SCIENTIFIC SUMMARY. 
203 
tically, it is quite possible, while still preserving the simplicity of the wet 
method, as invented by Gay-Lussac, to substitute a bromide for a chloride 
in precipitating silver, and thus remove absolutely those anomalies which 
have been observed to be attendant upon the use of a chloride or of chlor- 
h}^dric acid. — Vide Chemical News^ Jan. 1. 
The Characters of the Mineral Kotchouheite. — The Duke de Leuchtenberg 
recently sent a paper to the Academy of Science of St. Petersburg in which 
he gives a comparative examination of the minerals kotchouheite, hammererite 
and 'Pennine. The author referred especially to the great importance of an 
optical examination of minerals, such as had been conducted in the re- 
searches of M. des Cloizeaux and others. In proof of this, he stated that 
M. KokcharolF, while examining with a polariscope-microscope a mineral 
brought from the Oural by M. de Morny, and supposed to be kammerite, 
found that it presented two optic axes. On this fact he founded a new 
species, to which, in honour of M. Kotchoubey, he gave the name ot 
Kotchouheite.” This mineral, he says, presents itself ordinarily under the 
form of pyramidal crystals. It is of a reddish violet, transparent in thin 
sections, and translucent in thick ones. It is flexible, but is hardly elastic. 
Its hardness is = 2, its density is 2-679. Divided into thin plates and heated 
over the spirit-lamp, it becomes green without losing its transparency ; it 
assumes a violet hue in cooling. In the blowpipe, or under a great heat, it 
loses its water, ceases to be transparent, and becomes of a yellow colour. It 
is attacked by acids, and especially so by sulphuric acid. — Vide L'lnstitut, 
March 10. 
Molecular Phenomena in Iron. — In a paper read before the Koyal Society 
in January, Mr. Gore, F.R.S., of Birmingham, described a novel phenomenon 
in connection with iron wire. The following abstract is given by the 
Mechanics Magazine : — A strained iron wire was heated to redness by a 
current of voltaic electricity, and then, the current being discontinued, was 
allowed to cool. It was observed that there arrived a moment in the pro- 
cess of cooling at which the wire suddenly elongated, and then gradually 
shortened, until it became perfectly cold, remaining, however, permanently 
elongated. No other metal besides iron exhibited this peculiarity, which 
Mr. Gore attributes to a momentary molecular change, and he points out 
that this change would probably happen in large masses of wrought iron 
and would come into operation in various cases where these matters are sub- 
jected to the conjoint influence of heat and strain, as in various engineering 
operations, the destruction of buildings by fire, and other cases. The pheno- 
menon deserves a further investigation, since every fact relating to iron is of 
importance to us. 
A Crystalline Modification of Silicic Acid. — In a paper presented to the 
Berlin Academy of Sciences, and subsequently published in Poggendorff’s 
Annalen, Herr Buth gave an account of the above. There are as yet, 
he said, only two forms of silica known with certainty to exist — one is the 
crystalline and the other is the amorphous. The crystalline silica is quartz 
whose specific gravity is 2'6 ; the amorphous form has a density which varies 
between 2-2 and 2-3. The amorphous silica appears in nature as opal and 
hyalite; such is also the silica dissolved by steam, and that found in 
organised bodies. Herr Jerzsch tried to prove that dense crystalline silica 
