On the left is the Deposit or Weighing-room, where all the gold and silver for coining is received and first weighed. The largest weight used in this room is five hundred ounces, the smallest, is the thousandth part of an ounce. The scales are wonderfully delicate, and are examined and adjusted on alternate days. On the right of this room is one of the twelve vaults in the building. Of solid masonry, several of them are iron-lined, with double doors of the same metal and most complicated and burglar-proof locks. [Illustration: AUTOMATIC WEIGHING SCALES.] It is estimated that about fifteen hundred million dollars worth of gold has been received and weighed in this room; probably nine-tenths of this amount was from California, since its discovery there in the year 1848. Previous to that time the supplies of gold came principally from Virginia, North Carolina, and Georgia. During the past ten years considerable quantities have been received from Nova Scotia, but most of the gold that reaches the Mint, at the present time, comes from California, Montana, Colorado, Idaho, Nevada, Arizona, Oregon, Dakota, Virginia, South Carolina, and New Mexico. Formerly the silver used by the Mint came principally from Mexico and South America, but since the discovery of the immense veins of that metal in the territories of the United States the supply is furnished from the great West. The copper used comes principally from the mines of Lake Superior, the finest from Minnesota. The nickel is chiefly from Lancaster County, Pa. THE DEPOSIT MELTING ROOM. After the metal has been carefully weighed in the presence of the depositor and the proper officials, it is locked in iron boxes and taken to the melting room, where it is opened by two men, each provided with a key to one of the separate locks. There are four furnaces in this room, and the first process of melting takes place here. The gold and silver, being mixed with borax and other fluxing material, is placed in pots, melted and placed in iron moulds, and when cooled is again taken to the deposit room in bars, where it is reweighed, and a small piece cut from each lot by the Assayer. From this the fineness of the whole is ascertained, the value calculated, and the depositor paid. The metal in its rough state is then transferred to the Melter and Refiner. OFFICE OF THE MELTER AND REFINER. Adjoining the Deposit Melting Room are the Melter and Refiner and assistants. This is the general business office of the head of this department, and is also used for weighing the necessary quantities of the metals used in alloying coin. THE PROCESS OF ASSAY.