Note 4 — Chapter X · SODIUM CHLORIDE—BERTHOLLET'S LAWS—HYDROCHLORIC ACID
George Kamensky translation
The double salt KCl,MgCl2 is a crystallohydrate of KCl and MgCl2, and is only formed from solutions containing an excess of magnesium chloride, because water decomposes this double salt, extracting the more soluble magnesium chloride from it.