Dear Rabbi Kornfeld:
The Mishna on hatmana includes salt and sand as materials that could ADD heat to the wrapped object.
Ordinary salt (sodium chloride, NaCl) and ordinary sand (silica or silicon dioxide SiO2) don't do this, when moist or dry, as far as I know. Was there a different type of salt or sand that could add heat? Or was there perhaps a physical resemblance between salt or sand on the one hand and known heat-adding substances on the other hand, that could make one want to ban salt or sand as a precaution?
I've been puzzled by this for a long time. Thanks for your help!
Sincerely,
Robert A. Miller
Manager, Materials Development
TAFA Incorporated
Your question is a good one. Your suggestion that perhaps the Mishnah really means that a ban was made on salt and sand because they resemble some material that could add heat is insightful, and we would have liked to be able to suggest such an answer, but the straightforward meaning of the Mishnah and Gemara is that salt itself and sand itself add heat.
I brought your question to Dr. I. Asher, a fellow Dafyomi learner (who presently serves as special consultant to the Israeli Ministry of Science and Technology), who said that he was also bothered by the question, and the only thing that he and his Chavrusa could suggest was that either the nature of the physical world in the times of the Mishnah was different (which we do find in a number of instances; it could be that the salt the Mishnah mentions was Melach Sedomis ("Sodomite" salt), which may have had heat-inducing properties), or that we have to re-evaluate the definition of "Mosif Hevel" and say that perhaps it does not mean that the insulatory material actually adds heat, but that it is just extra-effective at conserving heat. This does not fully answer the question, though, as he pointed out, because (a) salt and sand are not known to be particularly effective at even doing that, and (b) this answer goes against the simple way of understanding "Mosif Hevel."
For now, then, it seems we will have to leave it as a question. If we find something, we will certainly let you know. And if you find something, please let us know.
All the best,
Yisrael Shaw
Dear Rabbi Kornfeld,
R' A.L. Lopiansky passed to me the query of Mr. Robert Miller concerning salt and sand as materials that can add heat in Hatmono.
1. Rock salt, which is quarried in many countries, contains approximately 1% of calcium sulfate. In a dry climate much, if not all, of the calcium sulfate will be in the form of Anhydrite. Anhydrite when mixed with water will produce copious amounts of heat. My impression is that even when Hatmono is made in dry salts some liquid could spill from the pot to the soil and heat from the Anhydrite is released. (This happens to me much too often.) Melach Sedomis is also a quarried salt. (A common name for Anhydrite is Plaster of Paris.) For the chemical composition of rock-salt see Encyclopedia Brittanica, 1972 edition, vol 19, page 957. 2. If instead of pure sand we understand sandy-soil then the heat of the sand is due to the bacterial decomposition of organic matter within the soil. Compost can get very hot. In Israel it is common to see vegetation sprouting from sand-dunes.Tzvi Weinberger
Rabbi Kornfeld AMV"S,
In reference to sand, Tosfos on 38b. Lo Yatminha states that when the Mishna prohibits covering an egg with sand it is talking about sand which was heated
in the sun which will then heat the egg. Perhaps the Rabbinin were gazher covering a vessel with sand because of sand which was heated in the sun whichwill heat an object it directly covers.
Kol Tov,
Yehudah Relis
We must say that the sand and salt were used for insulation by moistening
them. This was such an obvious fact that the Gemora did not need to explain
it.
A possibility:
I remember reading (I think in Noga Hareuveni's "Mibar Bemoreshet
Yisrael"), that the Eshel tree in the desert, uses a trick of putting out salt along
it's branches (or perhaps it's leaves). It gets rid of the excess desert salt, but more interesting is the fact
that in the morning there are large dew drops in the salt, received from the
air. During the day, it is always cool under the Eshel, which is one reason
Dr. Reuveni (Noga's father) had advised the British to plant Eshel trees
along the southern railways, which they did.
So maybe mosif hevel is the fact that it stores the water from the air,
and when you put the food in the salt/sand it "adds steam" to the food.
Or it could be (on the line of "just extra effective at conserving heat")
that salt and sand are extra good at keeping the food steamy.
It may be similar to the thermos effect of snow (which as far as I know is a true effect).
If you are very interested, I could help anyone interested set up an
experiment.
It has been a long time since my chemistry classes but I had a refresher this morning.
As I went outside to put salt on the ice that appeared overnight, I thought <
isn,t it wonderful how the salt boils the ice and turns it into water.> It
became obvious to me that salt, at some level, must also boil water.
Regards and thank you,
Harvey Opps
Another possibility is that ordinary salt or sand could be preheated (in an oven, for example) to a sufficiently high temperature and then be placed into a cavity around the pot to raise the temperature inside the pot and accelerate processes taking place in the food.
If this was ever done, use of non-preheated salt or sand could have been banned as a precaution against use of the preheated variety.
At this point, I suggest that the appropriate technical people do an experiment to see if salt or sand preheated in an oven of ancient design could do what I suggested above. Sincerely,
Robert A. Miller Manager, Materials Development TAFA Incorporated 146 Pembroke Road Concord NH 03301 USA