solubilised and a dark coloured extract results, it is also possible to
remove the mechanically deposited phlobaphenes and oxidised tannins from
the finished leather, and, as a consequence, lighten the colour of the
leather. For practical purposes, bleaching with Neradol D is carried out
by brushing over the darkly coloured leather with a 2°-3° Bé. solution
of Neradol D, and then rinsing well with water, in order to remove the
solubilised tannin. A lighter colour may also be obtained by immersing
the leather in a liquor of the strength mentioned above for several
hours, and then rinsing with water, but by this procedure not only the
surface tannin is removed, but also tannin from the leather substance
itself; this method is therefore not suitable for heavy leathers which
are sold by weight.
The advantage of employing Neradol D as a bleach in this way is to be
found in the fact that, on the one hand, the bleaching sulphonic acid
attacks the leather to a much slighter extent than is the case with
inorganic acids usually employed for this purpose; on the other hand,
the method of brushing the sulphonic acid on the leather only introduces
small amounts of sulphonic acid in the leather, thus lessening the
harmful effects of acids upon leather. Furthermore, the common methods
of using alkalies as tannin-solubilising agents with the consequent
running off and waste of alkaline tan liquors are here substituted by a
method leaving liquors rich in tannin and Neradol, and which may be used
in the ordinary procedure of tannage.
Since Neradol D contains neutral sodium sulphate (about 3 per cent.),
and the latter, by precipitating colouring matters present in tan
liquors, may slightly bleach these, it was of interest to determine
whether the sodium sulphate plays any part in the bleaching effected by
Neradol. Mixtures of chestnut and quebracho extracts were prepared, to
which were added:--
(1) 5 per cent. Neradol D.
(2) 5 per cent. Neradol D. free from Na_2SO_4.
(3) ° 15 Per cent. sodium sulphate (corresponding to above
Neradol D).
These mixtures were allowed to act upon pelt alongside of comparison
tests using quebracho and chestnut extracts only, the strength of the
liquors in all cases being 1.5° Bé; the pelt was left in the solution
till tanned through. The following results were obtained:--
(1) Quebracho tanned leather was darker; no difference in
colour by chestnut extract.
(2) Similar to (I).
(3) Same colour as given by the original extracts.
This experiment demonstrates that absence of sodium sulphate in the
mixture is without influence on the colour of the resulting leather, and
that an addition of sodium sulphate to natural extracts does not affect
the colour imparted by them to pelt
5. Effect of Neradol D on Pelt
Being a sulphonic acid derivative, the chemical constitution of Neradol
is obviously considerably different from that of the natural tannins,
and the question has been asked: Will Neradol D, in its concentrated
form, attack the hide substance?[Footnote 1: _Collegium_, 1913, 521,
487.] Bearing in mind that concentrated extracts of vegetable tannins
in some circumstances effect a "dead" tannage (_cf_. case-hardening) and
hence reduce their practical value, and that for this reason it is
impossible to allow either concentrated extracts or concentrated Neradol
D to act upon pelt, the author still decided to carry out some
experiments in this direction. Concentrated Neradol D (33° Bé.) and
strong aqueous solutions of this material in strengths of--
30° 25° 20° 15° 10° 5° 3° 1° Bé.
were therefore allowed to remain in contact with pelt for a period of
ten days, when the pelts were taken out and washed in running water for
twenty-four hours, and then dried. The resultant leathers possessed the
following properties:--
33° Bé. solution: completely gelatinised.[Footnote 2]
30° " " " [Footnote 2]
25° " two-thirds gelatinised; surface tanned.
20° " one third gelatinised; surface "dead" tanned.
15° " pelt was glassy throughout.
10° " rather cracky leather, but well tanned.
5° " normal tannage.
3° " " "
1° " " "
[Footnote 2: Impossible to subject the pieces to a proper washing out.]
The interiors of the leathers obtained from the 25° and 20°
Bé. solutions were completely gelatinised; this may be accounted for by
assuming that the surface was "dead" tanned, and that hence the free
dissociated sulphonic acid diffused into the leather, towards which it
exhibited hydrolysing rather than a tannoid effect with the consequent
result described above. Above 10° Bé. the effect is more that of an acid
with concentrations below 10° Bé.--the only ones of technical
importance--however, no ill-effects may be observed.
For tanning purposes, Neradol D solutions of 2° Bé. are quite
satisfactory, and it has been found [Footnote 1: _Technikum_, 1913, 80,
324.] that solutions of this strength do not dissolve out any protein of
the hide. [Footnote 2: The translator cannot agree with the author on
this point. He has, for instance, found that solutions of analytical
strength dissolve considerable amounts of hide substance, and his
practical experience confirms results arrived at in the laboratory.]
A purely Neradol D tanned leather may be produced by immersing a bated
pelt, free from lime, in a 2° Bé. Neradol D liquor for about four days;
the resultant leather being nearly white and otherwise very similar to a
leather tanned with vegetable tanning materials.
The main application of Neradol D is in admixture with vegetable tanning
materials; especially in the early stages of tannage is this substance
of value, since by its use not only a light coloured leather surface is
obtained, but its presence prevents a subsequent dead tannage when
strong vegetable tan liquors are applied, and it also imparts strength
to the grain layer. It is thus possible to shorten the time consumed by
the tanning process by employing Neradol D in the manner described.
A further explanation as to why the tanning process is considerably
hastened by using Neradol D, either alone or in conjunction with natural
tannins, is afforded by the fact that though Neradol D quickly
penetrates the grain, it is but "loosely" fixed by the latter, _i.e._,
it is not deposited to such an extent that it would prevent penetration
of the vegetable tannins. In the case of a mixture of Neradol D and
vegetable tannins, the former quickly diffuses into the pelt and fixes
the fibres, thus facilitating penetration of the vegetable tannins.
This assumption is justified in view of the speed with which Neradol D
completely penetrates and tans the pelt, since Neradol D containing
acids and salts exhibits effects similar to those of a pickle.
