The finely-cut purified isinglass, which is now in general use, requires no clarifying except for clear jellies: for all other dishes it is sufficient to dissolve, skim, and pass it through a muslin strainer. When two ounces are required for a dish, put two and a half into a delicately clean pan, and pour on it a pint of spring water which has been gradually mixed with a teaspoonful of beaten white of egg; stir these thoroughly together, and let them heat slowly by the side of a gentle fire, but do not allow the isinglass to stick to the pan. When the scum is well risen, which it will be after two or three minutes’ simmering, clear it off, and continue the skimming until no more appears; then, should the quantity of liquid be more than is needed, reduce it by quick boiling to the proper point, strain it through a thin muslin, and set it by for use: it will be perfectly transparent, and may be mixed lukewarm with the clear and ready sweetened juice of various fruits, or used with the necessary proportion of syrup, for jellies flavoured with choice liqueurs. As the clarifying reduces the strength of the isinglass—or rather as a portion of it is taken up by the white of egg—an additional quarter to each ounce must be allowed for this: if the scum be laid to drain on the back of a fine sieve which has been wetted with hot water, a little very strong jelly will drip from it.
Obs.—At many Italian warehouses a preparation is now sold under the name of isinglass, which appears to us to be highly purified gelatine of some other kind. It is converted without trouble into a very transparent jelly, is free from flavour, and is less expensive than the genuine Russian isinglass; but when taken for any length of time as a restorative, its different nature becomes perceptible. It answers well for the table occasionally; but it is not suited to invalids.