14 Observations on Naphthaline. 
long neck ; in the ypper part of which erystals will be formed, 
and deposited during the boiling. 
If exposed to a degree of heat not more than sufficient to melt 
it under a bell glass, the vapour that rises from it crystallizes 
before it reaches the surface of the glass, and flies about the in- 
terior with exactly the appearance of a shower of minute parti- 
cles of snow- 
If a piece of cotton twine be coiled up like the wick of a can- 
dle, and after having been dipped in this substance while melted 
be set on fire for a second or two, and then blown out, the va- 
pour will soon begin to crystallize round the wick in very distinct 
thin transparent lamine. 
This experiment affords one mark of distinction between this 
substance and benzoic acid, and also between it and camphor : 
for, under similar circumstances, benzoic acid crystallizes in aci- 
cular crystals, which are often grouped in a stelliform manner ; 
and camphor crystallizes, or is rather congealed, in globular 
particles having a stalagmitic appearance. 
The most usual crystalline form of this substance is a rhombic 
plate, of which the greater angle appears to be from 100° to 
105°: crystals at least- of that form I have repeatedly obtained 
from its solutions in water, in alcohol, in acetic acid, in the yel- 
low oil described in the last section ; and lastly, by melting and 
very slowly cooling the substance itself. Sometimes several of 
these plates are variously grouped together ; sometimes a single 
plate intersects another plate at nearly nght angles, so that in 
some points of view the compound crystal appears simply cruci- 
form. The only distinct modifications I have observed of the 
common form are a rhomboidal plate, which is very nearly rect- 
angular; and an hexagonal plate: the latter variety may be easily 
traced from the rhombic plate by the incomplete development of 
the smaller angles of the usual rhomb. 
The following process has been found most successful in il- 
lustrating the crystallization of this substance : 
If 25 grains of it be dissolved by the assistance of heat in half 
a fluid ounce of alcohol, and the solution be cooled slowly in a 
glass matrass, it will begin to crystallize when nearly cool; and 
the matrass being placed between the eye aad a tolerably strong 
light, numerous transparent rhombic crystals will be visible; some 
of them reflecting from their whole surface a green colour; others, 
a blue; or a red; or some other of the prismatic colours. 
With respect to the elementary constitution of this substance 
I am not enabled to give any satisfactory information; but it is 
evident that it contains a very great proportion of carbon, A 
small quantity of it was passed in the state of vapour through 
peroxide of copper heated to reduess, and the only gaseous pro- 
duct 
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