Question 10
Fish, rice and plant leaves are heated strongly in crucibles, and the result is rubbed on white paper. What is seen, and what does it show?
The right answer is the one marked above.
Lines drawn with charcoal are obtained. The black residue is carbon, so the biological material contained carbon (C).
The purple colour belongs to the nitrogen activity: mix egg white or fish juice with excess sodium hydroxide, add a few drops of copper sulphate, and a purple colour appears — those materials contain protein, and protein contains nitrogen.