PDA

View Full Version : Using Specific Gravity To ID Mystery Alloy



Linstrum
07-29-2007, 12:37 AM
Yesterday I was down at the industrial scrap recycling yard that has become my own little private gold mine. I found a newly arrived “gold deposit” that looked very much like tin metal. It was bright shiny new stuff that was in the form of easily bent 1/2-inch wide strips cut from thin sheets. Besides being easily bent, it was also light silver or aluminum-colored like tin is, too hard to scratch with my fingernail but still soft enough to be scratched with a penny just like tin. When I bent it, though, it did not squeak, crackle, or groan like tin does, which is the best way to identify tin when pure. Zinc will also make a crunching sound when bent, but the sound as well as the appearances of the two metals are quite different, zinc making a noise more like a pecan shell cracking than a squeak when bent as well as being a darker bluish colored metal with the typical gray color reminiscent of galvanized steel since zinc is what is used for galvanizing. However, just because some light silvery colored metal does not squeak and squeal when bent is not proof positive that the stuff in question does not contain a high concentration of tin metal since a small amount of alloying metal such as copper, silver, lead, antimony, bismuth, phosphorus, arsenic, etc, will prevent the phenomenon referred to as “tin cry”. The only way to tell for sure if an alloy has tin in it is to do a chemical test, which is actually not that difficult for tin, but the reagents needed are unfortunately no longer available without going to a chemical supply house, and those businesses will not sell to a stranger walking in from the street. But there is one test that will work in this particular case that is real easy and anyone who reloads or casts boolits already has all the right stuff to do it with just sitting there ready to go!

In this case, the only other thing my mystery metal could be is lead since it superficially resembles tin rather closely except for being softer. Freshly cut lead is very nearly the same silvery color as tin and the two can only be told apart after a few days when the lead begins to darken from the formation of lead rust, which is a dull dark gray, and tin does not rust. If alloyed to make solder or Babbitt with tin or any of the metals listed in the example above for tin “cry”, though, the color match is impossible to tell apart even after a few days since the alloying metals prevent the lead from rusting and keep it bright. The only means left to tell them apart very quickly at this point is to find their densities, or specific gravities, since lead is a substantially denser element compared to tin. Lead is 11.34 times as dense as water and tin is 7.265 times as dense.
To find the density of a sample of metal it is simply weighed while under water and then this weight is compared to its weight out of water. Theoretically the weight should be checked in a vacuum since air also supports and buoys-up all objects as well, but its buoying properties are tiny compared to water and for our purposes for extremely dense materials like metals it can be conveniently ignored. I tied one end of a six-inch length of fine sewing thread onto my piece of mystery metal and the other end onto the pan mount pivot of my 509.9-grain capacity Hornady-Pacific powder scale and weighed the piece with it dangling down below the top of my workbench. After weighing it I got a glass of water and carefully lifted the glass up underneath the piece of metal until I could see through the glass that it was totally submerged. I got a plastic drink straw and teased the air bubbles loose that were hanging onto the thread and then weighed the piece under water. I weighed it three times and the three wet weights all agreed, so I was done. All that was left to do was the math part, which is straightforward. The dry weight was 167.2 grains and the wet weight was 151.5 grains. Subtracting the two weights left 15.7 grains, which is the weight of water equivalent to the volume of the piece of metal. We want to find how many times more the weight of the metal is than the weight of its volume of water, so dividing the dry weight by the difference of the weights gives this number. The specific gravity of the piece is 167.2 divided by 15.7, which gives the number 10.64968. Rounding off that number to a legitimate value gives us a specific gravity of 10.65. Since it is a whole bunch more than 7.265 but pretty close to 11.34, it is a good educated guess that the mystery metal is mostly lead with a smidgen of something in it to make it harder than my fingernail, probably antimony, and judging from its shape and where I found it, its use was as tare weights for balancing some kind of aerospace devices. Since I get wheel weights free but this stuff was selling for $0.50 per pound, I left it.

trooperdan
07-29-2007, 10:56 AM
I've done this before with the same aim in mind but I couldn't have explaind it so well! Good Job!

fourarmed
08-01-2007, 02:59 PM
I have been trying to come up with an accurate method of estimating alloy content from specific gravity or density. (Density in grams/cc is numerically equal to specific gravity, which is what Linstrum measured.) The catch is that when you alloy two metals, you can obviously assume that the masses add, but I don't think you can say the same thing about volume. I know if you mix water and ethanol, the volume of the mixture is about 10% less than the sum of the individual volumes.

