Chapter VIII: Part II: Synthetic Tannins: Their Industrial Production and Application (1)

With regard to their _industrial production_, but few synthetic tannins are, to-day, of practical and commercial interest. In addition to simplicity in the method of manufacture a certain degree of purity of the raw materials constitutes the criterion of their suitability. The methods of manufacture, of which nearly all are the property of the B.A.S.F., have been so worked out that the production of synthetic tannins presents no difficulties on a practical scale. Cresols, naphthalenes, and higher hydrocarbons are used as starting materials in the production of synthetic tannins; the former substances or their oxidation products are sulphonated by means of concentrated sulphuric acid, and the tanning matter produced by condensing the sulphonic acids with formaldehyde. The crude synthetic tannin thus obtained has yet to be diluted and partly neutralised before it can be applied in practice, and this is carried out by mixing the crude product with strong caustic lye. By these means the high acidity is reduced to a suitable degree learned from experience on the one hand; on the other hand, the salts of the sulphonic acids form valuable components of the commercial synthetic tannins.

The first product placed on the market was named _Neradol D_; this represents the condensation product of cresolsulphonic acid. The second synthetic tannin was _Neradol N_, which represents the condensation product of naphthalenesulphonic acid; when diluted and neutralised to the same extent as is done in the case of Neradol D, the product is named _Neradol N D_. The latest synthetic tannin has been called _Ordoval G_, the starting material of which is a still higher hydrocarbon.

The tannoid-chemical properties of these synthetic tannins have been exhaustively determined by the author, who employed Neradol D, which is most suitable for such a purpose, and the investigations relating to it will now be treated fully in the following chapters. The two other synthetic tannins exhibit very similar properties, but their few characteristics shall be shortly dealt with.

The condensation product obtained by the method described on p. 55 forms a viscous, dark coloured mass, the analysis of which by the shake method gives the following figures:-

Tanning matters 62.6 per cent. Non tannins 6.4 " Insolubles 0.0 " Water 31.0 " --------------- 100.0 per cent.

Acidity: 1 gm. = 40 c.c. N/10 NaOH.

According to its chemical constitution, this product may be considered to be dinaphthylmethanedisulphonic acid.

Samples of this crude, strongly acid material were partly neutralised, and the following figures obtained on analysis:--

Acidity. Tanning Soluble Water.
Matters. Non-tans.

Per Cent. Per Cent. Per Cent. 1 gm. = 35 c.c. N/10 NaOH 61.8 7.0 31.2 1 " = 30 " " 58.9 7.1 34.0 1 " = 25 " " 50.1 7.9 42.0 1 " = 20 " " 42.2 8.9 48.9 1 " = 15 " " 37.4 10.4 52.2 1 " = 10 " " 31.6 13.6 54.8 1 " = 5 " " 26.3 16.6 57.1

Experimental tanning tests which were carried out with the various partly neutralised samples yielded leathers which, on an average, were nearly white, but which in comparison with a leather tanned with Neradol D appeared rather more greyish and were much harder.

A solution of the half-neutralised substance (1gm. = 20 c.c. N/10 NaOH) gives the following reactions:---

Gelatine--Precipitate, partly soluble in excess tannin solution. Ferric chloride-----No coloration. Barium chloride-----Precipitate, insoluble HNO_3. Bromine water-----No reaction. Silver nitrate-----No reaction. Aniline hydrochloride----Precipitate, dissolves when solution is heated.

This condensation product is very soluble in water, but insoluble in most solvents, excepting methyl and ethyl alcohols. The above reactions show the similarity of this dinaphthyl derivative to the dicresyl derivative, and the absence in the former of characteristic reactions with iron salts is mainly accounted for by its lack of phenolic groups. The absence of this reaction does not, of course, influence the tannoid character of dinaphthylmethanedisulphonic acid in the least, and is of no importance in practice, since the various stages of tannage may be demonstrated by means of a solution of indigotine.

From a technical point of view the absence of this reaction is advantageous to this extent, that it eliminates the exceedingly great care to avoid the contact of tan liquors and tanned pelt with iron particles which has to be observed when tannins of phenolic character are employed.

In a chemical and technological evaluation of this tanning matter, all those details apply which will be described when discussing Neradol D. The most important advantage possessed by this tanning matter, from a commercial point of

view, is the lower price which it owes to the greater ease with which naphthalene may be obtained.

By treating the non-condensed crude product with barium chloride, a product completely devoid of sulphuric acid is easily obtained; the contents of sulphuric acid calculated as BaSO_4 is about 9.5 per cent. This value is higher than that found by Neradol D, and may be explained by the fact that a slight excess of sulphuric acid is necessary for the preparation of [Greek: b]-naphthalenesulphonic acid.

Comparative tanning tests using products containing sulphuric acid and products free from sulphuric acid (neutralised to the same degree of acidity) yielded leathers which were very similar; the liquor containing no sulphates yielded slightly softer leather than that obtained from a liquor containing sulphates.

An experiment was also carried out, using a liquor containing the tannin completely neutralised with caustic soda and subsequently acidified with acetic acid till the acidity of 1 gm. = 10 c.c N/10 NaOH; here, again, no essential difference could be detected in the leather as compared with that from a liquor containing sulphates.

One of the most striking properties of this tanning matter is its solubilising effect on natural tannins and the phlobaphenes; this property may mainly be compared to the similar one of other condensed sulphonic acids in their behaviour towards natural tannins.