6. Reactions of Neradol D with Iron and Alkalies
A special characteristic of Neradol D tannage is the sensitiveness of
the latter to the action of iron and alkalies. The active principle of
Neradol D being free dicresylmethanedisul-phonic acid, which is easily
neutralised by lime, ammonia, and amino-acids and hence rendered
inactive for tanning purposes, it is essential that the pelt prior to
tannage with Neradol D should be completely delimed, bated, and freed
from all constituents possessing alkaline reaction. It is, however,
possible to regenerate Neradol D liquors contaminated with alkali or
partly neutralised by the addition of small quantities of organic
(formic, acetic, lactic, and butyric) or inorganic (hydrochloric or
sulphuric) acids,_i.e._, the dicresyl-methanedisulphonic acid is again
partly liberated, and this procedure is always preferred where the
tanning process does not allow of a complete deliming of the pelt prior
to introducing the latter into a Neradol D liquor. If, on the other
hand, such liquors are kept properly, and the addition of acid referred
to kept up, they will remain active for weeks and need only
strengthening up with the requisite quantity of Neradol prior to
introducing fresh pack.
The sensitiveness to alkalies of Neradol D is considerably greater than
in the case of natural tannins, and it appears that a vegetable tan
liquor neutralised with lime will not even surface-tan when acting upon
pelt and will neither impart a dark colour to the leather nor remove
from it any appreciable amount of protein. Similarly, a Neradol D liquor
neutralised with lime exerts no tanning action, but in contradistinction
to the vegetable tan liquor similarly treated, will impart a blue or
blackish-blue colour to the pelt, from which it removes larger
quantities of protein. The author examined two such liquors relating to
their contents of tanning matters and protein and obtained the following
results:--
Reaction. Bark. Tans. Non-Tans Insol. Proteins
Per Per Per Per
Cent. Cent. Cent. Cent.
Vegetable Slightly 12° 0 2.93 0.35 0.01
tan alkaline
liquor
Neradol " " 10° 0 4.43 0.17 0.17
These figures do not only show the higher protein contents of the
Neradol D liquor, but do also show higher contents in soluble
non-tannins, which consist mainly of lime (2.12 per cent.) and sodium
salts (1.8 per cent.), thus establishing the fact of the sensitiveness
of Neradol D to alkalies in addition to its lime-solubilising effects.
The sensitiveness towards alkalies is also noticeable on a large scale
where the tanpits have been built of cement; though the pelt may be
quite free from lime, the Neradol D is quickly neutralised by the
cement, with results similar to those enumerated above.
The blue coloured soluble compound of Neradol D and iron salts, to which
frequent reference has been made, is very important from a practical
standpoint. Whereas the catechol tannins (_i.e._, fir, gambir, hemlock,
cutch, mangrove, and quebracho) are coloured black, those of the
pyrogallol class (_i.e._, algarobilla, dividivi, valonea, gallotannic
acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins
(_i.e._, canaigre, oak, and mimosa bark) bluish-purple by iron alum,
Neradol D is coloured a pure blue. How sensitive this reaction is, the
following comparative analyses illustrate: to each litre of tan liquor
containing 4 gm. tanning matter prepared from (_a_) quebracho extract
and (_b_) Neradol D, 10 c.c. of a 10 per cent. iron alum solution were
added, the solutions heated to 100° C., cooled and filtered, and the
colour of the filtrates and the weight of the precipitates determined:--
(_a_) Quebracho solution: light reddish-brown filtrate, 3.22 gm.
precipitate.
(_b_) Neradol solution: deep blue filtrate, 0.02 gm. precipitate.
Hence, on adding a soluble iron salt to a solution of a natural tannin,
most of the tanning matter is precipitated; the colour of the filtrate,
however, is much the same as that of the original solution. A Neradol D
liquor similarly treated gives no precipitate, but is coloured blue
throughout. The filtrates from the above solutions were allowed to act
upon pelt, and the following observations were made:--
(_a_) The light reddish-brown filtrate from the quebracho liquor
exhibited no well-defined tanning effect on pelt, to which it imparted a
light brown colour.
(_b_) On the other hand, the deep blue filtrate from the Neradol D
liquor exhibited well-defined tanning effects, and imparted a deep blue
colour to the pelt.
For practical purposes, the sensitiveness of Neradol D to iron is not
only remarkable because any contact with iron particles will colour the
liquor (and hence the pelt) blue, but also because the slight amount of
iron always present in cement renders the use of cement pits prohibitive
where Neradol D liquors are used.
This intense blue coloration might have made possible a colorimetric
estimation of Neradol D. The author has investigated this possibility,
using different concentrations of Neradol D liquors to which a solution
of iron ammonium alum was added, and found that when, at certain
concentrations, the maximum blue colour had been obtained, it was still
possible to increase the quantity of Neradol without the intensity of
the colour being affected. Addition of a little alkali tends at first to
darken the blue colour, more alkali changes the blue colour to brown and
yellow, successive additions of a weak organic acid (_e.g._, acetic
acid) rapidly lighten the blue colour. Since industrially used Neradol
D liquors always contain varying quantities of acid and may be neutral
or even slightly alkaline, it must be considered impossible to make any
use of such a colorimetric estimation for practical purposes.
7. Reagents Suitable for Demonstrating the Various Stages of Neradol D
Tannage
The extent to which tannage with Neradol D proceeds on the surface and
within the pelt may be judged from the feel of the skin, but such a
method is totally unsuited to any but a practical tanner. A suitable and
reliable reagent is indigotine (B.A.S.F.), which clearly distinguishes
tanned and untanned layers of the pelt. If, for instance, a 1-2 per
cent, solution of indigotine is brought into contact with a fresh cut on
a pelt, and the latter subsequently washed with warm water, the
indigotine is only retained by the untanned parts; a leather tanned with
Neradol D is therefore only coloured by indigotine to the extent to
which it has combined with the Neradol. [Footnote: According to Seel
and Sander (_Zeits. f. ang. Chem._, 1916, 333), basic dyestuffs are also
very suitable for demonstrating tanned parts of the pelt.]
Another reagent is constituted by iron ammonium sulphate; the extent of
the penetration of Neradol D, which gives an intense blue coloration
with iron salts, into the leather may be determined by washing the pelt
treated with Neradol D, making a cut, again washing and treating the cut
with a few drops of a weak solution of iron ammonium sulphate. Those
parts of the pelt which have been converted into leather then appear
deep blue; on the other hand, those which have been in contact with
Neradol D, but have not yet been converted into leather, are light
blue. Those parts which have not yet been in contact with Neradol D
appear pure white; the results of this reaction are therefore opposite
to those obtained by the use of indigotine.
