments this by giving Mentschutkin's (50) and Reinsert' s (49.7) figures.

3 2

and recrystallization did not tend to increase the purity. Above
all, the purified products reacted with ammonia in precisely the
same way, and to precisely the same extent as the non-purified


Comparison of intensity of color for different samp-es of



Thymol 0.5 gm. 0.5 gm. 0.5 gm.

Ammonia (10%)* 100 c.c. 100 c.c. IGOc.c.

Alcohol (95%)* 10 c.c. 10 c.c. 10 c.c.

A Merck product.

B Eimer & Amend product.

C Kahlbaum product.
Conclusion. Intensity about same in all.


Determination of the melting point of the ordinary and
purified thymol. [The numbers refer to C.]

Merck's Merck's steam

. p . , v , ,, steam distil, and

Merck Eimer & Amend Kahlbaum d ; st j lle j recryst.

from acetic

1. 48 47-48 47-48

2. 48 47-48 48

3. 49+ 48 49

4. 49+ (0.2-0.3) 49 49

5. 49 +(0.4-0.5) 49

6. 48 49

7. 48.5 48.5 49

8. 50-50.5 50-50.5 50.5 50.5 50.5
Notes. Roth's Melting Point Apparatus was used [see Ber.

d. D. Chem. Gesell. 19, 19TO (1886)]. Melting points were
taken only after complete fusion.

Note on the method of drying thymol: It was noticed that when
concentrated sulphuric acid was used as a drying agent in the desiccator
the acid gradually changed to a brownish-red color, and fine violet colored
deposits were repeatedly obtained. This result was always obtained in
the presence of thymol. Calcium chloride was therefore substituted.

* Unless otherwise stated the ammonia and alcohol used throughout
are respectively 10% and 95%. Alcohol was used on the supposition that
it favored the reaction by increasing the solubility of thymol. See page 44.



Having shown that the blue color is not due to an impurity
in the thymol, it became important now to establish definite
quantitative relationships in order to determine to what extent
the different reagents took part in the reaction. Since we were
here dealing with three factors, thymol, ammonia and alcohol,
the most logical method that suggested itself was to conduct
experiments on the basis of one variable and two constants.
Table III shows that the intensity of the color is proportional to
the amount of thymol present, but Tables IV and X show
that beyond certain limits this does not hold. In the same way
it was shown that the intensity of the color varied directly with
the amount of ammonia present (Table V), and subsequently,
that more concentrated solutions of ammonia inhibited the for-
mation of color.

The action of alcohol was most peculiar. It was at first
supposed, from the original experiments on elastin (1), that
alcohol would considerably accelerate the reaction. But this did
not prove to be the case (Table VI) ; and indeed, under certain
conditions, it acted as a retarding agent (Table VII).

Of course, this at once suggested the idea of dispensing
with the alcohol altogether, and most satisfactory results were
obtained (Table VIII).*

* One of the most interesting phenomena in these observations was
the behavior of thymol when added to the ammoniacal solution. As soon
as the powdered thymol touched the surface of the liquid it tended to form
globules. This was particularly marked when the quantities of thymol
added were comparatively large. When a globule had reached a certain
size it would sink to the bottom. Upon standing the globule would grad-
ually assume a reddish or violet tint, and a pear-shaped form. Two op-
posing forces now came into play, the upper liquid portion of the globule
which tended to force its way upward, and the lower, which restrained it.
The upper portion gradually increased in size, and after it had attained
a certain volume it broke away from the rest of the globule and came to
the surface, forming colored (usually violet) oily layers. A repetition
of the above phenomenon would now commence in the globule at the
bottom ; and, indeed, this would continue for several days, till finally the
entire globule had disintegrated. This might offer an interesting field for
physico-chemical study.


Under certain conditions water was found to take an inter-
esting part in the formation of color (Table XI).

With regard to the delicacy of the reaction, it was found
that within five days a distinct coloration was obtained in a
concentration of 1:25,000 (Table IX).


Effect of varying thymol, with ammonia and alcohol constant.

Thymol 0.1 gm. 0.2 gm. 0.3 gm. 0.4 gm. 0.5 gm.

Ammonia (10%) 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c.

Alcohol (95%) 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c.

Conclusion. Intensity of color varies directly with the
amount of thymol present.

