All fats and oils are compounds of certain fatty acids combined with glycerine. Glycerine is easily separated from this combination by strong alkalis, and thus soaps are made. The glycerine is a by-product in many soap factories, but it is not evident in home-made soap, being thrown away with any waste water, or, perhaps, left in the soft soap. The various fats are composed of different kinds of fatty acids, so we have varieties of soap made from them.

Rosin acts like fatty acids, for it is able to combine with alkali to make rosin soap. This is good for rough work, but it is apt to separate in hot water, setting free the rosin acids, which may settle upon the fabric being washed, giving it the odor of rosin or causing it to become yellow. It is very objectionable when the clothes come to be ironed. This rosin also makes fabrics likely to take up dust. If the clothes are well rinsed, the amount of rosin soap in ordinary yellow soap gives no trouble.

I have often been asked for a recipe for home-made soap, and, too, I have had many students write me of their success in this process. Many housekeepers keep and clarify the fats from food. Soap may easily be made from this, as follows:

Take a pound can of lye (Babbitt's potash is good) and dissolve it in three pints of cold water. It will become quite hot as it dissolves, and care must be taken in adding the lye to the water, as it is apt to spatter, and is likely to irritate the hands.

Have ready five pounds of clean fat, which has been melted and strained through cheese-cloth to remove all specks of brown. When the lye is cool, pour it slowly on the grease, stirring it with a stick until the two mix, and the liquid becomes about as thick as honey. Too long stirring may cause the ingredients to separate.

Mould the soap in agate or wooden trays. If a wooden box is used, it should be lined with several thicknesses of wrapping paper. The layer next the soap should be oiled. The soap should harden in a moderately warm place, and then may be cut into cakes. This is the so-called "cold process" soap. It will not be suitable for fine work but improves with age.

Several students have described to me how they remembered seeing soap made at home from alkali obtained by leaching wood ashes. The ashes were put into a large box pierced with holes, the box placed over the soap kettle, and hot water was poured upon the top. This alkali would make soft soap, which would be stored in barrels. If hard soap were desired, salt was added to some of the soft soap.

A reaction takes place by which some of the sodium in the salt is combined with the fatty acids, sufficient hard soap being formed to harden the mass. Nowadays, even when we buy "potash" we are quite sure to find that we can make hard soap, for it almost always is chiefly soda (caustic soap).

Washing "soda has a great many uses, and I am frequently reminded of new ones by our students-. I am told how excellent it is to put a little in water and boil this in the cooking dishes on which food has hardened or burned. Another describes how she cleans silver by boiling it with a little soda, then rinsing it in very hot water and drying quickly and thoroughly. The wife of a dairy farmer assures me that she could never get her creamery cans suitably clean without plenty of sal soda, which quickly removes the butter fat. When we use it in laundry work, however, we must remember that, like other solids, when it dissolves, a saturated solution forms around each piece, and this strong solution may injure anything on which the pieces rest. Therefore the crystals should always be dissolved, and the solution diluted as much as may seem necessary.