8. Combination Tannages with Neradol D
Whereas mixtures of Neradol D and vegetable tannins impart properties to
the leather consistent with the proportions in which these materials are
present, it is not possible to combine Neradol D with mineral tanning
agents or fats (_e.g._, fish oils, etc.) in such a way that a leather
characterised by the properties of either material is
obtained. Experiments were carried out using (1) chrome salts plus
Neradol D; (2) aluminium salts plus Neradol D; and (3) oils plus Neradol
D, and the following conclusions were arrived at:--
1. CHROME-NERADOL D liquors, containing comparatively larger amounts of
Neradol D, act too rapidly on the pelt and draw the grain; smaller
amounts of Neradol D seem without influence on the finished leather,
which possesses pronounced characteristics of chrome leather. Another
disagreeable factor is the following: the chrome salts must possess a
certain degree of basicity in order to produce good leather; the Neradol
D must, on the other hand, possess a certain acidity to produce the
optimum results, and it is hence impossible to balance practically the
basicity of the chrome salts and the acidity of the Neradol in order to
justify the presence of both. If one of the two is used separately
before the other, a leather always results possessing the
characteristics of the material first employed, provided the time of
action has been sufficiently extended. If insufficient time has been
allowed, the characteristics imparted by the main tanning agent are not
altered.
2. ALUMINIUM SALTS AND NERADOL require practically the same basicity and
acidity respectively, and when combined always yield a leather
possessing mainly the properties of one of the components. In addition
to this fact, leathers tanned with aluminium salts possess great
softness and stretch, those tanned with Neradol D greater firmness and
less stretch, and these opposing qualities completely compensate one
another and render _nil_ the value of such mixtures.
In addition to this, the presence of aluminium salts produces no better
fixation on the leather fibre of basic coal-tar dyes, so that in this
respect also a combination of aluminium salts and Neradol D is of no
value.
3. FAT NERADOL D TANNAGE: Just as aluminium salts impart special
characteristics to leather, this property is exhibited by fatty matters,
especially so as regards stretchiness and softness. Both of the latter
are not apparent to the same extent in an oil tannage into which Neradol
D and oil enter as constituents. It is, however, not excluded that, in
view of the fact that the combination of oils and Neradol D appear to
produce the most promising results of the three from a technical point
of view, such combination would yield products possessing less stretch
and greater softness which, by occupying an intermediary position, might
possess certain advantages and be useful for certain technical purposes.
9. Analysis of Leather Containing Neradol D
Chemical examination of leathers tanned with Neradol D or with mixtures
of natural tannins and Neradol D often involve a determination of the
materials employed in tannage. In most leathers exclusively tanned with
vegetable tanning materials, it is usually possible to determine at
least the nature of the main tanning agent, whereas the attempts at
determining those tannins which are only present in minor quantities
rarely succeed. Since Neradol D usually is employed in comparatively
small quantities, it has been imperative to find a method which also
permits of the detection of smaller quantities of Neradol D. Provided
the presence of not less than 5 per cent. (on the weight of the leather)
of Neradol D, the following method yields reliable results:--20-30
gm. of the leather are ground or sliced as finely as possible and the
powder (or the slices) treated in the cold with a sufficient volume of
dilute ammonia solution (5 c.c. ammonia plus 95 c.c. of water) for
eight to twelve hours. The object of this is to dissolve the tannins,
but no protein should go into solution. The solution is filtered and
the filtrate evaporated on the water bath till it occupies a volume of
about 30 c.c. A few c.c. of aniline hydrochloride are now cautiously
added, when it should be carefully noted if a precipitate is thrown down
which might be either completely or only partly soluble in excess of
aniline hydrochloride. A precipitate is always thrown down when Neradol
D or wood pulp is present; only the Neradol D precipitate is soluble in
excess of aniline hydrochloride. Partial solubility of the precipitate
therefore indicates the presence of both wood pulp and Neradol D.
The quantitative determination of sulphuric acid--the detection and
estimation of which in leather is important--is considerably influenced
by the presence of Neradol D. Practically all methods in vogue dealing
with its determination were based on the estimation of the sulphur
introduced into leather by sulphuric acid. The presence of Neradol D,
the main constituent of which is dicresylmethanedisulphonic acid,
renders it impossible by such methods to determine whether the combined
sulphur owes its origin to sulphuric or sulphonic acid. It remains yet
to be determined whether the sulphonic acid influences the leather
substance to the extent that sulphuric acid does; it must, however, be
borne in mind that Neradol D in addition to free sulphonic acid also
contains sulphonates and sulphates, which may enter into the leather and
thus increase the sulphur contents of the latter. A method must hence be
devised which estimates the free acid only and provides the means of
distinguishing this from all other acids of organic and inorganic
acids. Paessler, [Footnote: _Collegium_, 1914, 527, 126; 531, 509; 532,
567.] by extracting the leather and dialysing the filtrate, has
effected a separation of the acids and the tanning and colouring matters
and quantitatively estimated the sulphuric acid in the dialysate.
Immerheiser [Footnote 1:_Collegium_, 1918, 582, 293.] devised a method,
based upon the property of sulphuric acid of combining with ether, for
the purpose of determining free sulphuric acid in leathers:--10 gm. of
the leather, cut into small pieces, are extracted three times with 200
c.c. distilled water at room temperature, the time of each extraction
being ten to twelve hours, and the combined extracts evaporated to
dryness on the water bath, 5 gm. of quart sand being added. The dry
residue is now powdered, introduced into an Erlenmeyer flask provided
with a glass stopper, and 200 c.c. of anhydrous ether [Footnote 2: To be
tested for water by shaking with anhydrous copper sulphate.] added.
