Oil of vitriol

1433. Oil of vitriol is found to grow sensibly heavier in exact proportion to the less or greater quantity of moisture it imbibes from the air. The alteration is so great, that it has been known to change its weight from three drachms to nine. Any deliquescent salt, or a strong solution of a deliquescent salt such as the carbonate of potash, commonly called oil of tartar per deliquium, may be substituted for the oil of vitriol.