WineMan
08-01-2007, 03:45 PM
The Discovery of Specific Gravity

The discovery of specific gravity makes for an interesting story. Sometime around 250 B.C., the Greek mathematician Archimedes was given the task of determining whether a craftsman had defrauded King Heiro II of Syracuse. The king had provided a metal smith with gold to make a crown. The king suspected that the metal smith had added less valuable silver to crown and kept some of the gold for himself. The crown weighed the same as other crowns but due to its intricate designs it was impossible to measure the exact volume of the crown so its density could be determined. The king challenged Archimedes to determine if the crown was pure gold. Archimedes had no immediate answer and pondered this question for sometime.

One day while entering a bath, he noticed that water spilled over the sides of the pool, and realized that the amount of water that spilled out was equal in volume to the space that his body occupied. He realized that a given mass of silver would occupy more space than an equivalent mass of gold. Archimedes first weighed the crown and weighed out an equal mass of pure gold. Then he placed the crown in a full container of water and the pure gold in a container of water. He found that more water spilled over the sides of the tub when the craftsman’s crown was submerged. It turned out that the craftsman had been defrauding the King! Legend has it that Archimedes was so excited about his discovery that he ran naked through the streets of Sicily shouting Eureka! Eureka! (Which is Greek for “I have found it!”).

From http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Physical_Chemical/SpecificGravity.htm

garandsrus
08-01-2007, 04:17 PM
I have attached a chart that I downloaded a while ago that has a chart of various alloys and their specific gravity. I have the full article if anyone is interested. I think this originally came from the Cast Bullet Organization.


The chart shows that the sample was somewhere between 15% antimony and no tin and 12% tin with no antimony. You look for the specific gravity in each column/row and then read the % of both tin and antimony that makes up this specific gravity. Unfortunately, the chart can't tell you which of the dozen or so mixes you have, but at least you have a range of possible values.

Either one is probably worth 50 cents per pound!

John

Linstrum
08-03-2007, 02:16 PM
Hi, guys, thanks for the input! I will start a new thread and post the formula used by metallurgists for determining the specific gravities alloys where the percentages of the metals are known.

leftiye
08-03-2007, 11:15 PM
Linstrum, Maybe we could combine that with this thread and maybe 45 NUT would think it was worth stickying.?!

Linstrum
08-04-2007, 12:53 AM
Hi, leftiye, that is a good idea and I'll get 45Nut's attention.

The problem is that the second part of this is really long and it will get lost down here at the bottom so I will go ahead and post it as a new thread until the two can be posted back-to-back so they can be made into one sticky.

If I try to add it onto my original by using the "edit" feature it will dump it because of being too long for the program to handle. I've run across that problem before with real long threads I tried to post.

45nut
08-04-2007, 12:57 AM
I'm watchin',,and can transfer it to the classics and stickies forum so it wont get lost.
okey doke? :)

Linstrum
08-04-2007, 02:16 AM
Awright, yeah! :-D Thanks!

montana_charlie
08-04-2007, 12:48 PM
Linstrum,
I am posting in this thread to avoid 'messing up' the other one with extraneous material.

There, you said, "Because a lot of our younger members are still in school I will try to make the math as easy as possible so everybody can have a shot at being able to use this or at least get an idea of what is going on."

Well...more than one forum member has been out of school for 40 years or more. If, during the interim, his most complicated calculations were to determine how many 80-pound hay bales are required to feed 60 pairs and two bulls for a day...that person will appreciate any simplicity you can instill in your explanations.

