On Dimorphism of Arsenic, Antimony and Zinc. 191 
In making these observations on a single process of Dr. Mohr, 
I wish at the same time to bear testimony as to the candor with 
which he has given the results of his experimental trials. The 
proposal of a mode of rae ope such as that of Mr. Walker is a 
new proof how much it is to be regretted that any chemist 
should offer a new mode of analysis, ‘without having first econ- 
pore it by the analysis of one or more specimens of substance 
known composition. In this way MM. Glénard and Guil- 
faaninds hav recently proposed* a method of estimating the qui- 
nine in barks. It has been however shown} that not “only the 
presence of cinchonine destroyed the accuracy of these results, 
but that owing to a mistake of the authors as to the reaction 
of the sulphates of quinine upon tincture of logwood, the 
cess when performed with pure quinine gave only one-half the 
true result. 
In connection with the foregoing observations on zinc I may 
remark that an error has crept into the description of zinc reac- 
tions in Gmelin’s Handbook. It is there stated that zine salts 
- preciptates with ferrocyanid and ferridcyanid of potassium, 
of which are soluble in chlorhydric acid.t As respects the 
petbiiants with ferrocyanid, this is certainly erroneous, the pre- 
cipitate does not redissolve in that acid. 
Philadelphia, Dec. 28, 1860. 
Art. XVI.—On the eae ee of Arsenic, Antimony and Zine ; 
by Jostan P. Cooks, JR. 
THE rhombohedral forms of arsenic, antimony and zinc are 
well known. Those of arsenic and antimony have been ve 
mined by several ohatiens and that of zine first observ 
Noggerath,|| on a furnace product from the smelting works of 
the Vieille Montaigne Zinc Co., near Aix la Chapelle, was sub- 
sequently redetermined on the same specimen by Gustay 
It is the object of the present paper to show that these elements 
may also crystallize in regular octahedrons and therefore that 
they are dimorphous. Supposed monometric crystals both 
arsenic and zine have been previously described but since these 
observations have been discredited, the author has thought it 
best to publish his results. 
rsenic.—in the “ Journal fiir praktische Chemo,” vol. xxii, 
344, 1841, Elsner describes, as crystals of arse c, octahedrons, 
* Rep. de Chimie Appliquée, 1859, p. 131. Idem, pias Ft 
t Handbook, vol. v, ag Carendie albtiot. : 
§ description of erystal of rhombohedral arsenic, in Proceedings of Amori 
can Academ and Sciences, vol. iii, 86. . .. 
| Popgeadoett Aunslen, vol, nents 323 q Ibid, Ixxxiii, 129. 
