Here's An Important (Skill Testing) Question

[Guest guest]

Hi folks:

Try this very difficult puzzle question:

Do potatoes have a specific gravity above, at, or below unity?

This may not seem to you like an important question, until I explain

to you, perhaps tomorrow, why I ask it. Then I think you may see why

it may be more important than it looks.

Rodney.

[Guest guest]

If the potato floats in water, SG is less than 1.0

If it sinks in water, SG is greater than 1.0

-- Warren

On 24 Jan 2004, Rodney wrote:

>

> Do potatoes have a specific gravity above, at, or below unity?

[Guest guest]

Hi Warren:

Yes, I tried that. Mine sank. Indeed just to check for myself, in

addition, I weighed one and also measured how much water it displaced.

S.G = 1.065 according to my calculations.

So it is surprising, and perhaps a little disconcerting, that the

USDA National Nutrient Database seems to believe otherwise. The

nutrient information the database supplies is, it says, for " '.5

cup' or '78g' " .

My understanding is that the official cup measure is equal to 236.6

mls. So '.5 cup' should be equal to 118.3 mls. IF that amount of

potato is supposed to weigh 78g then the S.G. of potato must be

believed to be about 0.66. Not only should the USDA's potatoes

float, they should float quite high in the water.

So the issues for us are, first, which of these two alternatives do

the nutrition data refer to (if either)? Second, possibly more

significant, since all our calculations are ultimaely based on the

data in this database, how many other errors are there? So do we

really know how many calories we are consuming?

Perhaps there is an alternative explanation. Maybe they used a

different species of potato? Or perhaps the water is different in

DC? Or maybe the S.G. of potato directly with latitude? (DC is quite

a bit south of here).

If they get around to answering my email I will let you know their

answer. But if this is an error (and the S.G. of potato is *** 60%

*** higher than they believe) then how seriously should we take the

rest of their data (that we make use of daily)?

Rodney.

> >

> > Do potatoes have a specific gravity above, at, or below unity?