438 
SECOND REPORT- 1832 . 
presents another instance. If the crystals of this salt, rectan¬ 
gular four-sided prisms, be taken between the fingers and then 
laid on bibulous paper, they become opaque at the point which 
has been in contact with the fingers, and the opacity spreads 
over the whole crystal, which by a slight touch falls to a white 
deliquescent powder*. A third example is the mellate of am¬ 
monia. This salt, according to Wohler, crystallizes in two forms, 
one of which immediately on being taken from the mother liquor 
becomes opaque and pulverulent either in the air or in vacuo , 
and without loss of water f. 
All these phenomena are probably dependent on the same 
principle which gives rise to the more distinct isomeric modifi¬ 
cations of the tartaric and paratartaric acids. They are ana¬ 
logous, in the facility with which the change is effected, to the 
phenomena observed by Mitscherlich in the crystals of the 
sulphate of nickel and seleniate of zinc. If the prismatic 
crystals of the latter be laid on paper and exposed to the rays 
of the sun, in a few moments they become opaque, and are 
found when broken to be made up of minute octohaedrons with 
square bases,—the other form of which the salt is susceptible. 
The similar crystals of sulphate of zinc undergo a like change, 
but more slowly. 
The nitrites and vanadiates are sometimes yellow and some- 
timet colourless, and from one and the same solution may oc¬ 
casionally be obtained colourless and beautifully reddish cry¬ 
stals of the sulphate of protoxide of manganese identical in com¬ 
position. Both classes of phenomena, and many others of a 
similar kind, may probably find their proper explanation in 
isomerism. 
II. List of Metameric Bodies. 
2 0 J. 
{ Cyanuricacid-f (Cy+ 20 + H) 1 2 atoms of the former 
Hydrous cyanic acid Cy+Hj =3 atoms of the latter. 
Naphthaline 5 C + 2 H, density 1 
of vapour ”4*528. ^ .*. 3 vol. naphthaline = 
Paranaphthaline 5 C + 2 H, f 2 vol. paranaphthaline. 
density of vapour = 6*741.., 
* This is an observation of Hermann,—Poggendorf ’s Annalen, xv. 4S0. 
f Berzelius, Traite de Chim. vi. p. 607. 
X It is difficult to say whether these two are rightly placed in this group, as 
we have no means of determining how many volumes of paranaphthaline vapour 
constitute an atom. According to Dumas, four volumes of naphthaline vapour 
constitute an atom. We are indebted to Dumas for the discovery of paranaphtha¬ 
line, and I have followed him {Ann. de Chim. 1. 183,) in stating the composition 
