Follow steps 1 through 4 of Canning Instructions, using four pint-size jars.
Pit and coarsely chop or mash apricots; you should have 3 cups. Coarsely mash raspberries; you should have 3 cups.
In an 8- to 10-quart pan, mix 1/4 cup of the sugar with the pectin. Add apricots, raspberries, lemon juice, and butter (if using); stir until pectin is well blended. Bring to a rolling boil over high heat, stirring often. Stir in remaining 4 1/4 cups sugar; when mixture resumes boiling, stir for exactly 1 minute. Remove from heat immediately.
Skim and discard any foam from jam. Stir often for 5 minutes to distribute fruit. Follow steps 5 through 11 of Canning Instructions, leaving 1/4 inch of headspace and processing jars for 5 minutes (see Notes).
Sunset's Canning Tips:
Add butter to jams and jellies to prevent foam from forming during cooking. If you omit the butter, skim off the foam before ladling jam or jelly into jars. The recipe will yield about 1/4 cup less.
Measure all the sugar into a bowl before beginning the recipe. Many canning recipes call for a large volume of sugar to be added when a mixture is already boiling; measuring ahead simplifies this step and prevents mistakes.
Use a ruler to measure volume. Some recipes call for a mixture to be reduced by a certain amount. To ascertain this easily, insert a clean, wood ruler into the pan before cooking and measure how far up the mixture comes. Then cook as directed until it has reduced by the percentage specified. For example, if uncooked mixture measures 4 inches in pan and recipe says to reduce by half, cook it down to 2 inches.