sentences:  The [H2W12O42]10− ion is known as the paratungstate B ion, as opposed to the paratungstate A ion, that has the formula [W7O24]6−, similar to the paramolybdate ion.The existence of the paratungstate A ion, could not be confirmed by NMR spectroscopy, however.Before about 1930, there has been some dispute about the exact composition of the salt, and both (NH4)10W12O41 and (NH4)6W7O24 were proposed.