30 PAINTING MATERIALS
Eydrolyzed Oils are oils or fats (see Oils and Fats) which have been split up
by the action of water under suitable conditions, glycerine and fatty acids being
formed in the process. t
Isinglass is a very pure fish gelatin (see also Gelatin and Fish Glue). It is
yielded by the sounds (swim bladders) of a limited number of fish, chiefly the
sturgeon, which, for centuries, has been the main source of the celebrated Russian
isinglass. North American isinglass comes mainly from the hake, but some is
obtained from the cod. It is nearly pure collagen. Alexander says (p. 221) that,
when soaked in cold water, it swells greatly without losing its organized, fibrous,
thread-like structure, but that boiling converts it into gelatin which, probably
because of the ease of its formation, yields a very strong jelly. It was formerly
used as an adhesive much more generally than it is at present. Thin, transparent
sheets of the mineral, mica, are often wrongly called ' isinglass.'
Japan Wax is prepared from the berries of various species of the sumach tree
(Rhus) which is cultivated in Japan and China for the lacquer it yields. The wax
is a by-product. The berries yield 15 to 25 per cent of wax which occurs on them
as a greenish coating. They are gathered and stored until * ripe,' and are then
crushed and the kernels are separated. The remaining crude wax is pressed in
wedge presses and is purified by remelting and sun-bleaching, the wax being kept
moist during the process. It is pale yellow or light brown in color with a pro-
nounced and characteristic odor. It acquires a white, powdery surface. Its melting
point varies from 48° to 55° C, that usually found being 53°; the wax solidifies
again at about 41°, and, when recently solidified, melts at 42° and only slowly
regains its original melting point. Its iodine value is low; Fryer and Weston (p.
156) give the average value of 6. It is readily soluble in benzene and petroleum
ether, and is sparingly soluble in cold ether; it is insoluble in cold alcohol, but
dissolves on warming and separates again on cooling. It is of hard and brittle
consistency with a conchoidal fracture. Physically, it resembles bleached beeswax.
Since it is similar to the waxes in physical properties, it is called a wax, and some
writers classify it with them. From a chemical standpoint, however, the term
£ wax * is, of course, a misnomer for it, as it consists largely of palmitin and free
palmitic acid together with a small proportion (less than I per cent) of dibasic
acids (e.g., japanic acid, €2^4262), and probably some soluble acids. (See also
Ofls and Fats.)
Kauri (see also Copal). The tree which produces this resin is a conifer, AgatUs
australis, growing to an immense height and age on the north island of New
Zealand. It is easily * run * and combined with oil, and the better grades make a
very good varnish for industrial purposes. It is believed by some to be inferior in
hardness and durability to Sierra Leone or Zanzibar copal varnishes. On the other
hand, certain investigations on 'blooming' tend to show that varnishes cor-
rectly made from Kauri do not bloom in the most humid atmosphere*