This section is from the book "The Manufacture Of Liquors, Wines, And Cordials, Without The Aid Of Distillation", by Pierre Lacour. Also available from Amazon: Manufacture of Liquors, Wines, and Cordials, Without the Aid of Distillation.
Take of sweet almonds, sixteen ounces; bitter almonds, four ounces; water, three pints; refined sugar, six pounds. Having blanched the almonds or removed the husks by soaking them in warm water for a few moments, and rubbing them through the hands until the husk comes off; having blanched the almonds, rub them in a mortar to a very fine paste, adding during the trituration, three fluid ounces of water and a pound of sugar. Mix the paste thoroughly with the remainder of the water, and then strain the mass through a common coarse linen cloth, Add the remainder of the sugar to the strained liquor, and dissolve it by the application of a gentle heat. Having become perfectly cool, bottle it, which must be well stopped and kept in a cool place; half a pint of orange flower water greatly improves the above. This syrup will not keep long, as it is liable either to ferment or become rancid. This syrup is prepared in a cheap manner, for auctions, etc, by adding any convenient quantity of the mucilage of slippery elm bark. This is prepared by boiling ten ounces of the bark, in a gallon of water, for one hour; if allowed to cool when the mucilage is deposited, any given quantity of the syrup is increased in quantity by the addition of any desired quantity of the mucilage. Orgeat can be colored any desired color, but owing to its heavy consistency, its natural color is preferable. When it is to be colored, the water is first colored the desired color.