The Assay
First thing you must do is to make a chart. I know you think you can remember it all but please do it this way. This is the way the pros do it and you
ain’t likely to improve on it.
All volumes in milliliters (ml)
The last tube is for the unknown sample, any amount up to 7.5 ml.
I have to say here that I do not like this protocol. It’s not mine, I got it from somewhere in the literature. Offhand I do not recall who devised this assay
but I can tell you a little about him. He was an inorganic chemist. Why? Because inorganic chemists love to use large reaction mixtures. They hate to try
to measure anything less than 10 ml. A biochemist on the other hand hates to try to measure any amount more than 5 ml. The difference is that
chemists rarely learn to use a pipette. They prefer to measure in graduated cylinders etc. However, this is a perfectly good assay and the large volume will
probably be easier for you to deal with until you get the hang of using a pipette.
To get on with the assay, set up your test tubes in a row. Now go to the first horizontal line on the chart to see how much of what to add to each
tube. Make the additions, and then drop down to the second line, etc.
After you add the ether, take a piece plastic or a stopper to seal the test tube mouths and shake it 25 times. Put it back in the rack and go to the next.
When all the tubes have been shaken you will note that the ether layer is now floating on the water layer. Also the ether (or benzene) will have a
reddish/blue color. That’s what you are looking for. Your # 1 tube should be weakly colored and the color intensity should get progressively darker as
you go to the tenth tube. The eleventh tube is your sample. Now simply compare the color in the sample tube to the others and select the tube that
most closely matches that of the sample. Now you know very close to how much gold is in the sample because you have matched it to a reaction with a
known amount of gold. Now you will have to a little simple arithmetic to calculate the gold in your original ore sample.
How to Use a Pipette
Why should you want to know how to use a pipette when you probably don’t even know what a pipette is? Well, I think you will find that a few
pipettes around the Basement will be a tool that you will learn to use a lot. They are very convenient and useful tools for accurately measuring any
liquid.
So what are they anyway? As usual, its not as simple as saying "it’s a glass tube". Actually there are three types of pipettes that are of interest to us.
First is one called a "measuring pipette". All these pipettes come in sizes from 0.1 ml to as large as 25 ml. Lets use a 5 ml for example. This thing is, in
effect, a glass or plastic tube with the tip restricted and graduation marks at, usually, 0.1 ml increments with 0 at the top end and 5.0ml at the bottom.
This type has an etched line near the bottom end that will be marked 5.0ml. If you fill the pipette to the 0 mark and then allow the liquid to drain out
until it reaches the 5ml mark you will have pipetted exactly 5.0ml. That’s right, accurate to at least 0.1ml.
The next type is called a "serological" pipette. At first glance it appears exactly like the measuring pipette, however, upon closer inspection, you will note
that it is graduated all the way to the tip. There are two main types of these. If you look at the top of the pipette you will probably find an etched ring.
If so, you have a "blowout" pipette. If you want to put entire 5 ml into a flask you will have to blow the last drop out. If you don’t see the etched ring
at the top it is a "drain out" pipette. With this type you must simply touch the tip to the side of the flask to allow the last drop to flow out. Don’t try
to cheat, that is the way they are calibrated.
The third type is called a "volumetric" pipette. This type has no intermediate calibrations. If it is a 5ml, you can only measure 5 ml. You cannot measure
4.4ml, for example. These are not as generally useful as the first two. They are easily recognized by the fact that it has a "bulb" or bulged section in the
glass stem.
There are many other types of pipettes designed for special purposes. For example a "milk pipette" is, for example, calibrated at 1ml and at 1.1ml.
nowhere else. A "lamda" pipette is a volumetric type but it can accurately deliver volumes of as little as 1.0 microliter. That’s right, 1/1,000,000 of a liter.
Anyway, you get the idea.