Notes. Color noticeable one hour after commencing. Color
gradually changes from green to blue, the change taking four,
and perhaps more days.


What amount of thymol gives the maximum color?

Thymol ..0.02gm. 0.05 gm. 0.5 gm. 0.6 gm. 0.7 gm. 0.8 gm. 0.9 gm. 1.00 gm.
Ammonia. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c.
Alcohol... 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c.

Conclusion. Three gives maximum color.

Notes. One showed first trace of color in \ l / 2 hours. After
46 hours the color was still a very light green.

Intensity of colors in 4 and 5 about same as in 3, but
pinkish globules on top.

In 6 color somewhat less intense than 5 ; 7 and 8 showed
faintest trace of color after 1^ hours, but solution was very
cloudy. Pink globules on top. After 46 hours' standing the in-
tensity of the blue color showed but very slight sign of increase.


Effect of varying ammonia, with thymol and alcohol constant.
12 34 5678 9


0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm.


TABLE V Continued.


lOc.c. 20c.c. 30c.c. 40c.c. 50 c.c. 60 c.c. 70 c.c. SOc.c. 90c.c.

90 c.c. 80 c.c. 70 c.c. 60 c.c. SOc.c. 40 c.c. 30 c.c. 20 c.c. 10 c.c.

10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c. 10 c.c 10 c.c.

Conclusion. Intensity of color varies directly with the
amount of ammonia present.

Notes. After 26 hours, large crystals partly pinkish, partly
colorless separated out in 1.

After 41 hours' standing the solution in 2 changed to pink.

After 91 hours' 1 and 3 were slightly pink.

1 and 2 were repeated, and beyond getting smaller crystals
in 1, identical results were obtained.


Effect of varying alcohol, with thymol and ammonia constant.
123456789 10


0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gtn. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm .

100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c.

1 c.c. 2 c.c. 3 c.c. 4 c.c. 5 c.c. 6 c.c. 7 c.c. 8 c.c. 9 c.c. 10 c.c.

10 c.c. 9 c.c. 8 c.c. 7 c.c. 6 c.c. 5 c.c. 4 c.c. 3 c.c. 2 c.c. 1 c.c.
Conclusion. Intensity of color about the same in all.
Notes. No difference in intensity could be noticed even
after 22 hours.


Effect of variation of alcohol upon a comparatively large
quantity of thymol in the presence of a constant quantity of



Thymol 1 gm. 1 gm. 1 gm. 1 gm. 1 gm. 1 gm. 1 gm.

Ammonia (10%) 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c. 100 c.c.
Alcohol (95%). 10 c.c. 20 c.c. 30 c.c. 40 c.c. SOc.c. 60 c.c. 70 c.c.

Water 70 c.c. 60 c.c. SOc.c. 40 c.c. 30 c.c. 20 c.c. 10 c.c.

Conclusion. Intensity of color decreases with increase of


Notes. The difference in results between this experiment
and the one above is probably due to two causes: 1) Greater
quantity of thymol used; 2) greater differences in amount of

Purplish drops in 1, and to a less degree in 2 and 3; 4
hardly any; 5, 6, 7 none at all. This is due to the fact that the
more alcohol present, the more perfect the solution.

It has been noticed that whenever there is more thymol than
will dissolve, the excess tends to change to a pinkish color
sometimes appearing in the form of a pinkish precipitate, more
often as pinkish or purplish globules.


Effect of varying ammonia in the presence of a constant
quantity of thymol and in the absence of alcohol.

12 345 678 9


0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm. 0.5 gm.
Ammonia (10%)

10 c.c. 20c.c. 30 c.c. 40c.c. 50 c.c. 60 c.c. 70c.c. SOc.c. 90c.c.

90 c.c. SOc.c. 70 c.c. 60 c.c. SOc.c. 40 c.c. 30 c.c. 20 c.c. 10c.c.

Conclusion. Intensity of color varies directly with the
amount of ammonia present.

Notes. The color is obtained as well without alcohol as
with it.

1 began to show a faint trace of color only after 4 hrs.
(In the presence of 10 c.c. alcohol the same sample gave evi-
dence of color in l l / 2 hrs.)

1, 2, 3, 4, 5 contained crystalline precipitates (probably un-
changed thymol), the quantity decreasing from 1-5. 6, 7, 8, 9 did

2 4 5

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