Place the apricots in a large, non-reactive mixing bowl with the sugar and lemon juice. Toss to combine, and set aside to macerate for 30 minutes. 

Place the apricot mixture in a heavy, wide preserving pot, and bring to a boil over high heat. Stirring constantly, boil until the jam thickens, about 15-20 minutes. Test for doneness with this trick: spoon a bit of hot jam onto a small, chilled plate. Place it in the freezer for 1 minute. Push a fork through the jam. It should cling to the plate with a thick consistency. 

With a small ladle, pour the jam into prepared jars (see note). Seal, and process covered in boiling water for 10 minutes, starting the 10 minutes after the water in the pot has returned to a full boil. Allow the jars to cool overnight.

Store in a cool, dark place.