If, therefore, natural tannins are mixed with this product and the solution used for tanning purposes, the resultant leather will possess a dark colour owing to the presence of solubilised phlobaphenes; if, on the other hand, a dark coloured leather, which has been tanned with natural tannins, is washed over with a 5° Bé solution of this synthetic tannin, or immersed for some time in the solution, the leather assumes a lighter colour owing to the phlobaphenes being dissolved and removed from the leather by the synthetic tannin.

The presence of Neradol ND in leathers is detected by methods to be described under Neradol D (_cf_. p. 108). The oxyazo reaction only succeeds when the solution has been boiled with a few drops of hypochlorite solution, quickly cooled and excess of ammonia added. When applying the indophenol reaction, the solution must be treated as follows: 3-4 drops of hypochlorite solution is added, and the solution heated for a short time; or 5-6 drops hypochlorite solution may be added, and the solution left for some time, in which case the heating may be omitted. The solution is then made distinctly ammoniacal, 1-2 drops of dimethyl-_p_-phenylenediamine solution and a layer of alcohol poured on the top. In most cases a blue coloration will appear; the addition of 1-2 drops of potassium ferricyanide solution with formation of a blue coloration indicates the presence of Neradol ND without fail.

The fact that a product possessing tanning properties may be obtained by condensing [Greek: b]-naphthalenesulphonic acid makes it interesting to investigate the behaviour of a non-condensed [Greek: b]-naphthalenesulphonic acid towards pelt. The following solutions were allowed to act upon pelt for twelve days:--

(1) Concentrated solution of [Greek: a]-naphthalenesulphonic acid (10° Bé). (2) " " [Greek: b]- " " (6° Be.) (3) " " 2,7- " " (18° Bé.).

Solution 1 swells the pelt to a considerable extent without, however, solubilising it. Solution 2 produces a similar effect. Solution 3 dissolves the pelt appreciably on the first day; after six days, solubilisation is complete. The reason of this different behaviour of the mono- and disulphonic acids is mainly to be sought in their difference of solubility; the monosulphonic acids are not very soluble, and are only capable of giving solutions measuring 10° and 6° Bé, respectively, whereas the disulphonic acid yields an 18° Bé solution, in addition to which the much higher acidity of the latter quickly gelatinises the pelt.

As regards the capability of the naphthalenesulphonic acids of dissolving phlobaphenes, the following results were obtained:--solid Argentine quebracho extract was mixed with--

5 percent, [Greek: a]-naphthalenesulphonic acid: opaque sol., large quantity of insolubles. 10 " " " lesser " " 20 " " " no insolubles. 30 " " " " 5 " [Greek: b]-naphthalenesulphonic acid: opaque sol., lesser quantity of insolubles. 10 " " " " 20 " " " clear solution, no insolubles 30 " " " " 5 " 2,7-naphthalenedisulphonic acid: opaque sol., large quantity of insolubles. 10 " 2,7 " " as above. 20 " 2,7 " " slightly opaque, some insolubles. 30 " 2,7 " " nearly clear solution, no insolubles.

It is hence clear that the [Greek: b]-sulphonic acid possesses phlobaphene-solubilising qualities greater than those of the [Greek: a]-sulphonic acid or the disulphonic acid; the Greek: b]-sulphonic acid was therefore made the subject of Ger. Pat., 181,288 (8th February 1917).

The synthetic tannin, _Ordoval G_, is the formaldehyde condensation product of higher hydrocarbons (mainly _retenes_), and is a partly neutralised product containing no sulphuric acid. The author's analysis gave the following figures:--

Tanning matters 10.7 per cent.
Soluble non-tannins 16.4 "
Insolubles 0.0 "
Water 73.0 "

Acidity: 1 gm. = 4 c.c. N/10 NaOH.
Density: 23° Be.

Ordoval G is completely soluble in water and glacial acetic acid. Only its organic constituents are soluble in alcohol, ethyl acetate, and acetone, whereby a dark coloured crystalline mass separates. Ordoval G is insoluble in benzene.

The aqueous solution of Ordoval G gives the following reactions:--

Gelatine Moderate flocculent precipitate. Ferric chloride Darkish coloration. Potassium dichromate No reaction. Aniline hydrochloride Dark brown precipitate. Formaldehyde hydrochloric acid No precipitate. Bromine water No reaction. Zinc acetate Very slight opalescence. Barium chloride Slight opalescence.

Its capability of solubilising and consequent saving of natural tannins is shown by the fact that 100 kilos of vegetable tanning material may be substituted by 40 kilos of Ordoval G and the material in question in order to obtain the entire tanning intensity of the latter.

In one respect--that of its salts--Ordoval G differs from the Neradols; whereas the chromium and aluminium salts of the latter possess no such tannoid properties as will make the resultant leather exhibit any of the characteristics of either tannage, it is possible to carry out combined tannage with a mixture of Ordoval G and metallic salts. Tanning experiments carried out with the chromium, iron, aluminium, and calcium salts of Ordoval G yielded leathers which possessed proportionate characteristics of either kind of tannage to the extent to which either material was present. This combination tannage seems to be assured of a great future; especially may a combination tannage of iron salts and Ordoval G eventually entirely replace chrome tannage.

