The Chemistry, Properties and Tests of Precious Stones

and Electri

people of pre-historic times; later to the early Egyptians, and, at a still later date, we have recorded how Thales-the Greek philosopher, who lived about th

but also under the influence of light, heat, magnetism, chemical action, pressure, etc., and of holding or

found that some of the stones are more capable of giving and receiving charges of electricity than are others; also that some are charged throughout with one kind only, either positive or negative, whilst others have both, becoming polarised electrically, having one portion of their substance negative, the other positive. For i

e influence of heat, or is in any way connected with a rising or falling of temperature in a body, it is called "pyro-electricity," from the Greek word "pyros," fire. The phenomenon was first discovered in the tourmaline, and it is observed, speaking broad

n a silken thread from a glass rod or other non-conducting support in a similar manner to the pith ball, the tourmaline will be found to have become an excellent magnet. By testing this continually as it cools there will soon be perceived a point which is of extreme d

shaken up together in a paper or similar bag, the moderate friction of particle against particle electrifies both; one negatively, the other positively. If, then, a little of this now golden-coloured mixture is gently dusted over the surface of the tourmaline or other stone possessing electric polarity, a most interesting change is at once apparent. The red-lead separates itself from the sulphur and adheres to the negative portion of the stone, whilst t

me electric properties, however excellent some imitations may be in other respects. Further, almost all minerals lose their electricity rapidly on exposure to atmospheric influences, even to dry air; the diamond retains it some

n the application of pressure are suc

ly known as magnetite, or lodestone, has the power of attracting a magnet when swinging free, or of being attracted by a magnet, to account for which many plausible reasons have been ad

eS, Fe2S3, and is a sulphide of iron, is responsive both positively and negatively. Bismuth and antimony also are inactive, whilst almost all minerals containing even a small percentage of iron will deflect the magnetic needle, at least under the influence of heat. So that from the lodestone-the most powerfully magnetic mineral known-to those minerals

the same analytically as the gem it is supposed to represent, without completely spoiling the colour. So that the behaviour of a stone