In a small microwavable bowl, sprinkle the gelatin over 3 tablespoons of the water and let stand until softened.
In a medium saucepan, combine 1 1/2 cups of the sugar with the corn syrup and the remaining 3 tablespoons of water. Bring to a boil, stirring, until the sugar is dissolved. Keep warm.
Meanwhile, in a standing electric mixer fitted with a whisk, beat the egg whites with the lemon juice and salt until soft peaks form. Gradually add the remaining 1/2 cup of sugar, beating at high speed until stiff and glossy. With the mixer at medium speed, slowly and carefully add the hot sugar syrup in a thin stream. When all of the syrup has been added, beat the meringue at medium-high speed until slightly cooled, about 5 minutes. Microwave the gelatin until melted, about 15 seconds. With the mixer on, beat the melted gelatin into the meringue. Use right away.