The corrosive effect of sodium chloride on the volcanic rock trachyte is more severe than the corrosion of sandstone, even though in sodium sulfate it is trachyte which is the more resistant of the two. Apparently, this is due to the chloride ions attacking the feldspars. It must be realized in this connection that the crystallization test as commonly performed using sodium sulfate solutions need not always yield a complete information about the resistance of the stone under study to the effects of water-soluble salts.