Photophore

—A form of endoscope em- Pickle.—To steep in an acid bath, for the ploying a small incandescent lamp for expurpose of removing impurities; as, in the amning the internal cavities of the human following: ody. 1. In boiler making, the plates are steeped on edge for a period of six hours, in racks Photosphere.—The luminous envelope of within a wooden bath, containing a 5% incandescent matter surrounding the sun. solution of hydrochloric acid in fresh water. ‘This loosens the mill scale, which is removed by the aid of wire brooms, mechanical brushes and a plen- Photo-telegraphy.— Telegraphic transtiful supply of water. The cleaned plates are mi ion by means of light, as with a helio immersed in an alkaline bath of weak quicklime and water, to neutralize remaining acid, and graph or a photophone. finally washed in fresh water. 2. In iron founding, the castings are placed on Photo-voltaic Effect.—A change in the racks, and have a 25% solution of sulphuric acid poured over them, by means of a ladle, the acid electric resistance of a substance, especibeing collected and used over again. After stand ally of selenium,.when exposed to light. ing to drip ail night, the castings are washed down with a hose and brooms, remaining sand being removed by wire brushes and old files. A better Physical.—Relating to nature and the method is to steep for two or three hours in a operation of natural law. wooden vat containing ten per cent solution of hydrofluoric acid, which attacks scale and sand, but not iron. A vat may be used three or four ' Physical Change.—Any change occurring times with the same acid. in matter without altering its chemical Pickling Solution.—1. In electroplating, constitution, as distinguished from chemical change. an acid solution for cleansing the surface of metallic objects preparatory to plating; Physical Law.—A law according to which | the pickle. a constant relation exists between certain 2. A solution of dilute sulphuric acid for physical quantities; a law of physical immersing steel and iron to remove scale phenomena; a natural taw. and oxide before galvanizing.