1855.] 



THE MDJTS OP THE UNFfED STATES. 



129 



tails of their operations. As the gold is brought to the Mint 

 in various quantities anil in a crude state, it passes necessarily 

 through the department of the refiner before it reaches that of 

 the chief coiner ; I therefore give the actual details of the re- 

 fining operations upon sundry deposits of gold, amounting in 

 the aggregate to $2,000,000. 



The deposits are immediately weighed and a certificate of 

 their gross weight issued. The fires having been lighted in 

 the five furnaces of the deposit melting-room at four or five 

 o'clock, A.M., all the deposits, amounting perhaps to seventy 

 or eighty, are melted before noon ; assay slips are then taken 

 off and the assays finished * the next morning, after which 

 their values are calculated by the weight after melting, care 

 being taken to include all the grains that can be procured from 

 the flux, pots, &B., by grinding them up under a pair of small 

 chasers, sifting, and washing. There is a clerk and his assis- 

 tant and one hand wholly engaged in performing all the weigh- 

 ings for the treasurer, such as weighing deposits before and 

 after melting, ingots for coinage, fine bars, and the clippings 

 after cutting out the planohets. There are five men in the 

 deposit melting-room, two of whom attend to two furnaces 

 each at the same time, one to one furnace and washing grains, 

 and the remaining two are labouring a.ssistants. The whole 

 deposit of 82,000,000 is melted in three or four days in the 

 deposit-room and assayed by from the third to the seventh 

 day. 



As soon as the first deposits are assayed, say on the third day 

 (if expedition is neoessarj'), or always on the fourth, they are 

 granulated in the proportion of one part of gold to two parts of 

 silver. The pots contains 50 lb. of gold and 100 lb. of silver, 

 equal to 1800 oz., and each melt requires about an hour. 

 With four furnaces (attended by four melters and two aids), 

 there are ordinarily made thirty-two melts per day, but when 

 hurried forty-eight melts can be made, making from one-third 

 of a million to one-half of a million dollars per daj. Two days' 

 work, or about 8(350,000 worth of gold, equal in weight to one 

 ton (avoirdupois' weight), are granulated for a single setting 

 with acid. The granulated metal is charged into large pots, 

 together with pure nitric acid of 39° Beaunie, between the 

 hours of seven and nine A.M. on the sixth day, and steamed 

 for five hours. The pots made in Germany, are 2 feet in 

 diameter by 2 feet m depth, set in plain wooden vats, lined 

 with o-sixteenth inch sheet-lead ; a single coil of copper pipe 

 passing around the bottom of the vat blows the steam directly 

 into the water in which the pots are set to about half their 

 depth. 



The vats are arranged in a small house in the middle of the 

 room with a large flue connecting with the chimney-stack, so 

 that when in action the odour of nitrous fumes is scarcely 

 perceptible in the building. The 82,000,000 require about sixty 

 such pots ; they are stirred about once each hour, say altogether 

 five times with simple wooden paddles; the next day (seventh), 

 the acid solution of nitrate of silver is drawn off by a gold- 

 syphon into wooden buckets, and transferred to the large vat, 

 in which it is precipitated by salt (chloride of sodium), and 

 fresh acid added to the metals, now containing very little silver. 

 Steaming for five hours on the seventh day completes the re- 

 fining of 8650,000. Early on the eighth one pot is drawn off, 

 washed with a little warm water, and the gold-powder transfer- 

 red to a filter. Fresh granulations are put into this empty 



* The mode of assaying is according to the " wet process" of Gay 

 Lussac. This is ton well known to need description here. 



pot, and the acid of the adjoining pot baled over upon them, 

 and thus through the series, the whole being re-charged in 

 from two to two and a-half hours. After steaming for five 

 hours, the acid which contained but little silver from the pre- 

 ceding day becomes a nearly saturated solution of nitrate of 

 silver. By this arrangement 4 J lb. of nitric acid are consumed 

 altogether for each pound of gold refined, and the latter is 

 brought up to 990 at 993 m. fine, — rarely below 990. Thus 

 every two days, 13,000 lb. of nitric acid are used. In the 

 course of the last year 1,000,000 lb. of pure nitric acid, at 

 seven cents per pound, equal to 870,000, were consumed. 



The gold is washed with hot water on the filter during the 

 eighth day, and until it is sweet (say by 7 P.M). The filter 

 consists of two layers of tolerably stout coarse muslin, with 

 thick paper between, in a tub with a false bottom, 2^ feet in 

 diameter and 2} feet deep, and mounted on wheels. One of 

 the men remains, after washing hours, until, 7 p.m., when the 

 watchman of the parting-room continues washing the gold and 

 silver until sweet, i.e., until the wa.sh-water ceases to colour 

 blue litmus paper. Early on the ninth day the wet gold is 

 pressed with a powerful hydraulic press, and the cakes 

 then thoroughly dried on an iron pan, at a low red heat. This 

 process saves wastage in the melting-pot, since there is no 

 water remaining in tli« pressed metal to carry off gold in its 

 steam. The same day (ninth) the gold is usually melted with 

 a less proportion of copper than is requisite to make standard 

 metal, and cast into bars, which are assaj'ed by noon on the 

 tenth. They are then melted with the proper quantity of cop- 

 per, partly on the same day, partly early on the eleventh, and 

 assayed and delivered to the coiner the same day. On the 

 fourteenth they are ready for delivery to the treasurer as coins. 



The silver solution drawn off from the pots is precipitated in 

 a large wooden vat of 10 feet diameter by 5 feet deep, and 

 the chloride of silver immediately run out into large filters [6 

 X 3 XW] where it is washed sweet. The filter is covered 

 with coarse muslin, and the first turbid water thrown back ; the 

 filter, which is on wheels, is then run over to the reducing vats, 

 and the chloride shovelled into them. There are four such 

 vats [7X4X2] made of wood and lined with lead, 1 inch 

 thick in the bottom. A large excess of granulated zinc is 

 thrown on the moist chloride in the vats, without the addition 

 of acid ; the reduction is very violent, and when it slackens, 

 oil of vitriol is added to remove the excess of zinc. The whole 

 reduction occupies a few hours, and after a night's repose the 

 solution of mixed sulphate and chloride of zinc is run off into 

 the sewer. 



About 2 tons of zinc per 81,000,000 of gold are employed ; 

 the silver, however, in this amount, saj- 10 per cent, by 

 weight, should only take, by equivalents, about 2400 lb., so 

 that nearly two equivalents of zinc for 1 equivalent of silver 

 are used. This is found to be advantageous, as both time and 

 space are greatly enconomised by this excess. 



The day after the reduction the reduced silver is washed, 

 and the second day it is pressed and dried by heat, the same 

 hydraulic press as for gold being used, but with different 

 drying-pans. The same silver is used again for making fresh 

 granulations, but as it accumulates from the Californian gold, 

 10,000 or 20,000 are now and then made into coin, great care 

 being taking in this case to aviod getting gold in it when 

 drawing off the silver solution, and in the press. 



Such are the actual working details in refining a specified 

 amount (82,000,000) of gold, the first-third of which is dc- 



