This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
Made first by Prevost about 1735, the same who took in partnership Phillippe, who afterwards became celebrated for his restaurant in Paris. It is refined glue; may be obtained by boiling down calves' feet, head, ears or skin until they are dissolved, straining the liquor and then drying it on shallow dishes. The transparency of some kinds is due to clarifying processes. The whitish kind in sheets is porous through being churned while cooling, which makes it easier to dry, and is an advantage in cooking as:t floats in the liquid and cannot burn on the bottom as the transparent kinds do. Gelatine is one of the expensive articles of hotel provision. The dearest is not necessarily the best. The jellies to be made have to be clarified by the cooks and one kind of gelatine is as good as another provided it is without flavor. If kept in a drug store gelatine will often acquire flavors from neighboring substances that render it quite worthless. The quantity required is 1 1/2 ounces for 1 qt. of jelly, or 1 oz. for 1 qt. of milk or cream for blanc mange, but more in warm weather than in cold.
Gelatine jelly can be made of double strength, then dried down to the consistency of gum drop candy, in small pieces or shreds, and kept, and when wanted to make jelly can be dissolved in the right measure of hot water, and will be jelly as soon as it can be made cold enough to set. (See Fellies, Aspic, Cremes).