The detection of Ordoval G in leather is carried out as follows: 10 gm. of leather are boiled with 150 c.c. of acetic acid, a solution of 25 gm. of CrO_8 in 25 c.c. of a 50 per cent, solution of acetic acid gradually added, and the mixture boiled for three hours, till the leather is decomposed and the solution has assumed a brown instead of the original light yellow colour. The solution is then evaporated, the residue dissolved in 600 c.c. hot water, and the chromium precipitated with a 40° Bé. solution of caustic soda. The solution is filtered and cooled, and a little hydrosulphite is added to 20 c.c. of the cold alkaline filtrate; in the presence of Ordoval G, a red colour will appear (oxanthranolsulphonic acid).

Brief mention must be made of the so-called _Corinal_ [Footnote: Swiss Pat, 78,282, 78,797, 79,39.] a synthetic tannin placed upon the market by Chem. Fabrik Worms A.-G., in Worms-on-the-Rhine. It is a viscous, brown fluid, containing the aluminium salts of the tannoid acids. The latter are formaldehyde-condensation products of sulphonated tar oils, or the hydroxylated derivatives of the latter. The density being 33° Bé, it contains 28.1 per cent. tanning matters, 13 per cent. soluble non-tannins, and 10.8 per cent. inorganic matter (3.2 per cent. Al_2O_3 and 7.6 per cent. Na_2SO_4.

A similar product, containing chrome salts as base, is the so-called ESCO-EXTRACT, [Footnote: Schorlemmer, _Collegium_, 1917, 124] manufactured by the Chem. Fabrik Jucker & Co. in Haltingen (Baden). This product is a dark, reddish-brown fluid, possessing acid reaction, which strongly precipitates gelatine. Analysed by the filter method it contains 12-15 per cent. tanning matters, 17-20 per cent. soluble non-tannins, and 18 per cent. ash, of which 3 per cent. is Cr2O_3. This synthetic tannin may be employed alone or in conjunction with other tannins, and yields a leather similar to that obtained by chrome tannage.

A. Condensation of Free Phenolsulphonic Acid

In practice, the results of condensing phenolsulphonic acid with formaldehyde are manifold, according to whether these materials are used in their concentrated or dilute state; whether they interact in the cold or when heated; or whether their interaction is gradual or rapid.

1. If a moderately dilute solution of phenolsulphonic acid (1:1) is mixed with one-sixth of its volume of a dilute formaldehyde solution (1 part 30 per cent. HCHO solution plus 3 parts of water) in the cold, with continuous stirring, the solution remains clear and assumes a brown colour. When left several hours, a light, white flocculent precipitate deposits, which increases in quantity on diluting with water. The solution precipitates gelatine; the flocculent precipitate is easily soluble in hot caustic soda solution, and, when subsequently neutralised with acetic acid, precipitates gelatine.

If equal parts of dilute phenolsulphonic acid and dilute formaldehyde (concentrations as above) are gradually mixed in the cold, whilst stirring, the mixture soon becomes opalescent, and a flocculent deposit separates after eighteen to twenty-four hours.

These experiments carried out on the water bath immediately yield opalescent liquids, from which an insoluble, brown, gluey, and very sticky mass separates after twenty-four hours; the latter is sparingly soluble in alkalies, partly so in organic solvents.

2. If a moderately dilute solution of phenolsulphonic acid (1:1) is gradually mixed with one-sixth of its volume of a concentrated (30 per cent.) formaldehyde solution in the cold, whilst stirring, slight opalescence immediately results, and a flocculent deposit separates after about twenty minutes, which gradually increases in quantity during the next few hours. If the volume of formaldehyde is increased to the same as that of phenolsulphonic acid solution, the flocculent deposit immediately separates, and after twenty-four hours a brown, gluey, and very sticky mass--of the same solubility as that described in the previous experiment--is to be found at the bottom of the vessel used.

It should be noted that in both these experiments with concentrated formaldehyde solution a slight increase in temperature occurs concurrently with the process of condensation. If the experiments are carried out on the water bath, a gelatinous mass is instantly formed, which assumes the colours of grey, dirty light violet and dark violet, in the order named, and which, whilst left several hours--or when heated on the water bath--is suddenly converted into the insoluble, brown, gluey mass above referred to.

3. If, for the purpose of condensation, phenolsulphonic acid to which 10 per cent, of water has been added, is employed, the reaction proceeds very quickly and energetically. If one-sixth of its volume of formaldehyde (1:3 of the 30 per cent. solution) is added drop by drop to a cold solution of phenolsulphonic acid, a reddish, milky solution results, which assumes a slightly lighter colour on addition of more formaldehyde and deposits an insoluble flocculent precipitate. If the solution is kept below 45° C., by artificial cooling, the light colour is maintained, but a gelatinous precipitate is soon formed, the viscosity of which increases on stirring, and finally is converted into an insoluble, tough, gummy mass. If, on the other hand, the mass is heated at the beginning of the reaction, or if the amount of formaldehyde is increased and the mass cooled during reaction, effervescence occurs, and a cheesy, dirty-coloured mass results, which, on cooling, rapidly becomes solid and yields a very firm, elastic, rubbery mass, which is absolutely insoluble in water.

4. The condensation proceeds exceedingly violently when concentrated phenolsulphonic acid is acted upon by one-sixth of its volume of formaldehyde. If the latter is firstly added drop by drop to the phenolsulphonic acid, a gel immediately results, the temperature of which quickly increases on further addition of formaldehyde and suddenly boils over, yielding a reaction product which, when cooled, forms a dirty violet, firm, elastic, and rubbery mass, insoluble in alkalies and hardly affected by organic solvents.