In case I lost a few of you, the drawings below should help visualize what I am talking about;
Yeah, I know, I’m no artist. Can’t sing either! But, I do know how to use a pipette. Used them probably 200 times a day for 30 years. So what’s the big
deal about pipettes? You just suck up some liquid, drain it out to the zero mark, and then drain out as much as you want, right? Absolutely right! The
question is, can you do it? I know, I know, of course you can. Would you trust yourself to suck up some sulfuric acid or cyanide without getting a
mouthful? I might do it in a pinch but I’ve pipetted about 10-20 million times more than you have. And, even for me it ain’t a good idea. Fine, if you are
dealing with water, salt solution, alcohol, etc, if you get a snoot full it’s no big deal but with nitric acid, aqua regia etc, it could be a big deal. I guess we
gotta skin that cat too. I am the nightmare of all cats in the world! Fortunately for us some enterprising folks have devised "safety pipettors". There are
numerous designs of these devises but there is one that for our purposes seems to be the most practical and economical. It’s sort of hard to describe
but it is basically a rubber bulb attached to the end of the pipette that does the sucking for you. It has three little "squeeze valves" on it. Three valves?
Sounds complicated, but it’s not. Since I can’t describe it very well, I’ll make another of my computer enhanced, Michelangelo quality drawings. Hang on
to this. In a hundred years it will be worth millions!
So, how do we run this hi-tech device? I know you are all waiting with your tongues hanging out for me to tell you. Well, you simply stick the pipette in
the bottom end as indicated. Now you squeeze the top valve and also squeeze the bulb to create suction in the bulb. Release the valve and you have
trapped some energy as vacuum in the bulb. Now you put the end of the pipette in the liquid that you want to measure/transfer and squeeze the
second valve, the one in direct line top to bottom, just below the bulb. You will find that the liquid will start to rise in the pipette in a very ‘controlled"
manner. Let the liquid rise to above the 0 mark on the pipette. Now you switch to the 3rd valve, the one off to the side. Squeeze it gently and you will
find that the liquid will start to slowly drain from the pipette. When it gets to exactly 0, release the valve. Now you can stick the pipette in whatever
vessel you choose, squeeze the side valve again and deposit whatever amount you want into the receiving vessel. If you are using a "blowout pipette
you have to blow out the last drop, right? To do this simply put one finger over the end of the side-valve and squeeze the valve. It will blow out the last
drop.
Now you know all there is to know about pipetting, right? No, you can’t get off that easy. Forget the safety pipettor for a moment. You will definitely
not want to use this device all the time, so you must learn to pipette by mouth also. There is only one trick you must know to accomplish this. If no one
ever tells you how, you might spend the rest of your life trying to pipette by mouth. I am going to divulge this secret to you at absolutely no cost, not
even postage and handling. I’m a super-nice guy, ain’t I. If I should hand you a pipette and a beaker of water and say "transfer 2.6 ml into this test
tube"; I can tell you exactly how you are going to try to do it. O.K., there might be 5% of you who would get it right the first time. The first thing you
will do is to grasp the pipette in your hand with four fingers, pinky to index, holding it. You will suck up some water, then simply put your thumb over
the top end of the pipette to keep the water from escaping. Now you will try to relieve a little pressure on your thumb and let the water flow out of the
pipette. This is the way everyone try’s to do it! Fact is, It ain’t gonna work! If there is anyone out there in the whole world that can do it that way, I’ll
pay your airfare and hotel bill to come to CR and show me. If you can’t do it, I don’t pay.
So, if we can’t do it that way how the hell do we do it? Well, we do it like the pro’s. Standard chemists can’t do this. Only microbiologists and
biochemists. Get a pipette or just a small diameter piece of tubing; grasp it with your pinky, index, and middle finger on one side and your thumb on the
other. That ain’t hard but I’ll bet you it’s not the way you really want to do it. That leaves your index finger free to cap the top of the pipette. THAT IS
THE WAY YOU DO IT! Practice this for an hour and you will find that you can control the liquid to at least 0.1 ml. I can control it to 0.01 ml, but I’ve had
lots of practice. Try it with your thumb too. Just to see if you can get a free trip to Costa Rica off me. If you depend on your thumb, I don’t think you
will ever see the beautiful "Rich Coast".
There are many other methods to do colorimetric assays of gold. In fact you can simply dissolve gold in an HCl solution, add tin (stannous chloride) and
the gold will precipitate as a colloid of purple gold particles (purple of Cassius). This has been used for thousands of years to assay gold. I will find a
method or devise my own and post it ASAP. Right now my plate is pretty full so I have to post what I can and hope that it helps a little.
Ain’t all this stuff Fun!!!
