FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
natural units (steve alexander)
slaking heat ("Spencer W. Thomas")
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JANITORs on duty: Pat Babcock (pbabcock at hbd dot org), Jason Henning,
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Date: Mon, 23 Feb 2009 05:24:04 -0500
From: steve alexander <steve-alexander at roadrunner.com>
Subject: natural units
Greg Lehey notes ,
> So what time units do you use?
>
> In any case, this is incorrect. The metric system was developed with
> 'time' based on decimal divisions of the solar day. The time you talk
> about is in such universal usage that it ovverrode the more rational
> metric approach, which was never introduced as part of the metric
> system.
>
Not quite. There was a French decimal day in use for just a few years
before the metric convention, but it was suspended about the same time.
The original metric system had no time unit ! The seconds defined as
1/86400 of the mean solar day was adapted in 1954 as the original metric
time unit, but the second was used w/o complete definition before that.
The second may be almost universal but even in scientific journals we
see time in minute, hours, days etc - non-metric units. The 100kph
signs on the roadside aren't metric for the same reason.
>> This is the system that was developed with a 'length' based on a bad
>> estimate of the distance from equator to pole of some mostly
>> harmless planet, ...
>>
>
> Well, again no. It was originally conceived with a length based on
> the length of a pendulum with fixed period. That definition lasted
> about 10 months, to be replaced by the one you mention, which lasted 8
> years, to be replaced by yet another one in December 1799.
>
> In any case, this is the definition of the unit, not the usage. Using
> the technology of 220 years ago, what more elegant unit would you
> propose?
>
The pendulum (~0.93 meter) was adopted by the French National Assembly
months before the French Academy of Sci chose 10^-7 earth quadrants - so
there is a question if whether the pendulum was ever part of "the metric
system". A provisional meter estimated at 10^-7 quadrants was
developed in 1793, and this was replaced in 1799 by a bar meant to be
the same 10^-7 quads but now acting as the (then) official definition.
>> where temperature is expressed in units based on the phase change of
>> H2O at some ambient pressure
>>
>
> ... directly related to its most normal usage. Again, how does this
> differ from other definitions of the day? You omit to point out that
> the definitions have long since been replaced by corresponding
> definitions based on absolute physical constants.
>
No not physical constant unfortunately. The original silly units have
just been replaced with new silly units of about the same size.
Instead of a second defined by the 1/86400 of an earth day we have a
second defined as several zillion cycles of the hyperfine oscillation of
Cesium where the number is mumbo-jumbo for "almost the old second" ....
tho' later papers suggest the Cs must be in the ground state at absolute
zero, and further conditions will be added as needed. The standard is
fluid ! The constants change. This is from their legacy as poorly
defined quantities.
I'll give props to to the current temp definition, but the mole has
issues resolved in the 1980s, the second has defintional problems
related to the state of cesium133. The meter is dependent on the lousy
second. Sorry Greg, but these "physical constants" are destined to
continue changing just as they have over the past 40 years.
AJ adds ....
> Temperature is defined in terms of absolute 0 and the triple point of
> water neither of which is dependent on pressure. The temperature scale
> (ITS-90) is, thus, defined in terms of fundamental physical constants.
>
This was adopted in 1967, where a Kelvin is 1/273.16 of the
thermodynamic temperature of the triple point of water. So why would
absolute zero and the triple pt be divided into 273.16 units of measure
? B/c it refers back to the Celsius unit which preceded it obviously
and they again tried to make 1K "almost the same" as 1C. A foolish if
practical consistency.
> The meter is defined as the distance light travels in a vacuum in
> 1/299792458 sec and thus related to a fundamental physical constant -
> the hyperfine transition of the outer electron in the cesium atom in a
> field free environment.
>
That's the current meter definition, but before that a certain number of
wavelengths of something or other.
and this definition is a great example of the problem.
meter = C * 1/299792458 sec.
second = 9,192,631,770 Periods transition between the two hyperfine
levels of the ground state of the caesium-133 atom.
So to make this definition come out to these nice integer values, which
"constant" has changed ? (the meter in this case). Before that the
second was tweaked to the cesium periods. Every time the definition
changes the unit changes slightly. The constants are inconstant. A
meter is exactly the length the CGPM thinks it should be this decade,
but it's always close enough to the old value to avoid everyday
problems; yet different enough to bugger-up old textbooks and tables.
Then we have the amp ,volt, coulomb system which is IMO has inferior
definitions to the gaussian-cgs statvolt statamp, esu system but .. The
seven base units should overconstrain the dimensions too, and this shows
up in the derived electromagnetic units I think.
> That brings us to the kilogram. [...] As
> this is disquieting to scientists there is effort afoot to tie the
> kilogram to a fundamental physical constant (which will probably be
> Planck's constant).
>
But we can construct fundamental units from some of the very basic
physical constants - the unit charge, planks constant, gravitational
constant, c - there is no need for the silliness of committee
definitions for units any longer. You can't revise the definition of
gravitational constant or the unit charge.
To answer Greg's questions, I'm partial to the systems called "Plank's
units" here
http://en.wikipedia.org/wiki/Natural_units
-S
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Date: Mon, 23 Feb 2009 10:07:50 -0500
From: "Spencer W. Thomas" <hbd at spencerwthomas.com>
Subject: slaking heat
Slaking heat appears to have been first mentioned in the HBD in 1992:
http://hbd.org/hbd/archive/973.html#973-25
http://hbd.org/hbd/archive/1036.html#1036-1
These references include no explanation. It came up again in 1995,
1997, 1998, 1999, but then dropped off the radar until now.
I found an abstract of a 1910 article in the J Inst of Brewing on the
topic, which seems to be an early description of the concept with
experimental values derived:
The Specific Heat of Malt and the Calculation of the "Initial Heat"
of the Mash. H. T. Brown. (J. Inst. Brewing, 1910, 16,
112-129.)--The author,
in a previous communication on this subject (J. Inst. Brewing, 1899,
5, 335), had
assumed that dry malt must be assigned a specific heat of at least
0.52 (instead of
the value usually given of 0.42), from the data he obtained when
experimental
mashes were made, if allowance be made for the whole of the heat
evolved when dry
malt is mixed with cold water-"slaking heat." More recent work shows
that
0.38 is the true value for dry malt, rising to 0.41 for malt
containing 6 per cent.
water, and reasons are given for showing that in reality only one
half the value of
the " slaking heat " is available when malt and hot water are mixed.
This slaking
heat varies in a direction inverse to the moisture content of the
malt. The amended
formula for the calculation is appended :
I = (St+RT)/(S+R) + 1/2 H/(S+R)
S =specific heat of the malt (0.38 if dry, otherwise obtainable frem
the table).
t =temperature of the malt.
R = weight of'water corresponding to unit weight of malt.
T =temperature of the water.
H=the slaking heat of the malt in cold water expressed in
grm.-calories F. (obtained from table).
I = the initial temperature of the mash.
I also found a more recent mention in a Google Book entry:
http://preview.tinyurl.com/c34mh2
Brewing: Science and Practice
By Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes, Roger Stevens
Edition: illustrated
Published by CRC Press, 2004
ISBN 0849325471, 9780849325472
=Spencer in Ann Arbor
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End of HOMEBREW Digest #5511, 02/23/09
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