Finally, if the amounts of concentrated phenolsulphonic acid and formaldehyde stated above are mixed, strong effervescence occurs and heat is evolved, and a dirty blackish-violet mass is instantly formed which, on cooling, yields a rather brittle, hard product insoluble in water.

5. Totally different end-products are, however, obtained when the addition of formaldehyde (30 per cent.) in the proportion of one-sixth of the volume of dilute phenolsulphonic acid (1 plus 9 aq.) to the latter is extended over several hours. In this case a slightly opalescent liquid is obtained which, when left twelve hours, is transformed into a brown mass soluble in water, which strongly precipitates gelatine and possesses tanning properties. Hence direct tannoid substances are obtained by this method of condensation.

Whereas no direct tanning experiment can be carried out with the insoluble compact mass obtained in the preparations described above on account of their absolute insolubility, it is still possible to carry out tanning experiments with opalescent colloidal solutions in the following ways:--

(a) If a bated pelt is immersed in a liquid containing a condensation product obtained by gradually mixing a moderately dilute solution of phenolsulphonic acid and a dilute solution of formaldehyde, the pelt is rapidly tanned on the surface. Complete penetration of the substance does not occur even after several days, since the strong acidity of the solution causes a strong swelling of the pelt.

(b) If a pelt is shaken for six hours in a shaking apparatus containing the liquid mentioned under (a), tannage again only takes place on the surface, penetration being impeded by the strong swelling effect of the liquid. Repetition of the latter two experiments, with the addition of 15 per cent, common salt, increases the tanning effect to some extent; the pelt, however, is not tanned through, but the non-tanned layers may be clearly seen to be pickled.

The tanning effects described above are only exhibited when the colloidal tan-liquor is present in great excess over the pelt, since the former obviously only contains small amounts of tanning matter, and even the presence of common salt does not bring about complete tannage of the pelt.

In order to prove the presence of "tanning matters" in the liquid described above, several freshly prepared samples of the latter were analysed by the shake method of analysis without being first filtered and the following figures obtained:--

1. 2. 3. 4.
Per Cent. Per Cent. Per Cent. Per Cent.
Tanning matters 6.4 7.7 8.2 9.1

Soluble non-tannins 15.2 17.4 14.5 11.8

These condensation products suspended in water all precipitate gelatine strongly and leave behind a perfectly clear liquid. In all cases, an intense blue colour was obtained on adding ferric chloride, a slight precipitate only was obtained with aniline hydrochloride, and bromine was rapidly absorbed with the separation of an insoluble white deposit.

The condensation products obtained by the interaction of dilute solutions of phenolsulphonic acid and formaldehyde at moderately high temperature, which form slimy masses and are insoluble in water, are soluble in alcohol. An alcoholic solution of such a product was used in a tanning experiment, and a piece of pelt immersed in the solution was tanned through in a few days; the resultant leather being rather firm, springy, and slightly hard, and the colour was a light brownish-grey.

All those condensation products which are easily or partly soluble in alcohol dissolve in caustic soda, sodium carbonate, in some cases also in borax and sodium sulphite. They are rendered soluble with greater ease when the _freshly prepared_ solution is heated on the water bath with the alkali; the alkaline solution, neutralised as far as is possible with acetic acid, yields light brown coloured solutions, the tanning effects of which have proved very satisfactory. Leathers tanned in such solutions, however, are rather empty and hard, possess but little resilience and an uneven, dirty greyish-brown colour.

A sample of such a product, as nearly as possible neutralised with acetic acid, contained 14.8 per cent. tanning matters, by the shake method of analysis.

B. Condensation of Partly Neutralised Phenolsulphonic Acid

Attempts were made at condensing partly neutralised phenolsulphonic acid; the latter was obtained by mixing equal quantities of phenolsulphonic acid and sodium phenolsulphonate (prepared by exactly neutralising phenolsulphonic acid with a concentrated solution of caustic soda).

The consequent dilution and decrease in acidity, however, considerably diminished the velocity of the reaction. Hence, if the half-neutralised Solution A1 (_cf_. p. 98) is diluted with water, taking equal volumes, and one-sixth of the volume of dilute formaldehyde (1:3) gradually added in the cold, condensation is not induced. When heated several hours an opalescent liquid results from which, however, no flocculent deposits separate when left for some time. Using a concentrated solution of formaldehyde (Experiment A2, p. 98) in the cold produces no reaction, but after heating for a time an opalescent liquid is obtained. Both liquids give only slight precipitates with gelatine. Excess formaldehyde does not influence the reaction.

A repetition of Experiment A3 (_cf_. p. 99), using the above half-neutralised phenolsulphonic acid, similarly required heat to induce condensation, when a milky liquid of light reddish colour resulted.

Whereas the addition of formaldehyde to non-neutralised concentrated phenolsulphonic acid caused violent reaction, this proceeded very slowly in the case of half-neutralised phenolsulphonic acid, resulting in the formation of a semi-solid mass, which on heating became more viscous, and finally, when left twenty-four hours, became a solid, compact, insoluble mass possessing a dirty light violet colour.

Tanning experiments with these opalescent solutions proved them to exert a rapid penetration on the surface, complete tannage, however, taking place after eight days only, when a flat, greyish-coloured and rather hard leather resulted.

C. Condensation of Completely Neutralised Phenolsulphonic Acid

If concentrated phenolsulphonic acid is gradually neutralised with concentrated caustic soda solution till the former is faintly alkaline, the sodium salt thus obtained is not so easily condensed with formaldehyde as is the case with the free acid.

