[Avodah] Are there any chemists on Avodah?

[Hankman]

On Wed, Jan 05, 2011 at 02:37:52PM -0500, Hankman wrote:
: In the daf, 54a, the gemara brings a Tani Levi that describes the
: construction of the Misbeach. It was concrete-like in nature. It used
: forms much as we would today, aggregate of perfectly smooth stones
: (not to be felt when passing a fingernail over them) and some sort of
: matrix or "mortar" composed of some sort of mixture of sid, kunya and
: zefes, commonly translated as plaster or lime, lead, and pitch or
: bitumen. My question is about this "mortar" they used...

RMB wrote:

Mamcheh appears to mean "to disolve", according to Dr Jastrow. So I
don't a mixture, while accurate, is necessary the right mental image. I
think the lime is being used as an alkaline (wikipedia says it's caustic)
to reduce the lead. Bitumen and pitch, both tarry, are nore likely
to react with lead, but if we have a chemist rather than someone doing
web searches, it would help.

But back to the point, the lead was machah, and therefore not in a
shiny metal form when used for mortar. I'm figuring the verb holds
the answer, regardless of the chemical details.

CM asks:

Please explain two of the words you use. Tarry means ?, and "machah," is this a typo for mamcheh meaning to dissolve or some other word whose meaning I do not know? What is the right mental image? How do you get this from "dissolve"?

I strongly suspect (by analogy to other archeo concrete) that the lime is a primary component of the final mortar, and not just primarily used as an alkaline caustic to reduce (what reaction exactly do you mean?) the lead (although there of course could be some secondary chemical reactions going on?). Of course this is but a gut feeling without any proof. I doubt highly that the pitch was a primary component because then I imagine the mortar would be more in the nature of some sort of asphalt and be a problem at elevated temperatures of the fires on the surface of the mizbeach. I also doubt the primary component was the lead for the reasons I posted as my original questions in my first post. So if as you assume the lead is "reduced" (whatever that means) chemically, what is its function in the final mortar? Ditto, I was also looking for the function of the pitch (or bitumen).

So like you said, we wait for either a chemist or a material scientist to comment for a clearer explanation (if any be known).

Kol Tuv

Chaim Manaster
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