<<Disclaimer: Verify this information before applying it to your situation.>>
 
According to my Merck Index, cream of tartar is also known as potassium
bitartrate or potassium hydrogen tartrate.  The chemical formula is
KHC4H4O6 (the numbers should, of course, be subscripted).  I'll try to
check on the german name later, when my husband goes home and can look it
up in his old dictionary.  It's an acid, and so will react with
baking soda to provide the gas (CO2) for the leavening. In a pinch, you
could try substituting some other acid (vinegar, sour cream, yogurt,
buttermilk).
 
Jenny Herl              |   "The world has enough for everyone's need,
[log in to unmask]         |    but not enough for everyone's greed."
University of Illinois  |
Urbana-Champaign        |    --attributed to Mahatma Ghandi (1869-1948)