After about two hours, during which the flask is occasionally shaken,
the ether is poured through a filter, the residue washed with a little
ether, and the operation repeated twice with each 40 c.c. anhydrous
ether, using the same filter. To the combined ether extracts (about 200
c.c.) HCl and [Greek: b]aCl_2 are added, the ether distilled off and the
residue evaporated on the water bath, in order to decompose the
ether-sulphuric acid compound. 50 c.c, of hot water acidified with HCl
are now added, the precipitate allowed to settle, filtered, washed,
dried, and weighed. The sulphuric acid thus estimated was present in the
leather as _free sulphuric acid_. That present as sulphates soluble in
water is estimated in the residue on the filter: the residue is
extracted with hot water, the sand filtered off, the filtrate acidified
with HCl, boiled for one quarter hour and filtered if necessary. The
clear filtrate, which may be coloured, is brought to boil and
[Greek: b]aCl_2 is added. The barium sulphate indicates the sulphuric
acid present in the leather as water-soluble sulphates.
Whether the latter be sulphates or bisulphates may be indicated by the
aqueous extract of the above residue, since neutral reaction would
indicate the absence of bisulphates, acid reaction their presence in
addition to possible normal sulphates; the quantitative estimation of
the metals would decide this point definitely.
10. Properties of Leathers Tanned with Neradol D
Whereas the colour of leathers tanned with Neradol D only is nearly a
pure white, those tanned with mixtures of Neradol D and vegetable
tanning materials are more or less light coloured according to the
quantity of Neradol D present, as has been explained when discussing the
phlobaphene-solubilising action of Neradol D. In any case, all leathers
tanned with Neradol D possess fibre of remarkable length, which explains
their increased tensile strength and elasticity. The tensile strength
of a leather tanned with a mixture of Neradol D and vegetable tannins
was 3.7 per cent, as compared to 3 per cent when no Neradol was used;
the extension was 56 per cent, when tanning with Neradol D as against 36
per cent, without the latter.
The sensitiveness to light of leathers tanned with Neradol D may be
mentioned. Exposed to direct sunlight, the surface of the leather
assumes a yellowish colour after two days' exposure, and assumes a pure
yellow colour after a further three days. A further fifteen days'
exposure only darkens the leather slightly, the final colour being very
little different from the one obtaining after five days' exposure.
In passing, it may be remarked that this yellow colour is observed on
the surface only, the grain otherwise possessing that pure white colour
characteristic of Neradol D tanned leather. Further, it may be noted
that leathers tanned--with Neradol D fix basic coal-tar dyes
excellently, whereas acid and substantive dyestuffs are fixed with other
than their natural shades.
The author has analysed a leather exclusively tanned with Neradol D, and
has obtained the following results:--[Footnote: _Collegium_, 1913, 521,
478.]
Moisture - - - - - 15.53 per cent.
Ash - - - - - - 0.93 per cent.
Fats- - - - - - 1.26 per cent.
Extraneous matters - - - 0.00 per cent.
Leather Substance |Tanning matters- 36.92 per cent.
Leather Substance |Hide substance - 45.36 per cent.
---------------
100.00 per cent.
[Footnote: Sp. gr., 0.642.]
From these figures, those of "degree of tannage" and "yield"
(pelt-->leather) are calculated as 81.4 and 220 respectively.
These figures correspond closely to those obtained by the analysis of
leathers tanned with vegetable tanning materials, and this proves the
similarity between the Neradol D tannage and a vegetable tannage in
their chemical aspects.
11. Neradol D Free From Sulphuric Acid
In order to prepare phenol and cresulphonic acids, such quantities of
technical sulphuric acid are used as do not allow of the assumption of
complete utilisation of the sulphuric acid; hence it was of theoretical
interest to remove eventual traces of free sulphuric acid from the
product. For this purpose, the author diluted crude Neradol to 20°
Bé. and gradually added small quantities of milk of lime; the
precipitates were freed from the liquid by suction and washing, and a
Neradol free from sulphuric acid resulted, which was then brought to the
acidity of Neradol D with the calculated amount of alkali. From the
calcium sulphate precipitate, the amount of sulphuric acid originally
present was calculated, and was found to be only 4 per cent.
The acid-free sample of Neradol was tested with regard to its
suitability as a tanning agent; leather tanned with this sample differed
from one tanned with an untreated sample (Neradol D) by being harder and
possessing a pronouncedly greyish colour. This difference, however, may
not be due to the absence of sulphuric acid but to the presence of the
slightly soluble calcium sulphate in the sample treated with milk of
lime. To prove this point, another way of preparing Neradol D free from
sulphuric acid was looked out for. Sodium acetate was added to a
solution of crude Neradol until the latter was no longer acid to
congo-red; at this point no free sulphuric acid can be present in the
solution. The product, partly neutralised till the acidity of Neradol D
was reached (part of the acidity then being due to liberated acetic
acid), yielded a leather which neither in colour nor in feel differed
from the usual Neradol D tanned leather. This proves that the grey
colour and the hardness of the leather described in the former
experiment is due to the presence of calcium sulphate.
If the crude Neradol treated with sodium acetate is not partly
neutralised, the analysis gives the following figures:--
Tanning matters 67.3 per cent.
Soluble non-tannins 8.6 "
Insolubles 0.0 "
Water 24.1 "
---------
100.0 per cent.
Acidity: 1 gm. = 46 c.c. N/10 NaOH.
Compared to the analysis of crude Neradol containing sulphuric acid, the
figures show that, on the one hand, the presence of the comparatively
small quantity of sodium acetate but slightly influences the contents of
non-tannins and water, but, on the other hand, reduces the contents of
tannins and also the acidity. The tanning intensity of this product,
however, is considerably increased, and using a 1° Bé. solution a
leather is obtained in a very short time very similar to that yielded by
ordinary Neradol D, but considerably harder; the latter property is due
to higher acidity and almost complete absence of salts in the product
treated with sodium acetate.
The author finally attempted to partly neutralise crude Neradol with
various hydroxides and carried out tanning tests with samples containing
the different metals. Hardly any difference in the finished leathers
could be observed as regards colour or quality; the tannage could by no
means be described as that of a combination of Neradol D and the
respective metals.
12. Neutral Neradol
Crude Neradol, completely neutralised with caustic soda, yields a
product of the following composition:--
Tanning matters 19.8 per cent.
Soluble non-tannins 37.9 "
Insolubles 0.0 "
Water 42.3 "
------------
100.0 per cent.
