1. Manipulations

1.    Manipulations. Under this heading will be found a brief description of the various methods of chemical manipulation, constantly employed in this work. This is deemed especially necessary, as many, if not all, of the processes described, depend greatly on careful and skillful manipulation in the preparation as well as in the combination of the necessary ingredients. (See No. 3830.)

2. Annealing

2.    Annealing. The process by which glass is rendered less frangible, and metals, which have become brittle, again rendered tough and malleable. Glass vessels, and other articles of glass, are annealed by being placed in an oven or apartment near the furnaces at which they are formed, called the "leer," where they are allowed to cool slowly, the process being prolonged according to their bulk. Steel, iron, and other metals, are annealed by heating them and allowing them to cool slowly on the hearth of the furnace, or any other suitable place, unexposed, to the cold.

3. Bath

3.    Bath. In cases where an equable heat has to be sustained at, or not to exceed, a certain fixed degree, it is evident that an open fire or flame would be too variable for the purpose. To obviate this difficulty, the vessel to be heated is immersed or imbedded, to a convenient depth, in another vessel containing water, oil, saline solution, sand, metal, etc., as circumstances require, to which the heat is applied and whose temperature can be regulated, if necessary, by the use of a thermometer. Steam is also applied to this purpose; but, of course, requires special apparatus. The baths most commonly used are the water bath and the sand bath.

4. Sand Bath

4.    Sand Bath. An iron or copper vessel should be employed for this purpose. Sufficient sea or river sand, previously washed clean and dried, must be put in to cover the bottom completely. The vessel to be acted on is then introduced, and the intervening space around it filled up to the desired height with sand, and the whole placed over a furnace. The object of the sand is to cut off direct communication with the fire and produce a gradual and equable heat.

5. Water Bath, or Bain-Marie

5. Water Bath, or Bain-Marie. This arrangement is used where the heat required is not over 212° Fah., and consists of one vessel within another, secured so that they cannot come in contact at any point below the level of the water which has been introduced to fill up the space between them. A double glue-pot is a water bath.

As the temperature of water cannot be increased, in an open vessel, above its boiling point, 212°, a vessel immersed in it can never be heated above that point; and, by keeping the water boiling, this degree can be steadily sustained. Where other degrees of heat are requisite, the following table, showing the boding points of different substances and saturated solutions, will serve as a guide. A still higher degree of heat may be reached by using, with appropriate vessels, metals whose melting point is known. (See Index for Melting Point of Metals.)