Further, you invited any and all 'math wiz'-es to reconfigure your formula for determining the actual amounts contained in an existing two-metal alloy.

Having a vaguely remembered recollection of that process, I could probably come up with something which would produce numbers...if given three days and reliable access to Google. But, I would have little confidence that they were correct numbers.

Please try to find time to do that...and add it to your other thread.

Bret4207
08-05-2007, 08:39 AM
Charlie- I'd say you need about 35 bales.

montana_charlie
08-05-2007, 11:52 AM
Charlie- I'd say you need about 35 bales.
You have it figured pretty close, Bret. But I would still like to see that formula so I can determine the 'ratio of the alloy'. You know...how much alfalfa - how much grass.
CM

Bret4207
08-05-2007, 12:50 PM
Gotta have percentage of protein, TDN, all the other stuff thats in the hay and then keep track of the animals gain. At least thats what the college boys say. I just feed them as much of what I got as they'll eat and hope for the best. HAR!

montana_charlie
08-05-2007, 02:46 PM
Gotta have...all the other stuff...then keep track of the animals gain.
True...for the feedlot guy. I'm just a cow/calf operation.
The calves will weigh a decent amount at market time if the mothers stay in good condition. So I just watch for 'bones'.

If I gave 'em 'as much as they'll eat'...I couldn't afford to keep 'em.
CM

joeb33050
08-06-2007, 07:55 AM
This chart is from the book, at http://sports.groups.yahoo.com/group/CB-BOOK/, Chapter 3.2. This explains how and why to measure specific gravity of lead alloys. Measuring the specific gravity of the alloy gives a RANGE of tin and antimony percentages. If we measure the HARDNESS of the alloy, and go to the chart in 3.2 in the book showing BHN at various tin and antimony percentages, we'll have a pretty good guess at the alloy composition.
joe brennan





I have attached a chart that I downloaded a while ago that has a chart of various alloys and their specific gravity. I have the full article if anyone is interested. I think this originally came from the Cast Bullet Organization.



The chart shows that the sample was somewhere between 15% antimony and no tin and 12% tin with no antimony. You look for the specific gravity in each column/row and then read the % of both tin and antimony that makes up this specific gravity. Unfortunately, the chart can't tell you which of the dozen or so mixes you have, but at least you have a range of possible values.

Either one is probably worth 50 cents per pound!

John

Tom Myers
08-06-2007, 10:01 AM
I realize that this may produce some controversy but I believe that the situation should be addressed.

It seems that in many instances, when calculating the specific gravity of an alloy, the procedure used is to add the percentage of the specific gravity of each individual component metal to arrive at the specific gravity of the alloy.

Like this:

5% of the specific gravity of tin + 95% of the specific gravity of lead = the specific gravity of the alloy
= 5% / 100 x 7.337 + 95% / 100 x 11.345 = 11.1446
11.1446 = The Specific Gravity of the Alloy;

That is the way that I used to do it and whenever I would attempt to calculate out weights of blended alloys, things would never come out right.

While searching for an answer, I managed to find an excerpt from an old Gold and Jewelry publication of some sort and also an old article written for an assayers journal. Each instance of the writings indicated that the percentage of the RECIPROCAL of the specific gravity of each metal should be added together to produce the RECIPROCAL of the specific gravity.

(To find a Reciprocal of a number - divide 1 by the number )

Like This:

5% / 100 x 1 / the specific gravity of tin + 95% / 100 x 1 / the specific gravity lead = 1 / by the specific gravity of the alloy

5 / 100 x 1 / 7.337 + 95 / 100 x 1 / 11.345 = 1 / 0.090552

1 / 0.090552 = 11.0434 = Specific Gravity of the alloy


When I started using this method, everything began to fall in place and I began to achieve accurate results when I was calculating and mixing my alloys.

I shamelessly paraphrased one of the articles (I cannot find the references of the old articles any where) and placed it on my website at http://www.uslink.net/~tom1/specific-gravity.htm

To simplify matters a little more, I reduced the equations for determining the percentages of tin or antimony in an alloy with a known specific gravity down to these two functions.