The qualitative reactions of this product differ from those of
non-neutralised Neradol to the extent that gelatine is not precipitated
and iron salts are not coloured blue, but dirty brown, by the aqueous
solution of this product.
The completely neutralised product, diluted to various concentrations
(of 1°, 2°, 3°, and 5° Bé.) and tested as to tanning properties,
revealed the surprising fact that the pelts were not even surface
tanned, and were coloured evenly blue throughout by indigotine.
It might have been anticipated that sodium dicresylmethanedisulphonate
would be as devoid of tanning powers as is a neutralised vegetable
tannin, but it is difficult to explain the fact of the sodium salt being
adsorbed by hide powder as "tanning matters" in the Official Method of
Analysis. Brought to a logical conclusion, the figure 19.8 per cent,
should be deducted from 32.5 per cent, obtained in the analysis of a
_partly_ neutralised Neradol D, which comparatively large quantities of
the sodium sulphonate also adsorbed by hide powder, leaving the "tanning
matters" of Neradol D at 13.5 per cent.
This diminished figure, however, does in no way reduce the value as a
tanning agent of Neradol D; it merely shows how inadequate is the hide
powder method of analysis when applied to substances of the composition
of Neradol D. This is further confirmed by the Loewenthal permanganate
method, which yields the following figures:--
Tanning matters 7.2 per cent.
Soluble non-tannins 59.1 [Footnote: Collegium, 1913, 521,487.]
If, on the other hand, completely neutralised Neradol is acidified with
an organic acid, such as acetic acid, till the acidity, (1 gm.= 10
c.c. N/10 NaOH) is reached, the resulting product is in all respects
similar to Neradol D and yields a corresponding leather.
It is permissible to assume that the irregularity exhibited by Neradol D
as regards the analytical estimation of its tannin contents is connected
with the low molecular weight of the tanning principle. Whereas all
tannins so far isolated from the natural tanning materials possess
rather high molecular weights, that of Neradol D deviates considerably
from this rule, as is shown by the following table:--
Neradol D tannin Cl_5H_16S_2O_8 358
Mangrove " C_24H_40O_2l 670
Oak bark " C_28H_28O_23 840
Myrabolam " C_54H_48O_35 1256
Dividivi " C_54H_46O_35 1270
Malletto " (C_4lH_50O_20)_2 1724
This low molecular weight may mainly account for the figures obtained by
the incorrect oxymetric estimation with permanganate; the apparent
tannoid property of the tannoid-inactive neutral salt of
dicresylmethanedisulphonic acid may be explained by assuming that though
it is, probably, in the colloidal state, and as such adsorbed by hide
powder, it is still devoid of astringent properties.
G. Different Methods of Condensation as Applied to Phenolsulphonic Acid
In addition to formaldehyde, many other substances may, theoretically,
induce condensation of phenolsulphonic acid; condensation takes place
either with the elimination of water or, in addition to this, with the
introduction of methane group.
So far, the following condensing agents have been investigated:--
(1) Heating _in vacuo_.
(2) Sulphur chloride.
(3) Phosphorus compounds.
(4) Aldehydes.
(5) Glycerol.
1. Condensation Induced by Heat
If phenolsulphonic acid is heated _in vacuo_ at 130° C. for twenty
hours, condensation takes place [Footnote: Austr. Pat., 64,479.]
without the addition of any condensing agent, and an anhydride of the
^ __O__ ^
| | | |
| | | |
v v
HSO_3 HSO_3
composition is formed. This product is a viscous liquid, possessing a
very corrosive action. Added to a solution of gelatine, a light, fine
flocculent precipitate is thrown down. Analysed by the shake method of
analysis, the tannin content of the product equals about 46 per
cent. Its strongly acidic and hence swelling character does not express
qualities consistent with the conception of suitability for tanning
purposes: a sample of the product was therefore partly neutralised to
the acidity of Neradol D, when the shake method of analysis yielded the
following figures:--
Tanning matters 21.5 per cent.
Soluble non-tannins 48.3 "
Water 30.2 "
--------------
100.0 per cent.
This partly neutralised sulphonic acid represents a white, pasty mass,
which is not particularly easily soluble in water, yielding a solution
of milky appearance. Treated with the usual tannin reagents, it exhibits
the following characteristics:--
Gelatine Light Flocculent precipitate.
Bromine water Compete fixation.
Ferric chloride Cherry-red coloration.
Lead acetate Very slight Percipitate, insoluble HNO_3.
Aniline hydrochlonde Slight percipitate.
Solutions of this product in concentrations from 1°-8° Bé. exerted no
tanning action whatever, whereas more concentrated solutions (15° Bé.)
converted pelt in eight days into a leather very similar to a Neradol D
leather in colour and feel, but considerably harder.
In order to determine its phlobaphene-solubilising effects, samplesof
the product were mixed with concentrated quebracho extract in the
proportions 5,10, 20, and 30 per cent. on the weight of extract, and the
following observations made:--5 and 10 per cent. were without effect,
20 and 30 per cent. showed some solubilising tendency, but on diluting
the mixture with water the quebracho was completely thrown out of
solution. Apparently this anhydride is, in this respect also, quite
different from the partly neutralised diphenylmethanedisulphonic acid.
2. Condensation with Sulphur Chloride
When sulphur chloride is allowed to act upon phenolsulphonic acid whilst
heat is applied, a yellowish-grey mass results, which dissolves in
water, forming a reddish-yellow solution. Neutralised to acidity 10, it
exhibits the following reactions:--
Gelatine----------------Precipitate.
Ferric chloride---------Deep blue coloration.
Lead acetate------------White precipitate, insoluble HNO_3.
Aniline hydrochloride---Precipitate.
Bromine water-----------No reaction.
The partly neutralised 2° Bé. solution of this product yielded a
reddish-grey coloured leather, the qualities of which were very similar
to that yielded by Neradol D.
