JELLY includes every translucent juice so far thickened as to coagulate when cold into a trembling mass; as the juices of acid or muci laginous fruits, currants, etc., which, by the addition of one part of sugar to two parts of juice, and, by boiling, have obtained a proper consistence.
1. Animal soft parts, such as the muscles, skin, cartilage or integuments of animals, when boiled in water, yield a solution which on cooling solidifies to a tremulous jelly. Seventy pounds of bones, when treated with one pound of water in the form of steam, at a pres sure of four pounds to the square inch and sim ultaneously digested in •five gallons of water, will yield about 20 gallons of a strong jelly.
Animal jelly seems to be nearly identical in composition with the tissues which yield it, so that we are unable to trace any chemical change, except, perhaps, the assimilation of water dur ing the process of its manufacture. The fol lowing analysis shows the average percentage of carbon, hydrogen and nitrogen in animal jelly: Carbon Hydrogen Nitrogen 49.0 7.0 19.4 50.0 6.5 17.5 2. Vegetable Jelly.— When the juice of fruits is heated with sugar, the liquid forms a stiff jelly on cooling. It appears from the re searches of Fremy and others that unripe fruits contain a compound of carbon, hydrogen and oxygen called pectose; as the fruit ripens, this substance is transformed into pectin, the change being brought about chiefly by the influence of a peculiar ferment called pectase, which is con tained in the fruits. As pectin is soluble in
water, the expressed juice of ripe fruits con tains a large quantity of this substance, which on heating to a temperature of about 105° F. is converted into one or more substances which have not as yet been completely studied, but which have the property of gelatinizing on cool ing. The principal of these substances are pec tosic and metapectic acids. This latter acid, when boiled along with another strong acid, whether mineral or organic, is decomposed, one of the products being pectin sugar, a substance which is closely allied to glucose, so that in all probability there is produced in the very proc ess of manufacturing jellies more or less of this sugar, which certainly is not cane-sugar, and which might, therefore, be by some re garded as an adulteration. The processes which, in the living plant, result in the trans formation of pectose into pectin may be imi tated on a small scale by heating the juice of unripe fruit with the pulp, which contains the ferment pectase, or with a dilute acid which induces the same change as this substance. Al kalis also produce a similar effect.