First thing you must do is to make a chart. I know you think you can remember it all but please do it this way. This is the way the pros do it and you
ain’t likely to improve on it.
All volumes in milliliters (ml)
The last tube is for the unknown sample, any amount up to 7.5 ml.
I have to say here that I do not like this protocol. It’s not mine, I got it from somewhere in the literature. Offhand I do not recall who devised this assay
but I can tell you a little about him. He was an inorganic chemist. Why? Because inorganic chemists love to use large reaction mixtures. They hate to try
to measure anything less than 10 ml. A biochemist on the other hand hates to try to measure any amount more than 5 ml. The difference is that
chemists rarely learn to use a pipette. They prefer to measure in graduated cylinders etc. However, this is a perfectly good assay and the large volume will
probably be easier for you to deal with until you get the hang of using a pipette.
To get on with the assay, set up your test tubes in a row. Now go to the first horizontal line on the chart to see how much of what to add to each
tube. Make the additions, and then drop down to the second line, etc.
After you add the ether, take a piece plastic or a stopper to seal the test tube mouths and shake it 25 times. Put it back in the rack and go to the next.
When all the tubes have been shaken you will note that the ether layer is now floating on the water layer. Also the ether (or benzene) will have a
reddish/blue color. That’s what you are looking for. Your # 1 tube should be weakly colored and the color intensity should get progressively darker as
you go to the tenth tube. The eleventh tube is your sample. Now simply compare the color in the sample tube to the others and select the tube that
most closely matches that of the sample. Now you know very close to how much gold is in the sample because you have matched it to a reaction with a
known amount of gold. Now you will have to a little simple arithmetic to calculate the gold in your original ore sample.
How to Use a Pipette
Why should you want to know how to use a pipette when you probably don’t even know what a pipette is? Well, I think you will find that a few
pipettes around the Basement will be a tool that you will learn to use a lot. They are very convenient and useful tools for accurately measuring any
liquid.
So what are they anyway? As usual, its not as simple as saying "it’s a glass tube". Actually there are three types of pipettes that are of interest to us.
First is one called a "measuring pipette". All these pipettes come in sizes from 0.1 ml to as large as 25 ml. Lets use a 5 ml for example. This thing is, in
effect, a glass or plastic tube with the tip restricted and graduation marks at, usually, 0.1 ml increments with 0 at the top end and 5.0ml at the bottom.
This type has an etched line near the bottom end that will be marked 5.0ml. If you fill the pipette to the 0 mark and then allow the liquid to drain out
until it reaches the 5ml mark you will have pipetted exactly 5.0ml. That’s right, accurate to at least 0.1ml.
The next type is called a "serological" pipette. At first glance it appears exactly like the measuring pipette, however, upon closer inspection, you will note
that it is graduated all the way to the tip. There are two main types of these. If you look at the top of the pipette you will probably find an etched ring.
If so, you have a "blowout" pipette. If you want to put entire 5 ml into a flask you will have to blow the last drop out. If you don’t see the etched ring
at the top it is a "drain out" pipette. With this type you must simply touch the tip to the side of the flask to allow the last drop to flow out. Don’t try
to cheat, that is the way they are calibrated.
The third type is called a "volumetric" pipette. This type has no intermediate calibrations. If it is a 5ml, you can only measure 5 ml. You cannot measure
4.4ml, for example. These are not as generally useful as the first two. They are easily recognized by the fact that it has a "bulb" or bulged section in the
glass stem.
There are many other types of pipettes designed for special purposes. For example a "milk pipette" is, for example, calibrated at 1ml and at 1.1ml.
nowhere else. A "lamda" pipette is a volumetric type but it can accurately deliver volumes of as little as 1.0 microliter. That’s right, 1/1,000,000 of a liter.
Anyway, you get the idea.