TIN
Let TSG = the specific gravity of a tin/lead alloy
or
ANTIMONY
Let ASG = the specific gravity of an antimony/lead alloy

Then:
2076.803 / TSG - 183.059 = the percentage of tin in the alloy
or
1636.416 / ASG - 144.241 = the percentage of antimony in the alloy

Tom Myers
Precision Ballistics and Records (http://www.uslink.net/~tom1)

joeb33050
08-08-2007, 05:16 AM
Tom is absolutely correct in this, this method of calculating is called the "harmonic mean", weighted, and I found several websites that used this calculation. My table in the book was wrong, it now has been changed and appropriate credit has been given. I'll post the revised table later.
Thanks;
joe brennan



I realize that this may produce some controversy but I believe that the situation should be addressed.

It seems that in many instances, when calculating the specific gravity of an alloy, the procedure used is to add the percentage of the specific gravity of each individual component metal to arrive at the specific gravity of the alloy.

Like this:

5% of the specific gravity of tin + 95% of the specific gravity of lead = the specific gravity of the alloy
= 5% / 100 x 7.337 + 95% / 100 x 11.345 = 11.1446
11.1446 = The Specific Gravity of the Alloy;

That is the way that I used to do it and whenever I would attempt to calculate out weights of blended alloys, things would never come out right.

While searching for an answer, I managed to find an excerpt from an old Gold and Jewelry publication of some sort and also an old article written for an assayers journal. Each instance of the writings indicated that the percentage of the RECIPROCAL of the specific gravity of each metal should be added together to produce the RECIPROCAL of the specific gravity.

(To find a Reciprocal of a number - divide 1 by the number )

Like This:

5% / 100 x 1 / the specific gravity of tin + 95% / 100 x 1 / the specific gravity lead = 1 / by the specific gravity of the alloy

5 / 100 x 1 / 7.337 + 95 / 100 x 1 / 11.345 = 1 / 0.090552

1 / 0.090552 = 11.0434 = Specific Gravity of the alloy


When I started using this method, everything began to fall in place and I began to achieve accurate results when I was calculating and mixing my alloys.

I shamelessly paraphrased one of the articles (I cannot find the references of the old articles any where) and placed it on my website at http://www.uslink.net/~tom1/specific-gravity.htm

To simplify matters a little more, I reduced the equations for determining the percentages of tin or antimony in an alloy with a known specific gravity down to these two functions.

TIN
Let TSG = the specific gravity of a tin/lead alloy
or
ANTIMONY
Let ASG = the specific gravity of an antimony/lead alloy

Then:
2076.803 / TSG - 183.059 = the percentage of tin in the alloy
or
1636.416 / ASG - 144.241 = the percentage of antimony in the alloy

Tom Myers
Precision Ballistics and Records (http://www.uslink.net/~tom1)

joeb33050
08-12-2007, 08:19 AM
First, please remove the chart above-it's mine, I made it, and its' WRONG.
If you go to the book at http://sports.groups.yahoo.com/group/CB-BOOK/ look in FILES and look in 3.2 BULLET CASTING METALS; the corrected chart is there. The chart is copied from an EXCEL workbook called SPECIFIC GRAVITY CALCULATOR, look way down in FILES. The EXCEL workbook and chapter 3.2 were fixed after reading LINSTRUM's and Tom Myers's explanation here.
Now, as to the salt/water business, does a volume of lead and a volume of tin = 2 volumes of alloy?
I did an extensive search on this matter when writing that chapter, and came to the conclusion that probably the result is a little less than 2 volumes of alloy. But, the literature and references are fuzzy at best. Values for hardness and specific gravity of lead, tin and antimony and alloys show a lot of variation, or at least more than I'd have suspected.
The S.G. method is a guess, an educated guess, but a guess at the components of an unknown alloy. It's better than nothing, but not precise at all.
joe brennan

garandsrus
08-12-2007, 09:00 AM
Joe,

I can't remove the post with the chart as it's no longer editable... If one of the system administrators can do it, that would be great.

I have read your book and liked it very much!

John