1. If formaldehyde is gradually added to the neutralised phenolsulphonic acid in the cold, opalescence immediately results; on addition of water, the liquid assumes a milky appearance. On adding gelatine to this liquid, a slimy precipitate is thrown down, leaving a slightly opalescent liquid.

2. If formaldehyde is added to neutralised phenolsulphonic acid whilst it is heated on the water bath, a slimy mass instantly separates, which on cooling solidifies and forms a greyish-blue brittle mass, insoluble in water and but sparingly soluble in alcohol; the alcoholic solution is capable of converting pelt into leather.

The filtrate from the solidified mass strongly precipitates gelatine, whereas the insoluble condensation product is soluble in caustic soda; this alkaline solution also precipitates gelatine and the addition of acetic acid transforms the mixture into the gel state.

If the insoluble condensation product is dissolved in warm concentrated sulphuric acid, the solution remains clear upon the addition of water, but does not precipitate gelatine. If, finally, this solution is neutralised with caustic soda, the solution remains clear and precipitates gelatine strongly.

D. Condensation of Cresolsulphonic Acid

Experiments were carried out with the object of condensing _o_-, _m_-, and _p_-cresolsulphonic acids with formaldehyde in various ways; no essential differences could be detected as regards the mode of reaction or the properties of the intermediary and end-products as compared to those of phenolsulphonic acid. Similarly, condensation of different samples of crude cresol containing varying quantities of _o_-, _m_-, and _p_-cresol did not yield end-products sufficiently different to justify describing them in detail.

E. Relative Behaviour of an Alkaline Solution of Bakelite and Natural Tannins

Phenolsulphonic acid was condensed with a little formaldehyde, and the reddish pasty condensation product dissolved in caustic soda. This alkaline solution of bakelite was exactly neutralised with acetic acid and mixed with strong solutions of an untreated quebracho extract. It was observed that the solubility of the quebracho extract was not increased by this treatment, but the faintly acidic character of the natural tannin caused the bakelite to be thrown down as an insoluble precipitate.

Crude phenolsulphonic acid, when added to a solution of the quebracho extract referred to, does not increase the solubility of the latter, which even deposits considerable amounts of insoluble tannin particles.

Quite different properties are exhibited by sodium phenolsulphonate, which completely converts quebracho tannin into a water-soluble substance, the aqueous solution of which deposits no insolubles. The partly neutralised condensation product of phenolsulphonic acid and formaldehyde exhibits similar properties [Footnote: Grasser, _Collegium_, 1913, 521, 478.] (see later).

F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat., 291, 457; Austr. Pat., 61, 057.]

Neradol D is a viscous liquid, measuring about 33° Bé., which is similar to extracts of natural tannins. One of its characteristics is its phenolic odour; it is completely soluble in water, forming a clear, semi-colloidal solution, but is insoluble in all organic solvents with the exception of alcohol, glacial acetic acid and ethyl acetate, which dissolve all but its inorganic constituents. The latter owe their presence to the neutralisation of the crude Neradol with caustic soda, and are composed of sodium salts of the sulphonic acid in addition to Glauber salts.

The aqueous solution of Neradol D shows properties similar to those exhibited by solutions of natural tannins and reacts as follows:--[Footnote: Grasser, _Collegium_, 1913, 520, 413.]

Methyl orange Acid reaction. Barium chloride White precipitate, insoluble in HNO_3. Ferric chloride Deep blue coloration. Silver nitrate Slight opalescence. Bromine water No precipitate. Formaldehyde hydrochloric acid No precipitate. Gelatine Complete precipitation. Aniline hydrochloride Strong precipitate.

The reactions with ferric chloride and gelatine should be especially noted, since they are analogous to those given by natural tannins. On the other hand, the reactions with BaCl_2, bromine water and formaldehyde hydrochloric [Footnote: Stiasny carries out the reaction with formaldehyde-hydrochloric acid as follows:--50 c.c. of the tannin solution, plus 5 c.c. concentrated hydrochloric acid and 10 c.c. formaldehyde (40 per cent.) are heated under reflux condenser for ten minutes; most natural tannins are completely precipitated (_Collegium_, 1906, 435; 1907, 52 _et_ 188).] acid prove the different chemical composition of Neradol D as compared to that of the natural tannins.

The fact that a positive reaction is given with aniline hydrochloride [Footnote: This reaction is carried out as follows:--5 c.c. of the tannin solution to be examined (about 4 gm. tanning matter per litre) are shaken violently in a test tube with 0.5 c.c. aniline and 2 c.c. concentrated HCl added. All natural tannins are unaffected by this treatment, ligninsulphonic and other sulphonic acids cause opalescence. _Note_.--Employing formic acid in lieu of hydrochloric acid (Knowles) renders the reaction no more reliable.--_Transl_.] is very puzzling; none of the natural tannins are precipitated by this reagent, but only sulphite cellulose on account of its content of ligninsulphonic acid. One is justified in assuming that there is at least some connection between the constitution of ligninsulphonic acid and that of dicresylmethanedisulphonic acid.

Stiasny [Footnote: _Collegium_, 1913, 516, 142.] recommends the following reaction for the detection of and differentiation between Neradol D and wood pulp extract:--10 c.c. of a 5 per cent. solution of the extract to be analysed are violently shaken with 1-2 drops of a 1 per cent. alum solution and about 5 gm. of ammonium acetate. If only Neradol D is present no precipitate separates even after twenty-four hours, but if wood pulp be present, a precipitate is thrown down in a quantity corresponding to the amount of wood pulp present.

