Because it contains an alkaline substance called Morphia.

To Clean Utensils that have Contained Fat.-Analkaline substance such as washing soda is effective in cleaning utensils that have held fat.

The alkaline substances used in this process of scouring demand some notice.

The salts and acids of fruits are broken up in the stomach and help to form alkaline substances.

The addition of further alkaline substances is unnecessary and only succeeds in selling soap because the average person is ignorant of the nature of soap.