I agree with Bruce M's follow up. The easiest way is to remove the sash from the frame, place it on a workbench and use a heat gun to soften the paint to be scraped off with a stiff blade putty knife. I've found that heat guns with dual heat settings (500/1000 watts) work best, using the lower heat setting around the moulded corners and close to the glass and the high setting on larger flat surfaces. Use the heat gun (or propane torch) only on the sash once removed from the frame.
While a heat source on the flat large surface of a frame might be ok with extreme caution and attention as to where the heat is directed, never use heat toward corners or wood joints. Dust over the years accumulates in cracks and is easily ignited by even a modest amount of heat. It can smolder undetected for sometime before breaking out in flame.
I speak from experience. I was removing paint from windows, had finished paint removal from one window and was working on an adjacent window when a whisp of smoke from the just finished window caught my attention. I quickly removed the sash and found a silver dollar size hole had burned in the track in which the window slides up and down---and I thought I was being careful. Two weeks later a home in another neighborhood burned down when the owner was doing the same job.