Below are excellent research sources for the Friedensville Mines:

The National Canal Museum in Easton PA holds research documents and photographs related to the 1998-2000 study of the Friedensville area which resulted in the creation of the Ueberroth Zinc Mine Historic District and the seminal article in Volume XX of Canal History and Technology Proceedings by Nadine Miller Peterson and Dan Zagorski titled Zinc Mining in the Saucon Valley Region of Pennsylvania 1846-1986.

Lafayette College holds the best contemporary description of The President Engine including detailed drawings of the engine and pitwork which we believe were produced from original drawings. This document is a 1874 student thesis by engineering graduate Samuel Miller Riley entitled Thesis on the Steam Engine at the Lehigh Zinc Co's Mines Bethlehem (call number 0 1874 R573t).  

Lehigh County Historical Society has an excellent collection of historical records, journals and historical sketches related to the various communities within Lehigh County. 
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Lehigh University Special Collections holds a number of student thesis documents related to the 19th century mine and zinc production plant operations. Of particular interest in the Lehigh Collection is the records and photographs acquired from the Stabler Land Company which relate to the New Jersey Zinc Company Friedensville operations including mine maps, photographs and business correspondence. Some of the mine maps date to the 1850s and some of the business correspondence is associated with the 1880s mine operations prior to New Jersey Zinc's 1899 acquisition of the property.
The Moravian Archives is primarily focused on records related to the Moravian Church and community which founded Bethlehem in middle years of the 18th century and  "owned" the town until the 1840s. However, they also have some business records. Of great interest to us is the records they hold on the Lehigh Zinc Company which operated the mines from the 1850s until the 1880s. Included with these records are commercial documents related to property purchases, leases and various capital investments.  Among the records held are the commercial contract and specifications of The President Engine.