390 Scientific Intelligence. 
required for the preparation of oxygen from potassic chlorate. With this 
arrangement the loss of material is inappreciable. Each kilogram of 
cuprous chlorid yields 28 to 80 liters of oxygen 
A very simple modification of this method permits the preparation of 
chlorine gas with equal facility. If after oxydation chlorhydric acid gas 
be conducted over the cuprous oxy-dichlorid, the latter becomes cupric 
chlorid, €uCl,. t a red heat, this salt decomposes into cuprous chlorid 
and chlorine.—Z/Jnstitut, 1867, p. 61. 
10. Apparatus for detecting differences of density in transparent media. 
—Dr. A. Térrer has given a new method of observing certain import- 
ant phenomena which escape attention by direct vision more or less com- 
pletely. His pamphlet, “Beobachtungen nach einer neuen optischen 
oO 
Methode, Bonn, 1864,” is not at hand; but from a very complete synopsis » 
(with quarto plate) in Erganzungsblatter ziir Kenntniss der Gegenwart, 
Hildburghausen, 1866, i, 88, and from his article on the application of 
this method to microscopic observations, in Pogg. Ann., 1866, exxvil, 
556-580, we give the following: 
Let A be a radiant; a good lamp surrounded s 
with a brass cylinder. The latter has a circular a LM BT 
opening, in front of which is placed a small ver- 
' tical metallic screen with holes near its edge for 
the transmission of the light from A. This pencil of light falls upon 4 
7 
slide of Bunsen’s spectroscope. This is the “ Schlieren ”- apparatus, which 
pears. But if L is not perfect, if it contains a flaw, f (i.e, 
then this will refract light differently from the body of the lens; the rays 
from f will not collect in B; when s has nearly reached B, many of the 
