You can heat it with an electric plate, but you will be limited to lower temperatures. You can also use a portable gas stove, like the ones used for camping. Example:
That will give you higher temperatures than electric plates, but still lower than a good Bunsen or Meker–Fisher burner.
The alchemists and chymists used wood and charcoal furnaces to heat their glass vessels. They did not have borosilicate glass, so they had to avoid giving their glassware too sudden a thermal shock or they would crack, so what they would do is heat glass vessels inside "baths": water baths for lower temperatures and sand baths for higher temperatures. For subjecting glass vessels to even higher temperatures what they did was to coat them with refractory "lutes" (usually mixtures of clays and sand) and allowing them to dry into a "shell" that surrounded the glass vessel. That would allow them to expose the glass to higher heats that would normally not be possible due to the glass softening and deforming (the refractory "shell" would also protect the glass from direct exposure to increasing heat, thus lowering the thermal shock.)
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