Rhubarb Jelly (Cold)

From 1922:

One pound rhubarb, 6 oz. sugar, 1 gill water, gelatine, few drops carmine, custard sauce. Wipe rhubarb, but do not take off the skin; put into a lined saucepan with the sugar and water and cook slowly until reduced to a pulp. Rub through a hair sieve. Measure the liquid and to each half-pint allow ½ oz. of gelatine. Put into a saucepan together and stir over the fire until the gelatine has melted. Strain into a basin, add a little carmine, cool slightly, then pour into a wetted mould. Turn out and serve with custard sauce or cream. Time, one hour. Sufficient for 3 or 4 persons.