Re: why is delta Q used for heat

Jane,

Before I give you the answer, let me tell you how I found it.

First, I looked in one of my old Chemistry textbooks where heat is
discussed.  Generally, there are references at the end of the Chapter
for further reading on the subject.  Then I looked up specific books
on the electronic card catalog system for U. Penn's library.  In the
process, I found a better source for historical sorts of questions.

If you just look under Physical Sciences or Thermodynamics (or any
other broad subject), there are generally more specific subheadings
you can sort through.  In this case I looked up "Thermodynamics--
History" and found this:

	Cardwell, Donald, S. L.
	"From Watt to Clausius; the rise of thermodynamics in the
		early industrial age"
	Ithaca, N.Y., Cornell University Press [1971]
	Call Number: TJ265.C33

The point of going to this source is to find the original reference
where "q" was used for heat, or at least a historical discussion of
its introduction.  It turns at the Cardwell book didn't give us the
answer, but did reference the original work:

	Lavoisier, Antoine L., & Laplace, Pierre S.
	"Memoir on heat" ("Memoir sur la Chaleur")
	English translation:  New York; N. Watson Academic
		Publications, 1982 (originally published in
		French, 1780)
	QC253.L313

It is a groundbreaking work, so most BIG libraries should have a copy
in their Special Collections section.  So, I went and looked at the
original.

Here's what Lavoisier and Laplace had in mind.  They were trying to 
describe in a quantitative way what happens when you mix two substances
at different temperatures.  Their original experiments involved heating
up different materials (metals, oils, all kinds of things) and then 
mixing it into a bucket of water at a different temperature.

	Warm Body:
	m = the mass of body 1
	q = the quantity of heat which can raise the temperature
		of the body by one degree.
	a = the reading of the thermometer

	Cool Body (usually water in their experiments):
	m' = the mass of body 2
	q' = the quantity of heat which can raise the temperature
		of body 2 by one degree.
	a' = temperature of body 2

Finally, b was defined as the end temperature after mixing the two 
materials together.  They came up with the relations:

	Heat lost by body 1 = mq(a-b)
	
	mq(a-b) = m'q'(b-a')

	(q/q') = [m'(b-a)] / [m(a-b)]

They didn't talk about heat as a physical picture, just as a "quantity"

So, q stands for quantity, the quantity of heat which can raise the 
temperature of the body by one degree.

(In French, if you want to impress your teacher, "C'est la quantite' q 
de chaleur qui peut e'lever d'un degre' la temperature d'une liver
de cette quantite' de chaleur perdue.")

I hope that covers it.

Sincerely,
Dr. Jim Kranz