The effect of sodium hydroxide and sodium sulphide on the snapping strength of egg shells

Synopsis The snapping strength of egg shells was studied before and after treatment with either water, sodium hydroxide solution or sodium sulphide solution. It was found that water decreased the strength slightly, but the other solutions gave a steady fall in strength with increasing time of treatment. The fall in strength was significantly correlated with the fall in nitrogen content, but for a given nitrogen content, the shells were weaker if treated with sodium hydroxide solution. Studies of thin sections with polarised light showed that sodium hydroxide solutions attacked the calcite crystals, whereas sodium sulphide solutions did not. Thus the treatment with sodium sulphide solution appears to weaken the shell by removing nitrogenous compounds, while sodium hydroxide solution weakens the shell even more because, in addition to removing nitrogenous compounds, it also attacks the crystals.