Boise’s Assay Office played an important role for the whole nation

The 1870 U.S. Assay Office is Boise’s only National Landmark building.
The 1870 U.S. Assay Office is Boise’s only National Landmark building. Provided by Arthur Hart

The United States Assay Office at 210 Main St. in Boise (1870-71) is one of only three National Landmark buildings in Idaho. To be considered a National Landmark, a building must be important in the history of the nation, not just in state or local history.

Idaho’s other National Landmark buildings are The Mission of the Sacred Heart to the Coeur d’Alene Indians near Cataldo (1850-53) and Experimental Breeder Reactor No. 1 near Arco (1951). The mission is Idaho’s oldest building, and EBR No. 1 was a landmark in the atomic age when the power of the atom, so horrendous in war, was turned to the peacetime generation of electricity.

Boise’s Assay Office was built by the federal government to fill the need for a reliable way of testing the value of the gold being mined in large quantities in all sections of the Idaho Territory. Gold is nearly always found mixed with other metals of lesser value, silver being the most common. The purity of gold can be determined by exposing it to nitric acid, which has no effect on the real thing but breaks down other metals. Purity is expressed as 10, 14, 18 or 24 carats, with 24 carat being too soft for some uses, including most jewelry. If a nugget is pounded with a hammer, it will flatten until it is thinner than paper but will not shatter. If it shatters, it is probably pyrite or some other gold lookalike.

In the 1860s, before there was a federal assayer in Idaho, assaying was done by a few individuals, some small companies and most banks. Between 1861 and 1866, Idaho Territory produced about $52 million in gold ($728 million in today’s dollars). As the sheer volume of gold to be tested increased, the nearest facility for large-scale assaying was the U.S. Mint in San Francisco, and sending gold there was costly and time-consuming, making the need for an office here imperative.

In January 1867, the Tri-weekly Statesman reported that A.H. Robie and Alexander Rossi had decided to establish a Boise Assay Office. “Mr. Rossi is an able and careful assayer, possessing the advantage of long experience in the business and a reputation second to none. His gold bars are as current as gold coin wherever they are known.” A month later the Statesman said, “There is every reason why we should rejoice and be glad that we can get an assay office.”

In 1869, Congress appropriated $75,000 to build a U.S. Assay Office in Boise, and it was Rossi who donated the city block bounded by Main, Idaho, First and Second streets upon which to build it. Ground was broken in July 1870, and construction began on a building designed under the direction of Alfred B. Mullett, supervising architect of the U.S. Treasury. Mullett, who was born in England, was 36 at the time and had served in the Union Army during the U.S. Civil War. During his eight years as supervising architect, he had compiled an impressive list of federal buildings, including the Carson City, Nev., Mint, the San Francisco Mint and the Pioneer Courthouse in Portland. In 1890, in financial trouble and ill health, Mullett committed suicide. He was 56 years old.

John R. McBride, who had served in the Oregon Senate and as a member of the U.S. House of Representatives from Oregon, was appointed chief justice of Idaho Territory by President Abraham Lincoln in 1864. In 1869, President Ulysses S. Grant named him superintendent of the U.S. Assay Office in Boise. The Statesman reported regularly on the progress of construction at the site. On April 20, 1871: “Work on the Assay Office is being driven ahead as fast as circumstances will permit. A force of 15 men is employed. Judge McBride estimates that the building will be completed and ready for the reception of the assaying works in about six weeks.”

Next week: The history of this notable landmark from 1871 until today.

Arthur Hart writes this column on Idaho history for the Idaho Statesman each Sunday. Email histnart@gmail.com.