3. Condensation with Phosphorus Compounds
Schiff's well-known synthesis, [Footnote: Liebig's _Ann_., 178, 173.]
in which phosphorus oxychloride interacts with phenolsulphonic acid,
yields a product which exhibits some tannin reactions, but which, when
acting on pelt, converts the latter into a leather which, when dried, is
very cracky. If, on the other hand, cresolsulphonic acid is condensed
with phosphorus oxychloride by heating the two together, products
eminently suitable for tanning purposes result. These products are
non-crystalline bodies easily soluble in water, and are coloured
bluish-violet by ferric chloride and precipitate gelatine. Solutions of
the free acids and acidified solutions of the salts convert pelt into
firm and white leathers possessing great softness and
pliability.[Footnote: Austr. Pat, 66,895.]
4. Condensation with Aldehydes
By treating phenolsulphonic acid with acetaldehyde in the usual way, a
viscous brown mass is obtained, which is very soluble in water, the
solution being of a brown colour. When brought to acidity 10, the
following reactions are exhibited by the product:--
Gelatine - - - Precipitate.
Ferric chloride - - Deep blue coloration.
Aqueous ammonia - - Cherry-red coloration.
Lead acetate - - - Yellowish precipitate, insoluble
HNO_3.
Aniline hydrochloride - - Yellow precipitate, soluble excess
aniline.
Bromine water- - - No reaction.
Tanning experiments with this substance yielded, even after extended
tannage, an undertanned leather, the surfaces being coloured brown, the
inner layers, however, white. Further neutralisation reduces the
tanning intensity of the product; the addition of sodium sulphate to the
original partly neutralised product hastened tannage, the leather,
however, possessing dark colour and being undertanned. The following
constitution may be ascribed to this product:--
OH OH
^ ---CH_2---CH_2--- ^
| | | |
| | | |
v v
HSO_3 HSO_3
If benzaldehyde is used in lieu of acetaldehyde for condensing
phenolsulphonic acid, a water-soluble product results, exhibiting
reactions similar to those of the acetaldehyde-condensation product. The
former product is more suitable as a tanning agent and yields a
reddish-brown rather firm and hard leather; it possesses the
constitution--
H
OH || OH
^ ____C____ ^
| | ^ | |
| | | | | |
v | | v
HSO_3 v HSO_3
For the purpose of condensing phenol with formaldehyde, it is not
essential to first convert the phenol into the water-soluble
phenolsulphonic acid, since it is possible to convert the condensation
products of phenol and its derivatives, which are soluble in alkali,
into water-soluble form by either heating the condensation products with
concentrated solutions of formaldehyde and neutral sulphites, or by
dissolving the condensation products in alkali and inducing reaction by
means of formaldehyde bisulphite. [Footnote: _Collegium_, 1913, 518,
324.] Highly concentrated solutions result, which may be concentrated
either as such or after the alkali present has been neutralised. The
sulphurous acid formed prevents oxidation of the product on
evaporation. A special advantage of this method of preparation is the
fact that sulphuric acid, which is but difficultly removed from the
end-product, is not employed at all.
The product thus obtained is a yellowish-white crumbly mass, which is
very soluble in water, forming a clear solution. The latter exhibits
the following reactions:--
Gelatine---------------Precipitate.
Ferric chloride--------Deep blue coloration.
Aqueous ammonia--------Cherry-red coloration.
Lead acetate-----------White precipitate, insoluble in
HNO_3.
Aniline hydrochloride--Precipitate.
Bromine water----------No reaction.
The product brought to acidity 10, yielded on analysis the
following figures:--
Tanning matters------------------ 25.2 per cent.
Soluble non-tannins-------------- 56.3 "
Insolubles----------------------- 0.0 "
Water---------------------------- 18.3 "
-------------
100.0 per cent.
Tanning experiments with this substance yielded white and soft leathers,
which were indistinguishable from those tanned with Neradol D.
A characteristic feature of this synthetic tannin is its behaviour in
concentrated form towards pelt, which is not attacked by it, but is
readily tanned even at such high concentrations. An explanation of this
is to be found in the large quantity of salts present in the product. A
disadvantage of this synthetic tannin is its complete incapability of
dissolving phlobaphenes, which is even so far extended as to precipitate
otherwise easily soluble tannins when adding it to solutions of the
latter in comparatively large proportions; here, again, the salts are
responsible for this behaviour, their large quantities effecting a
salting out of the natural tannins.
The class of aldehyde condensations also comprises that of inducing
condensation by means of sugars; if phenolsulphonic acid is heated with
glucose, a reddish-brown liquid results, which is soluble in water. The
solution exhibits reactions similar to those of Neradol D. It is,
however, not possible, by this method of condensation, to prepare as
highly concentrated products as is possible in the case of Neradol D,
since employing sugars as condensation agents means liberation of a
large volume of water. Analysis of this product, using the shake method,
gives a tannin content of 16.2 per cent; tanning experiments
demonstrated that the time of tannage, using a 2° Bé. solution, was the
same as that required by Neradol D, and yielded a leather, the surface
of which was reddish-grey, the inner layers being white, but which is
otherwise very similar to Neradol D tanned leather. [Footnote:
Austr. Pat, 69,375, 69,376, 69,377.]
Relatively to its capability of solubilising phlobaphenes, this product
exhibits similar properties to that obtained by merely heating
phenolsulphonic acid, to a slight extent only solubilising quebracho
extract, which, on diluting the mixture, is completely thrown out of
solution.
5. Condensation with Glycerol
Phenolsulphonic acid, when heated with glycerol, undergoes the process
of condensation, and forms a brown fluid, which, when brought to acidity
10, exhibits the following reactions:--
Gelatine-----------------Precipitate.
Ferric chloride----------Brown-black coloration.
Lead acetate-------------White precipitate, insoluble in
HNO_3.
Aniline hydrochloride----Slight precipitate.
Tanning experiments with this partly neutralised product resulted in a
very gradual conversion of the pelt into a greenish-grey coloured
leather; the colour, however, does not penetrate the pelt and is hence
caused by colloidally suspended impurities. If the solution is filtered
through a filter candle, a somewhat clearer solution results, but the
latter also tans very slowly and yields a brown coloured leather.
Analysis of the partly neutralised product reveals a tannin content of
17.6 per cent. A 2° Bé. solution of the non-neutralised product showed a
rapid tanning effect at first, when brought into contact with pelt, on
which it had a strong swelling effect, and to which it imparted a
greenish colour; the tanning effect, however, slowed down considerably,
after a few days, and the solution penetrated the pelt only very
gradually; this is probably due to the presence of large quantities of
colloidally suspended impurities, which, when the substance is partly
neutralised with the formation of salts of the sulphonic acids, are
brought into true solution and hence penetrate the pelt with greater
rapidity.
