No, it's not a drug reference.
It is, quite simply, baking soda.
When Big Sprout was a baby, her skin was terribly sensitive. She was allergic (I think) to most brands of diapers. She would get so sore, and sometimes her rashes would get to the point she bled. It was heartbreaking, to say the least.
We finally found diapers that worked well for her, and a friend introduced us to a miraculous cream that cleared up diaper rash quickly and painlessly. The thing she liked best, though, was baking soda baths. Baking soda is something my Mom has used for both my Bro and I, as I am sure her Mom used it for her and her sister. I suppose it has been used for similar uses since baking soda was invented.
Big Sprout loved it. Soon she started requesting "the Magic Powder" for every little thing. She put it on sunburn, rashes, bruises and scrapes. As she got older, she even learned to make a paste of it to put on troublesome bug bites to take the itch away.
When we moved to live with DH, I tried giving her baking soda for her bath when she was sore, but she would never take it from me. After a few months of this, I finally realised that the reason she wouldn't take it was that it didn't look the same as "Grandma's Magic Powder". See, my Mom kept hers in this awful harvest gold Tupperware canister. Big Sprout just couldn't believe that good old Arm and Hammer was anywhere near as good as the stuff that Grandma got out of that yellow tub.
Here is where it gets good...
That year, as a gift, my Mom found a harvest gold canister just like the one at her house, filled it with baking soda, put a cute label on it that said "Grandma's Magic Powder" and gave it to Big Sprout as a gift. Mom even put a special scoop in the canister. I have never seen a child so happy over something so simple! Big Sprout would gleefully put "Magic Powder" in every bath she took. Quite often she put in too much, but she was so happy. My job was to sneak into the bathroom every night to make sure that the canister was full.
It was a sad day when Big Sprout told us she had figured out the secret of "Grandma's Powder". In time, she outgrew baths and the canister is now stored away for Little Sprout to use when she gets a little older. After all, every kid needs a little bit of "Grandma Love" of their very own.