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.