INDEX OF AUTHORS
Adler
Appelius
Ashmore
Bader
Badische Anilin u.(German abbreviation for "und") Soda-Fabrik
Baekeland
Baeyer
Berzelius
Biginelli
Boehringer & Sons
Bottinger
Braconnot
Buff
Caro
Chem. Fabrik Jucker & Co.
Chevreul
Dekker
Deutsch-Koloniale Gerb u. Farbstoff Gesellschaft
Deyeux
Dizé
Drabble
Edner
Elberfelder Farbenfabriken
Fahrion
Feist
Fischer, E.
Freudenberg
Froda
Gerhardt
Gesellschaft f.(German abbreviation for "für") Chem. Industrie, Basle
Graebe
Graham
Grasser
Hatchett
Heinemann
Herzig
Herzog
Hönig
Iljin
Immerheiser
Jennings
Kahl
Kauschke
Klepl
König
Kostanecki
Krafft
Krauss
Kunzemüller
Lauffmann
Liebig
Lipp
Lloyd
Löwe
Manning
Mauthner
Meunier
Michael
Mielke
Mitscherlich
Nierenstein
Paessler
Paternò
Payne
Pelouze
Perkin
Proust
Rapoport
Raschig
Reinsch
Resch
Russanow
Sabanajew
Sander
Scheele
Schiff
Schmidt
Schorlemmer
Seel
Seyewetz
Sisley
Skey
Stiasny
Strauss
Thuau
Tschirch
Vogel
Walden
Webster
Weinschenk
Wohl
Zacharias
A
Alcohol figure
Algarobilla
Alizarin
Alizarin yellow, in paste
Alkalies, reaction of, to Neradol D
Alum-neradol tannage
Alum tannage
Aminobenzene
Aminophenol, _p_-
Aniline dyes
Anthracene
Anthraquinone
Arylsulphaminoarylsulphonic acids
Arylsulphoxyarylsulpho acids
B
Bakelite
Bakelite solution
Benzoylamino 6-chloranthraquinone
Benzylsulphanilate sodium
Bismuth salts
Bleaching method for leather with Neradol D
Bloom
Bromo-[Greek: b]-naphthol
Bromonitrophenol
Bromophloroglucinol
Bromosalicylic acid
Bromotrinitrophenol
C
Carbazole
Carbomethoxyhydroxybenzoic acid,
Carbomethoxyhydroxybenzoic acid chloride,
Catechine
Catechol
Cerium salts
Ceruleoellagic acid
Cesium salts
Chestnut wood extract
Chloronaphthalenesulphonic acid
Chlorophenol
Chrome-Neradol D tannage
Chrome salts
Chrome tannage
Coal, bituminous
Coffee tannin
Combination tannage with Ordoval
Combination tannage with Neradol D
Condensation by heat
Condensation methods
Condensation with aldehydes
Condensation with glycerol
Condensation with phosphorus compounds
Condensation with sulphur chloride
Copper salts
Corinal
Cresol
Cresol-_p_-sulphonic acid, _o_-
Cresolsulphonic acid
Cresotinic acid
D
Depsides
Detannisation with hide powder
Diaminoanthraquinone
Diaminonaphthylmethanedisulphonic acid
Dianilinoquinone
Dibenzopyrrol
Di-[Greek: b]-oxynaphthoic
Di-[Greek: b]-resorcylic acid
Dichloranthraquinone
Dichloronaphthylmethanedisulphonic acid
Dicresylmethanedisulphonic acid
Dicresylmethanedisulphonic acid purified electro-osmotically
Dicresylmethane sulphonate sodium
Didepsides
Didymium salts
Diferulic acid
Digallic acid
Digallic acid, [Greek: b]-
Digallic acid, inactive
Digallic acid, _m_-
Digalloylleucodigallic acid anhydride
Digentisinic acid
Dihydric alcohols, aromatic
Dihydroxybenzene, _m_-
Dihydroxybenzene, _o_-
Dihydroxybenzene, _p_-
Dihydroxybenzenes
Dimethylaniline
Dimethylellagic acid
Di-_m_-oxybenzoic acid
Dinaphthylmethanedisulphonic acid
Dinitronaphthylmethanedisulphonic acid
Di-_o_-cumaric acid
Diorsellic acid, _o_-
Diorsellic acid, _p_-
Dioxyellagic acid
Dioxynaphthylmethanedisulphonic acid
Dioxytoluic acid
Diphenylmethane
Diphenylmethanedisulphonic acid
Di-_p_-hydroxybenzoic acid
Diprotocatechuic acid
Disalicylic acid
Disyringic acid
Dithionaphthylmethanedisulphonic acid
Dividivi
Dividivi tannin
Dixylylmethanedisulphonic acid
E
Electro-chemical behaviour of Neradol D
Electro-osmosis of Neradol D
Ellagic acid
Ellagitannic acid
Empirical formula of tannin
Erythrine
Esco-extract
Ester formula of tannin
Ethyl acetate figure
F
Fat-Neradol D tannage
Feruloyl-_p_-oxybenzoic acid
Flavellagic acid
Fluorene
Formaldehyde
Formaldehyde tannage
G
G-acid
Gallate ethyl
Gallic acid
Galloflavine
Galloyl-_p_-hydroxybenzoic acid
Galls, oak
Gall tannin
Generator tar
Guaiacol
H
Halogens
Hepta-[tribenzoyl-galloyl]-_p_-iodophenylmaltosazone
Hexahydroxyaurinecarboxylic acid
Hexoxyanthraquinone
Hexoxydiphenyl
Hexoxydiphenyldicarboxylic acid
Hexoxydiphenylmethanedicarboxylic acid
Humic acid
Hydrolysis of tannins
Hydroquinone
Hydroxybenzoate sodium, _m_-
Hydroxybenzoate sodium, _p_-
Hydroxybenzoic acid, _p_-
Hydroxybenzoic acid
Hydroxy-cymenes
I
Indophenol reaction
Iron, reaction of, to Neradol D
Iron salts
K
Ketone formula of tannin
L
Lanthanum salts
Lead salts
