I'm about to see some of the original kilogram standards. Is that right?

Patrick: You are, you are.

When were these made?

Well the originals were made in the 1880s.

There were 40 of them that were brethren of the

International prototype kilogram

and these 40 were distributed to the signatories

of the Treaty of the meter and the

United States was given two, K4 and K20.

What was this meter agreement?

The treaty of the meter?

Yeah, what is that?

It's the modern-day foundation of the metric system.

So the U.S. signed that?

The U.S. signed it.

As if they were going to become metric?

Yes.

A little known secret and I'll tell you something else

that all the units that we commonly use

like feet and gallons and so on are

actually defined in terms of metric units.

So it's just a little translation

that we do here but our country is

actually on the metric system.

[Laughter]

Doesn't that seem crazy?

Yes!

Isn't that insane that like you base all of these measurements on the metric

system and then you add a conversion

factor and then later some people have

to convert back.

Yes, it's stupid.

[Laughter]

Are you allowed to say that?

It's true.

So can we see it?

sure sure

What do we have to do?

This requires that we go through

some high-security gear and also that

would be somewhat clean in what we do

so I'll have to ask you to put on some

booties here.

Let me see if I can do this

all right so, did I do it?

Yep, there you go.

straight back, all the way there you go.

This is the first

BootieButler that I've ever...

I'm a big fan.

This is the first layer.

Secret code

I'm going to show you two I'm going to

show you one of the originals and I'm

going to show you a more modern version

This is K 20.

Oh my goodness that is like the

original kilogram mass standard of the US.

That's right.

I never thought I would

get this close to it

virtually every mass that has been

accurately weighed in the US over the

past hundred and thirty years can trace

its measurement back to this one

kilogram hunk of 90 percent platinum 10 percent iridium.

Iridium makes the alloy much

harder than pure platinum and both

elements were selected for their high

density and resistance to oxidation this

kilogram was created in the same way at

around the same time as an object which

to this day remains the definition of

the kilogram an identical cylinder

stored in a basement vault on the

outskirts of Paris.

If you look straight

down from the top you can maybe see K 20

doesn't have a very nice finish on it

compared to the more modern prototypes

here's K 92 so it's got a much higher

polish on it different manufacturing

techniques absolutely no swirls it is a

really like beautiful looking specimen

yes it is I mean is there a reason why

you want it to look so beautiful?

well you want it not to be very rough

because roughness increases surface area

surface area increases the probability

that you will get contaminants on that

will change the mass of the entire thing

how much is it worth

well monetarily the new ones are about

$100,000 a piece if you were to buy one

oh my goodness so but if you think about

K 20 K for with about 130 years of

history they're priceless you could

never replace them the purpose of this

room then is to share the precise mass

of K 20 with anyone who wants to make a

measurement without sharing K 20 itself

what we do in this suite here is we

transfer the definition of the kilogram

from the platinum-iridium prototypes to

stainless steel secondary standards and

you can tell that they're a lot bigger

and the platinum-iridium prototypes and

that's because of the relative

difference in density the density of

stainless steel is about 8 grams per

cubic centimeter whereas the density of

platinum iridium is about 21.5 grams per

cubic centimeter so there's all of the

three times difference in density which

tells you why this is so much bigger in

volume and that creates a problem

ordinarily we don't worry much about the

buoyant force that is the upward force

on every object in the atmosphere equal

to the weight of air it displaces but

since the volumes of these masses are so

different a stainless steel object that

has around the same mass as k20 can have

its weight reduced due to buoyancy by

around 110 milligrams

the precise amount depends on the

temperature pressure and humidity of the

air that's why the mass comparator

itself is inside of a chamber here

that's isolated from the outside world

so that the temperature remains

relatively stable I'm the humidity the

same pressure is by far the biggest

contributor to air density so we don't

want it changing all over the place with

the weather the problem scientists are

having with the kilogram now is much

bigger than weather fluctuations it's

something they discovered when all the

original kilograms were returned to

Paris for a weigh-in including k20 how

did it get there it gets there by a

person hand carrying it each prototype

gets taken out of the bell jar and put

in its container how do we sound after

we get it in there all nicely secured

then we wrap the whole thing in bubble

wrap and put it in a camera bag and

sling it over our shoulders don't let it

out of our sight it sounds a little

casual so you actually like while you're

on the plane do you put it in like the

overhead stretch

know it stay just at all times like it's

a you know the nuclear football codes

were setting off a nuclear weapon and

you never have any scares while you're

carrying the only scare comes that

somebody wants to see it like a customs

official I've never had to open it

although I had a kind of a scary moment

at one time when they asked me what it

was made of and I told them it was

platinum iridium and somebody heard the

word iridium and connected that with

radioactivity no no and kind of you know

flew off the handle a little bit and I

had to calm them down on the shoreland

that it wasn't radioactive there was no

threats going on here

the real threat was the unreliable

weight and the kilogram mass standard

what they do is a series of comparisons

they compare every one of those with the

International prototype kilogram using

that data and plotting it it looked as

if there had been a change in the

International prototype that made it

about 50 micrograms heavier than one

kilogram now over the course of a

hundred years all right

but the interesting thing is if one

looks at the data that was recently

taken at the end of 2013 international

prototype kilogram did not show an

increasing mass telling me for several

decades it was gaining mass and also on

the stop which you know I find that hard

to explain but it seemed like all of the

40 masses in to be somewhat diverging at

that weigh-in they went different ways

they went in different directions yes so

that some changed a lot some changed

little some hardly changed at all but

it's hard to tell I mean they could

we'll all be changing a lot but because

all you can tell is the difference

between them they've already married

all that matters is the difference

between them and the International

prototype because the International

prototype is the only thing you need the

only thing that you really know because

it's defined as one kilogram

right but I mean the outside of that

definition there's a chance it could

have gained you know five grams as long

as they all gain five grams you know I'm

having these ridiculous obviously it's

ridiculous but the point is they could

have all been gaining or they could all

been losing right it's a relative

measurement and that's the weakness of

the system

and that's why as of 2018 the kilogram

will no longer be defined as the mass of

a metal cylinder why if you want to find

out how the kilogram will be redefined

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