Lime Marmalade

Since we came back from Montana, I have had a bit of a lime obsession. There was a salad there with lime zest and juice that caught my fancy. Then I started putting a slice of lime in my water. Ymm. Better than lemon. And then, double whammy, the grocery store had limes 10/$1- or 10 cents each. That did it.
I stocked up on limes. Then I had to find something to do with them. One year, I had made salted limes, but didn't like the results. I don't use that much salt in my foods and didn't find the product useful. I have grated off much of the rind of 5 limes which I froze for future use and I made some lime juice frozen cubes for later as well. Still have about 15 limes to go.
I decided that I would try some lime marmalade. Last year, my daughter made some Meyer lemon marmalade that was delicious. And Orange Marmalade has always been a favorite of mine. So with my new found love of lime, I settled on Lime Marmalade. Now to find a good recipe.
In my online and book research, I found many different approaches to marmalade. Sometimes, the qualities of the fruit affect how you will proceed. If the skin is so tough that soaking and boiling cannot soften it to mush, you cannot use the skin in any thick preparation. Only fine grating of a little bit will work. Some recipes called for paring the colored skin part, chopping fine, scraping the pithy white parts, making little bags of stuff, straining. Really, I am much too lazy for this.
I found a recipe that got me excited. Cut off the tough ends of the fruit, cut it in half lengthwise, slice thinly, soak overnight in water to cover. I am on this one. Let's follow the lead.
I sliced 10 limes very thin, there were no seeds. I put them in my container and they measured about six cups. I added 4 cups of water which covered them. I put them in the fridge and went to bed. So far, so good.
The harder part is in the morning. Simmer the fruit/juice for about an hour until the skins are soft and can easily be broken with the press of a finger. Let it cool. Measure out the water/lime mix. In small batches- 2 or 3 cups at a time, cook the marmalade with the following ingredients.
Add 1 cup of sugar for each cup of juice/pith.
Add 1/4 teaspoon baking soda in this pot- this will make it very foamy
Add 1/4 teaspoon salt in this pot.
1/2 teaspoon butter.
Over medium heat, stir the mix until the sugar has dissolved and the foam has subsided. Continue cooking with out stirring until the mix reaches 224 f degrees on a candy thermometer. Most recipes say to cook to 220 but I think it is a bit low and I have uncertainty with my equipment. Go higher if in doubt. IF there is scum or foam remaining, skim it off. For mine, it all stuck to the sides of the pot.
Ladle out the marmalade into sterile jars and water bath process.
Most of the actual canning process information can be found on line or in books. I don't want to repeat it here.
What I changed here, is that I added a little salt, butter and some baking soda. This was a synthesis of different recipes. I also increased the temperature because many people had mentioned difficulty getting the jam to set.
The first batch set up fast and very firm. So small batches seems to be the ticket. The second batch had 4 cups of juice/pulp and 4+ cups of sugar. It was a little softer, which is ok, too.
My 10 limes made about  8 cups of marmalade.
It is cooling now. I am thinking about English muffins and marmalade for lunch.