CHEMISTRY (1K ZX81)
by S O'Duyer
from ZX Computing (June/July 1984), page 39

This program calculates the percentage composition by mass for a given formula. For instance, NaCl (common salt) works out to be 39.3% sodium and 60.7% chlorine. The user inputs the symbol of the element or compound and its relative atomic mass (which will have to be looked up in a chemistry text book). Three common compounds are stored for instant use by the computer but if you have 16K and the time, all the other information could be stored.