I have 2 solids in a tube. If i start heating the recipient, will the temperature remain the same at the melting point temperature of the substance with the highest melting point?
The lowest melting point substance will being to melt first and maintain the test tube at a constant temperature until its completely melted and then the same thing will happen with the highest melting point substance.
Note that to observe constant temperature you need quite large amount of substance. To make things more complicated a lot depends on whether the second substance doesn't dissolve in the first one.