Description—Purified Camphor forms a colourless crystalline, translucent mass, traversed by numerous fissures, so that notwithstanding a certain toughness, a mass can readily be broken by repeated blows. By spontaneous and extremely slow evaporation at ordinary temperatures, camphor sublimes in lustrous hexagonal plates or prisms, having but little hardness. If triturated in a mortar, camphor adheres to the pestle, so that it cannot be powdered per se. But if moistened with spirit of wine, ether, chloroform, methylic alcohol, glycerin, or an essential or fatty oil, pulverization is effected without difficulty. By keeping a short time, the powder acquires a crystalline form. With an equal weight of sugar, camphor may also be easily powdered.
Camphor melts at 175° C., boils at 204°, and volatilizes somewhat rapidly even at ordinary temperatures. To this latter property, combined with slight solubility, must be attributed the curious rotatory motion which small lumps of camphor (as well as barium butyrate, stannic bromide, chloral hydrate, and a few other substances) exhibit when thrown on to water.
The solubility of camphor in water is very small, 1300 parts dissolving about one; but even this small quantity is partially separated on addition of some alkaline or earthy salt, as sulphate of magnesium. Alcohols, ethers, chloroform, carbon bisulphide, volatile and fixed oils and liquid hydrocarbons, dissolve camphor abundantly.
The sp. gr. of camphor at 0° C. and up to 6° is the same as that of water; yet at a somewhat higher temperature, camphor expands more quickly, so that at 10° to 12° C. its sp. gr. is only 0·992.
In concentrated solution or in a state of fusion, camphor turns the plane of polarization strongly to the right. Officinal solution of camphor (Spiritus Camphoræ) is too weak, and does not deviate the ray of light to a considerable amount.[1904] Crystals of camphor are devoid of rotatory power.
The taste and odour of camphor are sui generis, or at least are common only to a group of nearly allied substances. Camphor is not altered by exposure to air or light. It burns easily, affording a brilliant smoky flame.
Chemical Composition—Camphor, C₁₀H₁₆O, by treatment with various reagents, yields a number of interesting products: thus when repeatedly distilled with chloride of zinc or anhydrous phosphoric acid, it is converted into Cymene or Cymol, C₁₀H₁₄, a body contained in many essential oils, or obtainable therefrom.
Camphor, and also camphor oil, when subjected to powerful oxidizing agents, absorbs oxygen, passing gradually into crystallized Camphoric Acid, C₁₀H₁₆O₄ or C₈H₁₄(COOH)₂, water and carbonic acid being at the same time eliminated. Many essential oils, resins and gum-resins likewise yield these acids when similarly treated.
By means of less energetic oxidizers, camphor may be converted into Oxy-Camphor, C₁₀H₁₆O₂, still retaining its original odour and taste (Wheeler, 1868).
Commerce—Two kinds of crude camphor are known in the English market, namely: