This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Liebig's directions: Take the best kind of coffee, grind it, moisten a pound with a few ounces of cold water and pack in percolator; saturate with cold water and pour on enough to leave a stratum above the coffee. Macerate for twelve hours and close the percolator tightly. Then proceed to percolate. After all the liquid has run off, close the orifice again, pour on some more cold water, macerate again for two hours, percolate, and repeat this operation until the water appears no longer colored. A large quantity of extract may thus be prepared.
Another method of preparing plain coffee extract is to pour one pint of boiling water on one pound of best ground coffee: Let stand one hour, then transfer to a percolator, and proceed to percolate. Add sufficient water until sixteen fluid ounces of extract are obtained. To this add one ounce of alcohol to preserve it. If intended to keep a long time, four ounces of alcohol should be added. The extract should be kept well stopped.
One ounce of the extract to a quart of syrup will be sufficient on the dispensing counter; or put a small quantity of the extract in the cup, add the sugar and cream if desired, and draw the hot soda water on it.
An ordinary extract of coffee may be prepared by boiling the residue of the other extracts with water, cooling the liquid and filtering. An addition of one ounce of alcohol to each sixteen fluid ounces of such extract is also recommended.