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I forgot to mention that I doubt that the small particle size was due to the mail-processing equipment. The equipment might break up particles into finer particles, but I don't think it would coat the newly-formed tiny particles individually.

Thanks for the information, which is so detailed and interesting. This relates to an earlier post of yours where you said that it would be significant if one could find evidence of testing dispersal equipment.

Still, the guy I am citing formerly was Deputy of the USSR biological warfare operation. He knows what he is talking about.

For purposes of discussion we must presume that neither you nor I have tried this! An experiment would seem to be in order.

Oh, yes, the "coating" - they haven't told us what it was. Early on there was speculation that it was the same stuff Saddam Hussein used, and every now and then someone with a Middle-Eastern ISP address comes in here and claims that it was or was not. We can only guess who those folks really are.

These were standard USPS envelopes purchased at the counterline. The only thing that's on the inside of the envelope is cellulose and lignan. Since these envelopes are always traditionally purchased from the lowest cost bidder, it's entirely possible that the lignan content was lower than normal - almost to the point where the paper fibers would begin pulling apart if subjected to stress. (USPS used to peddle high linen content envelopes, but that's been years ago.)

Notice that the sender wrapped each envelope in clear plastic packing tape (probably that standard stuff 3M makes). It's possible the sender knew this stuff leaked through envelopes. Maybe it had been tested earlier!

Assuming normal rate of decay in the USPS envelopes, which is probably pretty high once they are in use, the powder would have had a rough surface against which to grind as the piece moved through the system. Unless the terrorists put some other additive in the batch, the only coating available would be cellulose.

Cellulose and agar-agar are essentially the same material, with agar-agar being considered almost purely cellulose. Agar-agar is used as a fixitive in labatory activities. You add water you get jello! Add cream, you get fake ice-cream. Add some sulfur and potassium nitrate, and you get something akin to nitroglycerin - keep that in mind.

If it's just cellulose coating those particles, the investigators would have been surprised but not startled since that's one of the most common materials to be found in any laboratory (to say nothing of the insides of envelopes).

By the way, does anyone know how hard or abbrasive anthrax spores are? Are we talking something with the qualities of feldspar, or something more like diamond dust?