In case I lost a few of you, the drawings below should help visualize what I am talking about;
Yeah, I know, I’m no artist. Can’t sing either! But, I do know how to use a pipette. Used them probably 200 times a day for 30 years. So what’s the big
deal about pipettes? You just suck up some liquid, drain it out to the zero mark, and then drain out as much as you want, right? Absolutely right! The
question is, can you do it? I know, I know, of course you can. Would you trust yourself to suck up some sulfuric acid or cyanide without getting a
mouthful? I might do it in a pinch but I’ve pipetted about 10-20 million times more than you have. And, even for me it ain’t a good idea. Fine, if you are
dealing with water, salt solution, alcohol, etc, if you get a snoot full it’s no big deal but with nitric acid, aqua regia etc, it could be a big deal. I guess we
gotta skin that cat too. I am the nightmare of all cats in the world! Fortunately for us some enterprising folks have devised "safety pipettors". There are
numerous designs of these devises but there is one that for our purposes seems to be the most practical and economical. It’s sort of hard to describe
but it is basically a rubber bulb attached to the end of the pipette that does the sucking for you. It has three little "squeeze valves" on it. Three valves?
Sounds complicated, but it’s not. Since I can’t describe it very well, I’ll make another of my computer enhanced, Michelangelo quality drawings. Hang on
to this. In a hundred years it will be worth millions!
So, how do we run this hi-tech device? I know you are all waiting with your tongues hanging out for me to tell you. Well, you simply stick the pipette in
the bottom end as indicated. Now you squeeze the top valve and also squeeze the bulb to create suction in the bulb. Release the valve and you have
trapped some energy as vacuum in the bulb. Now you put the end of the pipette in the liquid that you want to measure/transfer and squeeze the
second valve, the one in direct line top to bottom, just below the bulb. You will find that the liquid will start to rise in the pipette in a very ‘controlled"
manner. Let the liquid rise to above the 0 mark on the pipette. Now you switch to the 3rd valve, the one off to the side. Squeeze it gently and you will
find that the liquid will start to slowly drain from the pipette. When it gets to exactly 0, release the valve. Now you can stick the pipette in whatever
vessel you choose, squeeze the side valve again and deposit whatever amount you want into the receiving vessel. If you are using a "blowout pipette
you have to blow out the last drop, right? To do this simply put one finger over the end of the side-valve and squeeze the valve. It will blow out the last
drop.
Now you know all there is to know about pipetting, right? No, you can’t get off that easy. Forget the safety pipettor for a moment. You will definitely
not want to use this device all the time, so you must learn to pipette by mouth also. There is only one trick you must know to accomplish this. If no one
ever tells you how, you might spend the rest of your life trying to pipette by mouth. I am going to divulge this secret to you at absolutely no cost, not
even postage and handling. I’m a super-nice guy, ain’t I. If I should hand you a pipette and a beaker of water and say "transfer 2.6 ml into this test
tube"; I can tell you exactly how you are going to try to do it. O.K., there might be 5% of you who would get it right the first time. The first thing you
will do is to grasp the pipette in your hand with four fingers, pinky to index, holding it. You will suck up some water, then simply put your thumb over
the top end of the pipette to keep the water from escaping. Now you will try to relieve a little pressure on your thumb and let the water flow out of the
pipette. This is the way everyone try’s to do it! Fact is, It ain’t gonna work! If there is anyone out there in the whole world that can do it that way, I’ll
pay your airfare and hotel bill to come to CR and show me. If you can’t do it, I don’t pay.
So, if we can’t do it that way how the hell do we do it? Well, we do it like the pro’s. Standard chemists can’t do this. Only microbiologists and
biochemists. Get a pipette or just a small diameter piece of tubing; grasp it with your pinky, index, and middle finger on one side and your thumb on the
other. That ain’t hard but I’ll bet you it’s not the way you really want to do it. That leaves your index finger free to cap the top of the pipette. THAT IS
THE WAY YOU DO IT! Practice this for an hour and you will find that you can control the liquid to at least 0.1 ml. I can control it to 0.01 ml, but I’ve had
lots of practice. Try it with your thumb too. Just to see if you can get a free trip to Costa Rica off me. If you depend on your thumb, I don’t think you
will ever see the beautiful "Rich Coast".
There are many other methods to do colorimetric assays of gold. In fact you can simply dissolve gold in an HCl solution, add tin (stannous chloride) and
the gold will precipitate as a colloid of purple gold particles (purple of Cassius). This has been used for thousands of years to assay gold. I will find a
method or devise my own and post it ASAP. Right now my plate is pretty full so I have to post what I can and hope that it helps a little.
Ain’t all this stuff Fun!!!
Colorimetric Assay of Gold
Page 2
Page 2
Back one
page
page