Leather analysis in presence of Neradol D
Lecanoric acid
Leucodigallic acid
Leucoellagic acid
Leucotannin
Lignite
Luteic acid
M
Malletto tannin
Mangrove tannin
Melangallic acid
Mercury salts
Metellagic acid
Methylamino-4-bromanthraquinone
Methylenedinaphthol
Methylenedisalicylic acid
Methylenedisalicylic acid, brominated
Methylenedisalicylic acid, iodised
Methylisopropylphenanthrene
Methylotannin
Molybdenum figure
Monochloro-_p_-dihydroxybenzene
Mud
Myrabolams
Myrabolams, tannin
N
Naphthalenesulphonic acid, [Greek: b]-
Naphthol, [Greek: a]-
Naphthol, [Greek: b]-
Naphthol-[Greek: a]-methanesulphonic acid
Naphtholdisulphonic acid
Naphtholmonosulphonic acid
Naphtholsulphonic acid, [Greek: a]-
Naphtholsulphonic acid, [Greek: b]-
Neodymium salts
Neradol D
Neradol D tannin
Neradol N
Neradol ND
Neradol ND, neutral
Nitronaphthalenesulphonic acid
Nitrophenol, _o_-
Nitrosodimethylaniline
Non-tannins
Novolak
O
Oak bark
Oak bark tannin
Official method of tannin analysis
Orcinol
Ordoval G
Orsellic acid
Orsellinoyl-_p_-oxybenzoic acid
Oxyanthraquinone
Oxyazo reaction
Oxybenzoyl-_m_-hydroxybenzoic acid
Oxybenzoyl-_p_-hydroxybenzoic acid, _m_-
Oxybenzoylsyringic acid
Oxynaphthoyl-_p_-hydroxybenzoic acid, _a_-
Oxynaphthylmethanesulphonic acid
Oxyphenylmethanesulphonic acid
Oxyquinoline
P
PATENTS--
_Austrian_
58,405; 61,057; 61,061;
64,479; 66,895;
68,796; 69,194;
69,375; 69,376;
69,377; 70,162
_German_
72,161; 111,408; 112,183;
132,224; 181,288;
184,449; 200,539;
206,957; 211,403;
262,558; 282,313;
286,568; 290,965;
291,457; 293,042;
293,640; 293,693;
297,187; 297,188;
300,567; 303,640;
305,516; 319,713;
320,613
_Swiss_
78,282; 78,797; 79,139
_U.S.A._
1,639,174
Peat
Pelts
Pelts, action on, of Neradol D
Penta-[_p_-hydroxybenzoyl] glucose,
Penta-[_p_-methyl-_m_-digalloyl]-glucose
Penta-[pyrogalloylcarboyl]-glucose
Pentacetylleucotannin
Pentacetyl-_m_-digallic acid
Pentacetyl tannin
Pentadigalloylglucose
Pentagalloylglucose
Pentagalloylglucoside
Pentamethyldigallic acid, methyl ester
Pentamethyl-_m_-digalloyl chloride,
Pentamethyl-_m_-digallic acid
Pentamethyl-_m_-digallic acid methyl ester
Pentamethyl-_p_-digallic acid
Pentamethyl-_p_-digallic acid methyl ester
Pentamethoxybiphenylmethylolide carboxylic acid methyl ester
Pentoxybiphenylmethylolide
Pentoxybiphenylmethylolide carboxylic acid
Phenanthraquinone
Phenolsulphonate sodium
Phenolsulphonic acid
Phenolsulphonic acid anhydride
Phenol, tautomeric
Phenylcarboxylic acid
Phenylhydrazine derivatives of tannin
Phenylhydrazine ellagic acid
Phlobaphene
Phlobaphene-solubilising action of neradols
Phloroglucinol
Phthalic acid
Pickling
Picric acid
Platinum salts
Polydepsides
Polydigalloylleucodigallic acid anhydride
Polyhydroxybenzenes
Pomegranate
Preparation of tannin infusion
Properties of leather tanned with Neradol
Protocatechuic acid
Protocatechuyl-_p_-hydroxybemoic acid
Pseudo-tannage
Purpuro tannin
Pyrogallol
Pyrogallic acid
Pyrogalloylcarboyl-_p_-oxybenzoic acid
Pyruvic acid
Q
Quinazarene
Quinoline
Quinone
R
R-acid
Reaction, Procter-Hirst
Reagents for Neradol D tannage
Resites
Resitol
Resols
Resorcinol
Resorcylic acid, [Greek: b]-
Retene
Rosins, acid
Rosolic acid
Rufigallic acid
S
S-acid
Salicylic acid
Salicylic acid phenyl ester
Salicyl-_p_-hydroxybenzoic acid
Salol
Silver oxide
Solution salt
Solvenol
Structure of tannin
Sulphinic acid
Sulphite cellulose extract
Sulphite lye
Sulphonamide
Sulphonic acids, aromatic
Sulphonic chloride
Sulphur
Sulphur tannage
Sulphuric acid-free Neradol D
Sulphuric acid in leather
Syringoyl-_p_-hydroxybenzoic acid
T
Tannin
Tannin action, real
Tannin analysis
Tanning matters
Tannin molecule
Tannin, pure
Tannophor
Test tannage
Tetradepsides
Tetragalloyl-[Greek: a]-methylglucoside
Tetramethylellagic acid
Tetroxydiphenyldimethylolide
Thionaphtholsulphonic acid
Thiosulphonic acid
Thorium salts
Thymol
Toluidoanthraquinone, l-_m_-
Total solids
Total solubles
Tribromophenol
Tribromopyrogallic acid
Tricarbomethoxygalloyl chloride
Tridepside
Trihydroxybenzenes
Trinitrophenol
Triphenylmethane
V
Valonea
Vanadium salts
Vanillic acid
Vanilloyl-di-_p_-oxybenzoyl-_p_-hydroxybenzoic acid
Vanilloyl-_p_-hydroxybenzoic acid
Vanilloyl vanillin
X
Xanthenes
Z
Zinc salts
Zirconium salts