ensuring a more free-flowing pour of the salt. 

Before this, salt was kept in cellars  and broken into clumps or kept in bowls  

with spoons. The introduction of magnesium  carbonate revolutionized salt storage and usage. 

That's why The Morton Salt company later adopted  the slogan "When it rains it pours", meaning  

that its salt containing magnesium carbonate  would not stick together in humid weather.