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:--