On the 

 pyn-clee- 

 tririty of 

 the tour- 

 maline. 



< ol.l 



Simple me 

 i hod of 

 showing 

 the pyro- 

 Icctritity 

 of tourma- 

 line. 



the tourmaline have been already described under ELCC- 

 ruriu.iiin -,., MV| Vol. VIII. p. 456. 



t In pursuing his experiments on this curious sob* 



ject, .U Many found that the electricity developed by 

 heating / unnuline and tlie ftliceuiu ojudc ufzini:, in- 

 stead ot disappearing, a had be(-n Mi|i|n>M-d, in an abrupt 

 manner at the ordinary temperature, had only reached 

 the point or node through whieh it parsed into an op- 

 posite state by a farther reduction of temperature. By 



thangeithe tl le application of cold, therefore, to the tourmaline 

 '' and oxide of zinc, he determined that the pole which 



titcuidty*" P 088 ** 8 "! vitreous electricity when hut developed re- 

 xinuus electricity when cold.* 



It has been shown by Dr. Hrewtter, Edinburgh 

 Journal of Science, vol. i. p. 211, that the electri- 

 city of tourmaline may be exhibited in a very satis- 

 factory and simple manner by means of a thin slice 

 taken from any part of the prism, but particularly 

 when its surfaces are perpendicular to the axis of the 

 prism. The slice is then placed upon a piece of well 

 polished glass, antl the glass heated to a considerable 

 degree. About the heat of boiling water the slice will 

 adhere to the glass so firmly, that even if the glass is 

 above the tourmaline, the latter will adhere to it 

 for five or six hours. In this way slices of very 

 considerable breadth and thickness will develope as 

 much electricity as is capable of supporting their own 

 weight. 



In order to show the electrical phenomena of the 



tourmaline tourmaline to great advantage, by combining the action 

 of its two poles, Mr. Sivright fitted up a crystal so as 

 to resemble the letter C, with an opening in its round 

 side. The straight part of the letter represents the 

 crystal, and the two curved portions are pieces of sil- 

 ver wire rising out of two silver caps, one of which 

 embraces each pole of the tourmaline. If a fifth ball 

 is suspended at the opening between the ends of the 

 wires, it will vibrate in a beautiful manner in conse- 

 quence of their opposite actions. 



Sir Humphry Davy has stated, Elements nf Chemical 

 Philosophy^ vol. i. p., 130, that " when the stone is of 

 considerable size flashes of light may be seen along its 

 surface." 



2. O/i the Exigence of Puro- Electricity in various Mi- 

 nerals. 



On the ex- The subject of the pyro-electricity of minerals has 

 istence of been recently examined by Dr. Brewster, Edin/iurgk 

 pyro-elec- Journal of Science, vol. i. p. 208. The following list of 

 tricitj in pyro-electrical minerals shows the minerals in which 

 vauousmi- py ro . c lectricity has been discovered by preceding ob- 



SCIENCE. *573 



exposed to heat. He wed also a delicate needle of <*, 

 brass, the pivot of which moved upon a highly polish- 

 ed cap of garnet, and which was affected by very slight 

 degrees of electricity. 



In this way he determined the pyro-electricity of the 

 following minerals : 



To convert 



into a little 

 lectrical 

 apparatus 



server*. 



Mim-ralt. 



Tourmaline, 



Topaz, 



Axinite, 



Bardie, 



Observers. 

 Lcmery. 

 Canton. 

 Drurd. 

 Unity. 



Minerals. 

 Mesotype, 

 I? reunite, 

 Oxide of zinc 

 Sphene, 



! 



Otaervers. 



Haiiy. 



In order to determine the existence of pyro-electri- 

 city in minerals where it had little intensity, Dr. 

 Brewster employed the thin internal membrane of the 

 Arundo Phragmitts, which was cut with a sharp in- 

 strument into the smallest pieces. These minute frag- 

 ments were well dried, and the pyro-electricity of any 

 mineral was determined by its power of lifting one or 

 more of these light bodies after the mineral had been 



Scolezite.f 

 Moolite. f 

 Greenland metotype. 

 Calcareous ipar. 

 Beryl yellow. 

 Sulphate of barylu. 

 .Sulphate of strontites. 

 Carbonate of lead. 



Fluoi spar, red and blue. 



Diamond. 

 Yellow orpiment. 

 Analeime. 

 Antrthytt. 

 Quartz dauphiny. 

 I doc rate. 

 Mellite ? 

 Sulphur Native. 

 Garnet. 

 Dichroite. 



3. On the Existence of Pyro- Electricity in Artificial 

 Crystals. 



It does not appear from any of Haiiy 's writings, On the 

 that he even suspected the existence of pyro-electri- 

 city in crystals formed by aqueous solution. In sub- 

 jecting some of these to experiment, Dr. Brewster was 

 surprised to find that they possessed this property, and 

 some of them to a considerable degree. The follow- 

 ing is a list of those in which he discovered it : 





- Tartrate of potash and soda. 

 Tartaric acid. 



Oxalate of ammonia. 

 Oxymuriate of potash. 

 Sulphate of magnesia and soda. 



ammonia. 

 Iron. 



Sulphate of magnesia. 

 I'ruvsiale of potash. 

 Sugar. 



Acetate of lead. 

 Carbonate of potash. 

 Citiic acid. 

 Oxymuriate of mercury. 



Among the preceding crystals, the tartrate of potash 

 and soda, and the tartaric acid, are pyro-electrical in 

 a very considerable degree ; but the action of several 

 of the other salts is comparatively feeble. 



4. OH the Pyro-Eleclricity of the Powder of Tourmaline. 



Among the curious properties of artificial magnets, On the pjr- 

 none is more remarkable than that which is exhibited ro-leetri- 

 by cutting a piece from one of their extremities. If Cl 



the piece is taken from the north pole of the magnet, J 



. .i/. i , ~ tourmaline, 



it is itself a regular magnet, with north and south po- 

 larity. The very same property was discovered in 

 the tourmaline by Mr. Canton, who found that, if it 

 was broken into two parts when in a state of excita- 

 tion by heat, each fragment had two opposite poles. 

 Coulomb has ingeniously explained the magnetical 

 fact, by supposing that each particle of the magnet is 

 itself a magnet with opposite polarities ; and Haiiy 

 has applied the same explanation to the analogous phe- 

 nomena in the tourmaline. 



If we attempt, however, to reduce the magnet into 

 minute portions by any mechanical operation, such as 

 filing, pounding, &c. the particles of steel are found 

 to be deprived of their magnetical qualities, their co- 

 ercive power being destroyed by the vibrations or 

 concussions which are inseparable from the process 

 of comminution. Analogy would lead us to expect 

 the same result with the tourmaline ; and we have no 

 doubt that most philosophers, confiding in the force 

 of recognised analogies, would expect tnat the powder 

 or dust of pounded tourmaline would not exhibit any 

 pyro-electrical phenomena. 



In order to ascertain this point, Dr. Brewster pound - 



Our countryman Mr. Canton seems also to have discovered this point long ago. 

 f It is probable that the metotyyc of Haiiy was one or other of ilicse two minerals. 



