Is lithium carbonate at all hygroscopic? If so, then anhydrous 
lithium carbonate (or  less than maximally hydrated Li2CO3) will pull 
water out of the air, creating Li2CO3 . nH2O, of undetermined 
molecular weight, since the "n" -- the hydration state -- is unknown. 
This is also true for Na/Na2PO4, K/K2PO4 and suchlike salts. Meaning 
that when buying these compounds for buffers or medicines (e.g.), 
it's best to buy the maximally hydrated version, otherwise the amount 
weighed out will be incorrect, too low, because of the unknown amount 
of water taken up by the salt.

Phil

>I've seen bottles of lithium carbonate with the note on them that their
>lithium carbonate has no definite molecular weight. Presumably these batches
>were prepared from lithium that had been depleted of lithium 6 for use in
>making hydrogen bombs, and thus were highly enriched in lithium 7. I suppose
>that this anomaly is taken into account in preparing medicinal lithium
>carbonate, since the dosage range (therapeutic index) of lithium carbonate is
>very narrow.
>
>Bob Richmond
>Samurai Pathologist
>Knoxville TN

-- 
Philip Oshel
Supervisor, AMFSC and BBPIC microscopy facilities
Department of Animal Sciences
University of Wisconsin
1675 Observatory Drive
Madison,  WI  53706 - 1284
voice: (608) 263-4162
fax: (608) 262-5157 (dept. fax)