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Essential Fire Assay Terms

13-Mar-17

TContext07_Spitting.doc

as used in Textbooks

"Spit" - "Spitting"

 at beginning of cupellation

Author

Context

Bugbee

Carbon is an undesirable constituent of cupels as it reacts with the lead oxide formed giving off CO and CO2 which may cause a loss of the molten alloy due to spitting. (p. 90)

Fulton

The presence of CaO3 is very undesirable in bone-ash for cupels, as it begins to give off CO2 at 800º C, about the temperature of the beginning of cupellation, causing a serious spitting of the lead button, which entails a loss of the precious metals. (p. 77)

Fulton

If the buttons were placed into the cold cupel, the lead would melt before all the remaining moisture is expelled, which would then pass up violently through the molten lead, causing what is termed "spitting," i.e., the projection of small lead particles, carrying gold and silver from the cupel.

Some cupels, made from bone-ash containing CaCO3, will commence to spit after the cupellation has proceeded for some time and the temperature has risen to above 800º C.

This can be stopped by pulling the cupel to the cooler (front) part of the muffle, although the cupellation, after spitting, is to be considered unreliable.

When a piece of wood or coal is placed in the muffle to "open up" lead buttons, the cupels absorb gases at times, which later on, when the temperature rises, are again expelled, with a spitting of the lead. (p. 80)

Shepard

The presence of organic matter and of carbonates, nitrates, and other salts that decompose at cupellation temperature (850 to 900°C) or lower is undesirable, as the evolution of gases during cupellation causes loss by "spitting" of the lead. (p. 49)

Shepard

Whatever free moisture may be present in an air-dried cupel is expelled when the cupels are preheated in the muffle just before using, a practice which is necessary in all cases in order to remove combined water, CO2, and other volatile matter that would cause spitting and to avoid delayed opening of the buttons if placed in cold cupels.(p. 54)

Shepard

Before cupellation the set of cupels should be charged into the furnace and heated at 850 to 900°C for 10 min., with the draft slightly open to provide an oxidizing atmosphere. This will drive off free and combined water,
organic matter, carbon dioxide, and other volatile constituents that would otherwise rise through the lead during
cupellation and cause the ejection of particles of lead.

This phenomenon is known as "spitting" and is a source of loss to the assay in question, as well as the cause of salting other samples into which the globules of lead may fall. (p. 56)

Shepard

Ores that decrepitate violently are troublesome in scorification because of "spitting," which is the violent projection of small particles of lead from the scorifier.

... Place the scorifier into a muffle at 500 to 600°C, close the door and muffle draft, and heat for 2 or 3 min. until the lead is melted and danger of decrepitation or spitting is past. (p. 166)

Shepard

The bundle of lead foil containing the residue is frequently cupelled directly as a lead button from an ore fusion. Spitting, that is, the ejection of small droplets of lead into the air, is likely to take place soon after cupellation starts. This is caused by the action of the salts in the residue. Loss due to spitting is not so serious as one might expect; nevertheless, it should be avoided when high accuracy is desired. Spitting can be avoided by a brief preliminary scorification. (p. 196)

 

 

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spitting

Herausspritzen /
Spratzen

spatten

éclabousser

spruzzare

salpicar

отхаркивание

 

 

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Bibliography:

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 free download from

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REFERENCE BOOKS
"A Textbook on Fire Assay"                                                                Edward E. Bugbee
"Fire Assaying"                                            Orson C. Shepard & Waldemar F. Dietrich
"A Manual on Fire Assaying"                                                       Charles Herman Fulton
"The Sampling and Assay of the Precious Metals"                            Ernest Alfred Smith
"Metallurgy of Gold"                                                                                 Thomas K. Rose
"The Precious Metals
: comprising Gold, Silver and Platinum"               Thomas K. Rose
"A Text Book of Assaying"                                                   C. Beringer & J. J. Beringer


Bugbee
Shepard
Fulton
Smith
Rose1
Rose2
Beringer

 

 

Context: ►Assay Ton  ►Blank  ►Steps   ►Feathers  ►Matte/Speiss  ►Colours  ►Spitting  ►Sprout  ►Surcharge  ►Inquart  Hallmark  ►Cupels

Terms: ►Cupellation  ►Fire Assay  ►Reagents  ►Other Methods  ►Metals Sheets: ►Cupels  ►Crucibles  Index: ►Programme