1869.] 



with the Great Induction Coil. 



69 



spark in a vertical line and in considerable quantities, the greater part of 

 the light is obscured, and the whole form of the flaming spark presents the 

 appearance of a black cloud with a line of brightly ignited particles frin- 

 ging the lower parts. If the charcoal is dusted through in small quantities, 

 each particle becomes ignited, like charcoal blown into a hydrogen-flame. 



When the flaming spark is directed on to a glass plate upon which a 

 little solution of lithium chloride is placed, the latter colours the flame 

 upwards to the height of 3 or 4 inches in the most beautiful manner ; and 

 if the point of the discharge is tipped with paper or sponge moistened 

 with a little solution of sodium chloride, the two colours (the yellow from 

 the salt and the crimson from the lithium) meet each other, a neutral 

 point being found about halfway, thus illustrating apparently the dual cha- 

 racter of electricity, and that + passes to — electricity, and vice versd. 



The flaming spark can be obtained in perfectly dry air. 



Whilst passing through common air, if blown against a sheet of damp 

 litmus-paper, the latter is rapidly changed red. In order to ascertain 

 whether the acid product was nitric acid, the flaming spark (9 or 10 inches 

 in length) was passed through a tube connected by a cork and bent tube 

 with a bottle containing distilled water, from which another tube passed to 

 the air-pump ; on drawing the air slowly over the spark, and passing the 

 former into the bottle, nitric acid was obtained in large quantities — so much 

 so that it could be detected by the smell and taste as well as by the ordinary 

 tests. The popular notion that nitric acid is always produced during a 

 thunder-storm would therefore appear to be correct. To determine the 

 effect of a cooling surface on the flaming spark, a hole one inch and a half 

 in diameter was bored through a thick block of Wenham-lake ice, and the 

 spark passed through the air in the tube of ice ; no change took place, and 

 the spark was still a flaming one. 