The official analysis gives the following figures: [Footnote: Grasser, _loc. cit._]

Tanning matters 32.5 per cent.
Soluble non-tannins 33.0 "
Insolubles 0.0 "
Water 34.5 "
-------------
100.0 per cent.

Ash 17.0 "

Acidity: 1 gm. = 10 c.c. N/10 NaOH.
Density: 33º Bé.

A comparison of its quantitative analysis to that of a natural tanning extract is illustrated by the following figures of a chestnut and a quebracho extract of same density (26º Bé):--

Chestnut Quebracho
Per Cent. Per Cent.
Tanning matters 32.0 34.0
Soluble non-tannins 12.0 8.0
Insolubles 1.5 2.0
Water 54.5 56.0
----- -----
100.0 100.0

Ash 0.4 2.0

This comparison shows that extracts of natural tannins firstly contain certain amounts of "insolubles," whereas Neradol is completely soluble in water, forming a clear solution; secondly, natural tanning extracts contain smaller quantities of soluble non-tannins, consisting of colouring matter and sugars, in addition to small quantities of mineral matters (ash). Neradol D contains considerable amounts of soluble non-tannins, derived from salts of sulphonic and sulphuric acids, again offering a satisfactory explanation of the high ash. If, therefore, a mixture of Neradol D and a natural tanning extract was submitted to a quantitative analysis, the higher non-tannins and the high ash would indicate the presence of Neradol D, provided that wood pulp or a highly sulphited extract were not components of the mixture.

The chemical reactions taking place in the preparation of Neradol D may be expressed thus:-

OH OH OH OH
H ^ H___O_____H ^ H H ^ H__CH_2__H ^ H
| | || | | = | | | | + H_2O
| | CH_2 | | | | | |
H v CH_3 CH_3 v H v CH_3 CH_3 v H
HSO_3 HSO_3 HSO_3 HSO_3

1. Neradol D Reactions

1. The quantitative determination of phenols introduced by Bader, [Footnote: _Bull. soc. scient., Bucarexi_, 1899, 8, 51.] which consists in precipitating them as oxyazo compounds, has been modified by Appelius and Schmidt [FootNote: _Collegium_, 1914, 597.] for the purpose of detecting Neradol D:--To 50 c.c. of the tannin solution (analytical strength) 15 c.c. of diazo solution are added, the mixture filtered, if necessary, and the filtrate made alkaline with caustic soda; in the presence of Neradol D in sufficient quantity, a blood-red coloration results. If but little Neradol D be present, the procedure is altered as follows:--The tannin solution, to which the diazo solution has been added, is filtered, and the filtrate poured on a piece of filter paper which is then dried; a solution of caustic soda is spotted on the paper, when, if Neradol D be present, a red-edged spot will appear.

According to Tschirch and Edner, [Footnote: _Archiv. d. Pharm_., 1907, 150.] the diazo solution is prepared as follows:--5 gm._p_-nitraniline are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6 c.c. concentrated sulphuric acid added, the mixture shaken and a solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of water added, and the whole then filled up to 500 c.c. The solution should be stocked in the dark.

2. A less sensitive reaction for Neradol and wood pulp extract constitutes that of Appelius and Schmidt employing cinchonine, [Footnote: _Collegium_ 1914, 597.] while the presence of the substances in question yields characteristic precipitates.

3. Seel and Sander [Footnote: _Zeits. f. ang. Chem._, 1916, 333.] recommend the following method of detecting Neradol D:--

_(a) Oxyazo Reaction_.--About 5 c.c. of the tannin solution are rendered alkaline with caustic soda; after cooling with ice, about half the volume of alcohol is added. 3-4 drops of diazo solution are then added. Frequently, this results in the solution assuming a blue coloration. If not, the solution is acidified with hydrochloric acid, ether added, and the mixture well shaken. The water is now separated from the mixture, fresh water added, together with some caustic soda solution, when, if Neradol D be present, the salt of the colour acid formed dissolves in the water with a beautiful green or bluish-green colour. At the place of contact of the water and the ether a bluish-green ring appears.

The diazo solution is prepared by dissolving _p_-aminophenol or its hydrochloric in a little dilute hydrochloric acid, cooling in ice and carefully diazotising in the cold till a slight excess of nitrous acid is present. It is essential that this solution should be tested before use, and this is carried out by coupling it with an alkaline phenol solution; if a dark blue oxyazo colour is formed, the solution may be used. It must be kept cool by surrounding it with ice.

_(b) Indophenol Reaction_.--To 5 c.c. of the solution to be tested, a drop of a solution of dimethyl-_p_-phenylenediamine is added, the solution rendered alkaline with caustic soda and 1-2 drops of a 5 per cent. solution of potassium ferricyanide added. If Neradol D be present, a blue colour appears, either immediately or after some time. The reaction is rendered more sensitive if alcohol is carefully poured on the solution after it has been rendered alkaline, and potassium ferricyanide is then added. At the place of contact a blue layer is formed, which ultimately diffuses into the alcohol.

According to Lauffmann [Footnote: _Collegium_, 1917, 233.] the presence of natural tannins as well as that of wood pulp diminishes the sensitiveness of the reactions described above; [Footnote: _Zeits. f. ang. Chem._, 1916, 333.] this investigator recommends a modification of these reactions.

