Polynemus plebius, Broussonet, L., C. and V.
P. lineatus, Lacepede. I P. Commersonii, Shame, I'. niloticus, Shaw. Bynni, Bruce.
Pole kala, . . . TAM.
Length, 4 feet. It inhabits the Coromandel coast, Otaheite, Isle of France, and Isle of Tanna. Its value as a fish yielding isinglass unknown.
Pristipoma hasta and Pristipoma olivaeeurn, of the family Percidm, are common round the coasts of India, and their air-bladders are largely exported to China.
Umbrina Russelli, C. and V., Richardson.
Ikan gulama, . . MALAY. I Qualar katchelee, . TAM.
Total length, 6 inches to 1 foot ? Inhabits seas of Penang, Malay Peninsula, Singapore, Vizag,a patarn, Indian and China seas. Its isinglass is considered of good quality.—Russell.
The Indian isinglass is not prepared with any thing like sufficient care to obtain a place in the markets of Europe. Good isinglass cannot be made without considerable attention being paid during the processes of washing, beating, scrap ing, and drying, all of which have a very im portant influence on the goodness of the finished isinglass. The imperfect solubility of some, and more especially of the thick pieces, is, occasioned by the presence of a considerable quantity of albumen, or insoluble membranous matter having most of the properties of albumen, which is not only itself insoluble, but in addition renders much of the gelatine with which it is associated like wise insoluble. It is more than probable that the greater part of this albuminous substance might be readily removed by sufficiently scraping the isinglass during its preparation. Attention should also be directed to the process of drying,tas, if not properly dried, it might possibly undergo a slight change or decomposition, and become par tially converted into a more insoluble form of gelatine. A more important. objection is the smell, which, however, may likewise, to somo extent, be traced to the preparation. Much greater ,care is bestowed on the preparation in Russia than in India. Boiling with fresh-made charcoal would probably have the effect of de priving inferior isinglass of some of the smell and colouring matter when required for the purposes of a jelly. • Isinglass cut into threads is unsuitable for the English commerce, notwithstanding that isinglass for retail is cut into fine threads, as more convenient for general use, and for making jellies and soups, in consequence of the extensive surface which is exposed rendering it more easily and quickly soluble. But there is a great pre
judice in the wholesale market to buying things in a cut or powdered state, in consequence of the innumerable methods adopted for falsifying and adulterating almost every drug. Machinery is used in London for cutting the isinglass into threads of any degree of fineness ; and as it is impracticable at present to rival this in India, besides having to contend against prejudice if sent in this state, it is preferable, and will be cheaper, to prepare the article and send it as sheet isinglass, that is, the form of the slit sounds them selves, or their purest membrane, washed, cleaned, and dried in the best manner. The Indian isin glass, as at present prepared, is complained of as too thick if intended to come into competition with the superior varieties of Russian isinglass. Some of it may, without difficulty, be rendered thinner, for even in the dried state, layers of membrane which display a fibrous structure may be stripped off, and which no doubt contain the greater portion of the insoluble albumen. It might also be made thinner by beating, or pressing between iron rollers or marble slabs, as is done with American and some kinds of Brazilian isin glass. The extra labour which this would require might be profitably saved, by not tearing it into fibres, in which state it is disapproved of in the market ; but it might still be cut or rasped into a state fit for domestic use. The refuse should be turned to account ; the soluble parts of the sounds separated from the insoluble, and poured out into thin plates, and dried on nets, as is done with some of the gelatine of commerce. In order to ascertain the value of the article (merely stripped of all impurities calculated to injure its quality, without any regard to appearance), a • considerable quantity was sent to England by Dr. M'Clelland. From the account received of the sale, it appears that this isinglass realized only ls. 7d. per pound, which was considerably under its prime cost.—Dr. Boyle on Isinglass, p.11; Cantor, Malayan Fishes in J. B. As. Soc. ; Mason's Thnasserinz ; Dr. Day on the Air-bladder of Fishes; Jerdon, Fishes.