20 On Light. 
Sulphate of barytes gives a bright green light, 
Carbonate, Do. less brilliant. 
Acetate of potash, Brilliant green light, 
Succinic acid, Do. more durable. 
Loaf sugar, Do. 
Selenite, — Do. but transient. 
Rock-crystal, Light red, and then white. 
Quartz, Dull white light. 
Borax, Faint green light. 
Boracic acid, Bright green light. 
Mr. Skrimshire has given an extensive catalogue of such sub- 
stances in Nicholson’s Journal, 8vo, vols. 15, 16, and 19. He shows 
that Canton’s pyrophorus yields more light by this treatment than 
any other body; but that almost every native mineral, except 
metallié ores an d metals, becomes more or less luminous after the 
electric explosion. A. slate from Colly Weston, Northampton- 
shire, which effervesced with acids, gives a beautiful effect. When 
the explosion of a jar is taken above the centre of a piece some 
inches square, not only the part above the discharging rods is lu- 
minous, but the surface of the plate appears bespangled with very 
minute brilliant points to some distance from its centre ; and 
when the points of the dischargers rest upon_the surface of the 
slate, these minute spangles are detached, and scattered about 
the t ble in a luminous state. 
5. Light emitted during chemical changes independent of heat, 
or in which no perceptible heat is developed. The substances 
from which such light is emitted, are principally the following : 
Marine animals, both in a living state and when deprived of 
life. As instances of the first may be mentioned the shell-fish 
called Pholas, the Medusa phosphorea, and various other Mol- 
lusca. When deprived of life, marine fishes, in general, seem to 
abound with this kind of light. The flesh of quadrupeds also 
evolves light. In the class of insects, are many which emit light 
very copiously, particularly several species of Fulgora, or lantern- 
fiv; and of Lampyris, or glow-worm ; also the Scolopendra elec- 
trica, and a species of crab called Cancer fulgens. Rotten wood 
is well known to evolve light copiously, as well as peat-earth. 
Dr. Hulme, iu aa elaborate dissertation on this light, published 
in the Piil. Trans. for 1790, establishes the following important 
propositions : 
1. The quantity of light emitted by dead animal substances, 
is not in proportion to the degree of putrefaction in them, as is 
commonly supposed ; but, on the contrary, the greater the pu- 
trescence, the less light i is evolved, It would seem, that this ele- 
ment, endowed with pre-eminent elasticity, is the first to escape 
from ‘the condensed state of combination in which it had been 
imprisoned 