2. Electro-Chemical Behaviour of Neradol D

The author's investigations of the electro-osmosis of an aqueous solution of Neradol D [Footnote: _Collegium_, 1920, 597, 24.] proved that dicresylmethanedisulphonic acid exhibits anodic migration; hence this product possesses negative charge and acidic character. The impurities accompanying the synthetic tannin, _i.e._, salts, free sulphuric acid, and some phenols, migrated anodic and cathodic respectively, according to their charges. A Neradol D purified by electro-osmosis finally yielded a pure solution of dicresylmethanedisulphonic acid, which precipitated gelatine and exhibited pronounced tanning effects, but gave a greenish-black coloration with iron salts. This conclusively proves that the blue coloration given by Neradol D with iron salts is no characteristic feature of the _pure_ synthetic tannin, but is caused by the phenolic impurities accompanying the latter. Especially the first stage of the electro-osmosis produces a cathodic migration of the phenols, which may then be detected at a cathode by means of the iron and bromine reactions.

It is characteristic of a dicresylmethanedisulphonic acid purified by electro-osmosis that it does not precipitate aniline hydrochloride. It appears, therefore, that this reaction--which is characteristic of most synthetic tannins--is again caused by the presence of impurities.

3. The Influence of Salts and Acid Contents on the Tanning Effect of Neradol D

Chemical analysis of crude Neradol revealed a natural dicresylmethanedisulphonic acid (the tanning agent) contents of about 68 per cent, which agrees fairly well with the calculated amount. Like other "strong" and "weak" acids this sulphonic acid exercises a strongly swelling influence on pelt. Whereas the effect of acid present in solutions of Neradol D of medium concentration and its tanning effect both influence the pelt and are fairly well balanced, this is not the case as regards highly concentrated and very dilute solutions. If, for instance, a very dilute solution of crude Neradol (about 0.25° Bé.) is used, the tanning effect of this solution is exceedingly small and does not show itself till after several hours. The relatively high dissociation of the acids at this high degree of dilution causes an extremely rapid and strong swelling of the pelt, which has therefore absorbed its maximum amount of water (maximum swelling) before the tanning effect of the sulphonic acid comes into play and by fixing the surface of the pelt is enabled to prevent the excessive swelling effect of the acids.

The addition of neutral salts to the tan liquor diminishes the effect of the acids on pelt (dehydrates the pelt) and prevents "drawing" of the grain. If, for instance, common salt be added to a solution of crude Neradol, the original quantity of sulphonic acid present would remain constant, but the presence of salt would diminish the degree of dissociation and consequently the swelling. This effect is still more pronounced when the absolute amount of free sulphonic acid is diminished. Hence, if crude Neradol is treated with increasing amounts of caustic soda, a series of products containing increasing quantities of salt and decreasing concentrations of sulphonic acid is obtained.

The acidity of the Neradols may be determined by titration with N/10 caustic soda; this procedure hence establishes a means of determining the (unknown) acidities which may be expressed in terms of c.c. N/10 NaOH. The acidity of crude Neradol was found to be--

1 gm. = 50 c.c. N/10 NaOH

_i.e._, 1 gm. of crude Neradol requires 50 c.c. N/10 NaOH for complete neutralisation; the decrease in acidity causes a decrease in contents of tanning matters and the quantities of salts increase. The following table gives the figures obtained by differently neutralised neradols:--

Acidity. Tanning Matters. Na_2SO_4.

Per Cent. Per Cent.
1 gm. = 50 c.c. 68 ...
1 gm. = 40 c.c. 59 4
1 gm. = 30 c.c. 50 8
1 gm. = 20 c.c. 41 12
1 gm. = 10 c.c. 33 17
1 gm. = 5 c.c. 28 20
1 gm. = 0 c.c. 20 ...

Tanning experiments with these different neradols (employing solutions of 1° Bé. strength) demonstrated that neradols of acidity 50°, 40°, and 30° exerted strong swelling and gave comparatively hard leathers; neradols of acidity 20°, 10°, and 5° exert no swelling, yield quick tannage and soft leather. The swelling (hardening) effect of the acid and the dehydrating (softening) effect of the salts in this case, therefore, are well balanced, and this fact affords an explanation of the rapid change from hardening to softening effects exhibited by partly neutralised Neradol where less acid and a greater quantity of salts respectively are present.

It may finally be noted that the acidity of Neradol D, 1 gm. = 10 c.c. N/10 NaOH, has been found to be the most suitable one for practical purposes. The author has, however, successfully employed some neradols of considerably higher acidities. The acidity above mentioned is possessed by a Neradol D containing 17 per cent. ash and 30 per cent. sodium sulphonates and Glauber's salts crystals respectively. This large quantity of salts present on the one hand effects the rapid pickle and tanning effect exhibited by Neradol D, on the other hand it also effects the softness in the leather resulting from its use either alone or in admixture with natural tannins.

4. Phlobaphene Solubilising Action of Neradols

A special feature of Neradol D is its property of solubilising phlobaphenes, which may be ascribed to its contents of sulphonic acids or their salts. In order to demonstrate whether the sulphonic acids and their salts are capable of solubilising the insoluble or sparingly soluble anhydrides of the tannins (the phlobaphenes) before and after condensation, the following experiments were carried out:--

Crude Argentine solid quebracho extract was converted into a highly viscous liquid by treating it for several hours with water at 100° C., and the anhydrides rendered insoluble by diluting the liquid with a large volume of cold water. The precipitate formed, consisting of quebracho phlobaphenes, was separated from the liquid by decantation, and purified by washing it several times with water. Each 10 gm. of this moist paste were treated in the cold with (_a_) free phenolsulphonic acid; (_b_) sodium phenolsulphonate; (_c_) crude Neradol and (_d_) Neradol D, 20 c.c. of water at 45° C. added, and the mixture allowed to cool slowly; the following solutions resulted:--

(_a_) Opalescent solution, much deposit,
(_b_) Clear solution, no deposit.
(_c_) Nearly clear solution, very little deposit.
(_d_) Clear solution, no deposit.

