Colorado College Tutt Library

Century Chest transcription 95

E.C. Woodward

Notes on Assaying

This sign is the Swastika an emblem of good luck dating from the Bronze Age

Colorado Springs, Colorado, Aug. 5 1901

To my friends of the 21st Century

As it may furnish some data to know the progress made between your time and this, I write these notes of the present state of assaying for gold, silver, & lead.

These metals are determined by fire assay though we know the fire assay of lead is inaccurate, yet as the ore is reduced by practically the same process it is the commercial assay.

Silver is assayed either by verification or crucible assay and gold almost invariably by crucible.

As the ore is sold by Av.Ton. and gold and silver by Troy oz. and we weigh our results in grammes the assay change is weighed by the Assay Ton, a compromise between these:

1. Ton. Avoirdupoise = 29166 Troy oz.
1. Assay Ton = 29.166 milligrammes

Therefore if we melt 1. A.T. (29166 milligrammes) and find 1 milligramme of gold the ore sums 1 oz. per Av. Ton.

For verification of silver we take 1/10 A.T. mix it with 1/2 Assay ton of test lead (five grams) and cover with an equal amount of lead.

For the crucible assay 1/2 A.T. is the general charge. I use a flux of the enclosed composition unless we know an ore carries enough silver about 10 m.g. of silver is added to each crucible that there may be enough silver present to part the button.

I fire the charge 1/2 hour, pour in an iron mould [?] pound off the day [?] and crupel [?].

On control assays we are expected to check the other assayer within .05 oz or $1.00 per ton.

Control assays are those on which ore is settled. The buyer crushes and mixes the whole lot to be punctured takes out 1/10 of this mixes and makes finer and continues the process until about 24 oz. is left. This is put through 100 mesh screen and divided into three parts. The sellers have one, the buyer a second and the third is sealed and put away for reference. The seller takes his sample to an assayer who determines its value the buyer does the same and if the two assays are within .05 oz per ton on medium grade ore (2 oz ($50 ore)) the two are averaged for the value and the buyer draws a check for the value of the ore. If the two assays do not agree closely the assayers repeat and if they still disagree the third sample is sent to another assayer called the Tromprit [?] who takes extra care, and his result settles the matter. For control assays I use four crucibles of 1/2 A.T. each, weigh each result separately combine in pairs of two and weigh, then weigh all four. The result in millegrammes divided by 2 is the value per ton.

My balance is made by Ainsworth of Denver, it has a five inch beam divided to tenths and each of these divisions into fine parts. I use 1 m.g. sides and the balance readily shows 1/2 of 1/10 v or 1/100 m.g.. I can weigh carefully one result in about a minute.

Enclosed are assay result of Cripple Creek one sold to the Colo. City works and a plan of the assay furnace I use. I burn bituminous coal and can push to furnace to about 2200 Fr.

My Balance for Analytical work is made by Smith & Thompson of Denver. It has a six inch beam will carry a load of 200 grammes on each pan and is sensitive to 1/10 m.g.

We have trouble with weights for weighing gold results as there is not standard make and sets from different makes vary up to .04 m.g.. If improvements in balance and process continue till your time as they have since I came to Colorado, 1883 you will not suffer from many things that trouble us.

I write this in pencil lest ink be as evanescent as our memories.

Eli Woodward

Lead Assay

10 grams. Ore in a flux of

10 Na2CO3
13 K2CO3
10 Borax
3 Flour

Fire 25 minutes at good red heat

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