ELECTRICITY. 



461 



Kleciriciqr. 



Electricity 

 produced 



by the melt- 

 ing of re- 

 nous bo- 



|bt, 



SECT. II. Oft the Kiectricity produced by the melting of 

 Resinous Bodies. 



Mr Stephen Gray -was the first person who observed 

 that electricity was produced, when bodies merely chan- 

 ged their form. He made his experiments with black 

 and white rosin, stone pitch, shell or gum lac, bees wax, 

 and sulphur. These bodies were compounded in diffe- 

 rent ways, so as to form the substances in the following 

 Table : the first column of which contains the name of 

 thu substance, either simple or compound ; and the se- 

 cond its weight. 



All the bodies in the preceding Table, excepting Nos. 

 J8 and 19, were prepared in the following manner: 

 They were melted in the proper quantities in iron la- 

 illt-sandas soon as they were taken off the fire, they were 

 set by to cool and harden. The ladle was then placed 

 on the fire for a short time, till the substance was melt- 

 ed at its bottom and sides, and, by in verting the ladle, 

 tlit substance wns easily taken out, and liad the form of 

 nearly the section oi' a sphere, both the convex and the 

 plane surfaces being polished in cooling. 



When any of these substances were taken out of the 

 ladle, and their convex surfaces hardened, they did not 

 exhibit any electrical indications, till their temperature 

 was diminished to nearly that of a lien's egg when new- 

 ly laid. The electricity gradually increased, and when 

 they were cold, it was nearly 10 times greater than at the 

 preceding temperature. In order to preserve these bo- 

 dies in a state of attraction, he wrapped up the larger 

 ones in white flannel.or black worsted stockings; and the 

 smaller ones in white paper, and placed them all in a 

 large fir box. 



The cylinder of sulphur, Xo. 18, was formed by 

 melting the sulphur, and pouring it into a cylindrical 

 glass vessel, which had been previously heated to pre- 

 vent it from cracking. As soon as the sulphur was 

 hardened, it fell out of the glass by inverting it, from 

 having contracted during cooling, and had a surface as 

 perfectly polished as the glass itself. The large cone of 

 wan made in a similar manner, by melting the 



sulphur in a large drinking glass. Mr Gray examined 

 all the bodies 30 days after they were made, and found 

 that they attracted as vigorously as they did at first, 

 and some of them did not Jose their attraction till after 

 4 months. The cone of sulphur, No. 1 9, began to at- 

 tract about two hours after it was taken out of the glass ; 

 and the glass itself attracted likewise, but very feebly. 

 On the following day, when the sulphur was taken out 

 of the glass, its attraction was very strong, and that of 

 the glass imperceptible. The cone of sulphur was in 

 these cases placed with its base on the top of the fir 

 box, where the other electric bodies lay, and the glass 

 placed over it ; but finding this place inconvenient, 

 Mr Gray removed it to the table, between the two win- 

 dows of his chamber, and whenever the glass was taken 

 off, it attracted at as great a distance as the sulphur. 

 Afterwards the glass attracted at a less distance than 

 the sulphur. The cake of sulphur, No. 20, was laid 

 with its flat side downwards upon a table, and though 

 it had no covering of any kind upon it, the attraction 

 of this, as well as that of the other substances, always 

 varied with the weather; but the attraction of the cake 

 of sulphur was never more than one-tenth of that of 

 the cone. Mr Gray observed all these attractions, by 

 the action of the electrical bodies upon a fine white 

 thread tied to the end of a stick.* 



Experiments similar to those of Mr Gray were made 

 by M. Wilcke of Uostock, who called the electricity 

 which was in this way produced, spontaneous electricity. 

 /Kpiuus made experiments on the same subject ; but as 

 we have already given a sufficiently full account of 

 these in our History of Electricity, p. 42S, 424, it is 

 needless to repeat them hi this place. 



Mr Henley repeated the experiments of Mr Gray, 

 and obtained nearly similar results. He discovered 

 that electricity was exhibited by chocolate, when it was 

 cooled in the tin pans into w Inch it is received. At 

 first the electricity is strong, and it is retained for some 

 time after it is taken out of the pans, though it soon 

 loses it by handling. When it is again melted and al- 

 lowed to cool, the electrical virtue is restored, but not 

 to its former strength. After the third or fourth melt- 

 ing, however, the electricity is extremely weak. When 

 the chocolate is mixed with a little olive oil before it is 

 poured out of the pan, it then becomes strongly electrical. 



These experiments of Mr Henley were repeated and 

 verified, in 1784, by M. Pabst, and in 1787 by M. Lip- 

 hardt of Konigsberg. The last of these writers being 

 at one time occupied in preparing chocolate, placed some 

 cakes upon one another, and having held a bundle of 

 silk threads within two inches of them, they were at- 

 tracted with great velocity, and adhered to .the cakes. 

 M. Liphardt also found that talc melted and cooled 

 gave electrical symptoms. Thinking that electricity 

 could not be produced without friction of some kind, 

 M. Liphardt took four ounces of warm and liquid 

 chocolate, and having placed them upon_an iron plate, 

 he brought near the silk threads, but observed no indi- 

 cations of electricity. He then put the mass into 

 kliapc, and having struck it well against a flat surface, 

 as is the custom in extending the chocolate, he took it 

 warm out of the shape, and found it to be electrical. 



M. Liphardt made also some experiments on the' 

 electrical effects produced by a sudden blow. He let 

 fall a piece of sealing-wax, from the height of 8 inches, 

 upon a table, and repeated this from 10 to 20 times., 

 when it exhibited marks of electricity. Gum copal 



Descriptive 

 Electricitf. 



Experi- 

 ments of 

 Wilcke an* 



Henley's 



experiments 

 on the 

 electricity 

 of melted 

 chocolate. 



Experi- 

 ments of 

 Liphardt 

 on choco- 

 late. 



See Pkil Traiu. 1737, roL xxxni. p. 385, 