This clearly proves that free and condensed phenolsulphonic acids as such are not capable of completely solubilising phlobaphenes, whereas the sodium salts of free and condensed phenolsulphonic acids possess this property. The salt contents of Neradol D, therefore, constitute an advantage in this respect, that not only may Neradol D be mixed with solutions of any natural tannin without insolubles being thereby deposited, but it may also be added in large quantities to a tannin solution with the result that the sparingly soluble and wholly insoluble constituents (phlobaphenes) are completely brought into solution.

The practical importance of the solubilising effect of Neradol D relating to solid Argentine quebracho extract is demonstrated in the following series of investigations carried out by the author:-- [Footnote: _Collegium_, 1913, 478; Austr. Pat., 68, 796.]

Solid Neradol Matters Tanning Abs. Increase Argentine D. Calc. of Mixture Increase per Quebracho Found. in Tanning 100 gms. Extract. Matters. Extract.

Gm. Gm. Per Cent. Per Cent. 100 0 66.0 66.0 ... ... 0 100 32.5 32.5 ... ... 90 10 62.7 64.7 2.0 2.2 80 20 56.1 58.7 2.6 3.3 60 40 52.6 56.9 4.3 7.1 50 50 49.3 55.2 5.9 11.8 30 70 42.6 47.3 4.7 15.6 20 80 39.2 42.3 3.1 15.5

The maximum solubilising effect is exhibited in the mixture of 70 parts of Neradol and 30 parts of quebracho, with an additional percentage of tanning matters in the mixture of 15.6 per cent.--a figure which is very nearly identical with that of the insolubles present in the original Argentine quebracho extract.

The phlobaphene-solubilising property of Neradol D is closely connected with the influence of the latter on the colour of leathers tanned with natural tannins. If, on the one hand, a pelt is tanned with natural (_i.e._, non-treated) quebracho extract, a rather light coloured leather results, the fleshy colour of which is characteristic of quebracho. The dark coloured phlobaphenes present, on account of their insolubility, will have no influence on the colour of the leather. If, now, the quebracho extract be treated with sulphite and bisulphite in the usual way, the phlobaphenes are solubilised, but the reducing effect of the bisulphite tends to brighten the colour of the otherwise dark coloured phlobaphenes as well as that of the soluble tannins, and a reddish-yellow coloured extract results, imparting its own colour to the pelt. When, on the other hand, the quebracho extract is solubilised by means of Neradol D, the phlobaphenes are brought into solution without reduction taking place, and a dark brownish-red extract results, which imparts a similar colour to the finished leather. This darkening effect of Neradol D is most conspicuous in the case of mangrove, maletto, and chestnut, but is absent in the case of algarobilla, dividivi, gambir, sumac, and valonea. The varying phlobaphene contents of the tannins easily afford an explanation of the different properties above alluded to: the mangrove phlobaphenes are dark coloured bodies, those of mimosa, maletto, and chestnut are of lighter colour, and the last-named tanning materials enumerated above are either devoid of phlobaphenes or possess them only as very light coloured bodies. Algarobilla, sumac, gambir, dividivi, and valonea, on the other hand, are associated with large amounts of sparingly soluble ellagic acid, known as "bloom" or "mud" which imparts a light colour to the finished leather, and conveniently covers the dark colour imparted to the leather by other tanning materials; for this reason the former are often used in the lay-aways or in the finishing processes.

Similar effects to those of Neradol D are exhibited by other salts of sulphonic acids, _e.g._, sodium benzylsulphanilate (Solvenol B.A.S.F., or solution salt ("Solutionsalz") Hoechst); the author prepared mixtures of such salts and untreated quebracho extract in order to determine their solubilising effects, and arrived at the following results:--

30 parts Solvenol plus 70 parts quebracho extract: clear solution,
no deposit.

25 parts Solvenol plus 25 parts quebracho extract: clear solution,
very little deposit

20 parts Solvenol plus 80 parts quebracho extract: nearly clear solution,
very little deposit.

15 parts Solvenol plus 85 parts quebracho extract: slightly opaque solution
some deposit.

Leathers tanned with these mixtures were more or less dark coloured according to the amounts used of solvenol and the consequent solubilisation of the phlobaphenes.

A similar effect, though of opposite nature from a tanning standpoint, is exhibited by sulphonates on certain colloidal dark coloured substances. A phenolsulphonic acid, which had been overheated during sulphonation and subsequently condensed (crude Neradol), imparted a conspicuous greyish-brown colour to the leather; samples of this crude product were then partly neutralised with varying amounts of alkali, and these samples (containing increasing quantities of salts) tested for tannin and colour effects. It was found that the more highly neutralised samples imparted a darker colour to the solutions, but these dark products did not deposit the dark impurities on the pelt. One may therefore assume that tannoid substances are colloidally suspended, and when converted into true solutions are incapable of being fixed in insoluble form by the pelt.

Just as, by adding Neradol D to a tanning extract, the phlobaphenes are 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.