Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

Hardness in Water.

—Water that holds no mineral matter in solution is “soft water” and when soap is added will readily form a lather. The presence of lime or magnesia is commonly the cause of “hardness” in water. Either of these minerals, when present form an insoluble curd when the soap is added to the water and the soap will not form a lather until enough soap has been added to unite with the mineral matter present. The hardening agents are usually in the form of bicarbonates and sulphates. All soap used in neutralizing the hardening agents is wasted, because a lather will not form until all of the hardening materials are neutralized. It is evident that the softening of water for domestic purposes is beneficial, both because of the less amount of soap required and because of the absence of the curd.

Hardness in water may occur in two forms—as temporary hardness or as permanent hardness. When bicarbonate predominates as the hardening agent, the water is said to be temporarily hard because, when heated to boiling, the bicarbonate is precipitated and the water is thus softened. When softening of such water is to be done on a large scale, chemical treatment is more satisfactory. Water containing bicarbonate of lime may be softened by adding a pound of lime to 1000 gallons or 1 pound of lime to 165 cubic feet of the water. This quantity of lime is sufficient to remove 10 grains of the bicarbonate to the gallon.

When the mineral matter is in the form of sulphates, mainly sulphate of lime or magnesia, the water is said to be permanently hard, because boiling will not soften it. Such water may be softened by adding soda ash or impure carbonate of soda. One pound to 1¼ pounds of “washing soda” to each 1000 gallons of water will render such water soft; by its action the sulphate of lime is precipitated and settles to the bottom of the container; the water may then be siphoned off leaving the precipitate in the bottom.

Iron in Water.

—Water containing iron is found in many wells and springs. While iron is not harmful, it is objectionable to taste and stains most things with which it is long in contact. It may be precipitated with lime and removed as the sulphate of magnesia described in the preceding paragraph.

Water Softening with Hydrated Silicates.

—By W. L. Stockham, assistant chemist, North Dakota Experiment Station.

“The use of chemicals in softening water requires the mechanical removal of the separated materials by skimming, settling or filtering and it is difficult to determine just how much chemical to add. A new process for softening water, and one that has awakened great interest because of its efficiency, employs hydrated silicates of aluminum or iron combined with soluble bases. This process softens water from practically any condition or hardness.

“The form of apparatus in use varies from a portable jar, with an inlet at the top and an outlet at the bottom, to the more complex tanks for industrial and domestic purposes. A plant for domestic use might consist of a 20-gallon tank for containing the softening material and a second tank in which is prepared the salt solution for reactivating the softener. The two tanks with their valves and connections constitute the apparatus. The softener, supported by a porous plate, sieve, or layer of gravel, completely fills the first tank and the water to be treated passes through the interspaces between the granules. In some plants the water passes through a layer of marble chips before coming into contact with the softener. The apparatus may be attached temporarily to the faucet or connected permanently with the water system. A gravity system may be employed where the water pressure is lacking.