Years have gone by, and I've recently come up with something much better. OK, now is the time to confess that the title of this instructable is a bit of an exaggeration; this recipe won't actually cure the common cold (or the flu) but it will make you feel a whole lot better for a while. Don't eat these! They are bath melts, designed to dramatically enhance the natural relaxing power of hot water. Make them in anticipation of the bad days or whip up a batch for a sick acquaintance -- you will get a friend for life.
Step 1: Ingredients and materials
1/3 cup baking soda
7 1/2 tsp citric acid
1 tbsp cornstarch
2 oz mango butter (approx 1/3 cup)
1/8 tsp peppermint essential oil
1/4 tsp eucalyptus essential oil
1/8 tsp lavender essential oil
Scented bath salts (optional -- scent the salt with the above essential oil)
Double boiler (or small metal pot which can sit in a larger pot of simmering water)
Ice cube tray or small candy molds
Glass jar with airtight seal or plastic ziplock bags.
Notes on ingredients:
Citric acid can be found in the kosher section of supermarkets under the name "sour salt." In Brooklyn, New York, Sahadi's on Atlantic Avenue carries for $4 a pound it but they call it "lemon salt." Apparently it can also be found at brewers supplies stores. I've also seen it in regular supermarkets (if you call Garden of Eden regular) with their other spices and even at a cake supply store (but it costs MUCH more when they sell it in those tiny spice jars). If all else fails, buy a large stash online and make borsh, bath bombs and dishwashing detergent as well as alka selzer. You'll find it at other places too, but this site carries it.
Mango butter is an oil which is solid at room temperature. It is extracted from mango pits. It is softer than cocoa butter and its smell is milder than either cocoa or shea butter. It also works better for bath melts like this one than either of those butters. Besides the smell issue cocoa is too hard, and shea, for some reason, always makes the citric acid and soda combination fizz up prematurely. Since mango butter is fairly expensive I thought I might be able to extract some butter from the mangos I eat -- and failed miserably. I tried dunking the seed (after removing the tough hull) in the bath and scratching it, I tried grinding it up and pressing it in a garlic press, but I only got a dirty bathtub and a dark brown bitter liquid, not the creamy pale yellow butter to be used in cosmetics. Apparently only 15% of the seed is butter, so I would need many more than the handful of seeds I used, and industrial means of extraction to get at it. I've never found it locally, but plenty of online suppliers (including the citric acid vendor above) will be happy to ship it to you wherever you live.
Essential oils can be found in health food stores (even though you are not supposed to eat them!), and there are many online sources too. Essential oils are very concentrated and they need to be handled with caution. Use in a well ventilated area or risk getting a headache. Always dilute with a carrier oil (otherwise known as regular oil, the type you cook with) before putting on your skin. Essential oils are volatile, and they will quickly loose their fragrance when they are heated. This is why they are always added to recipes after the mixture has cooled.