110 Scientific Intelligence. 
or in case of great cane atin to a half-millionth, 
merely a tawny shade n to the s 
It seems scarcely necessary to say that if a very great — . 
acid is used, and too much bichromate, the starch may be 
to reduce the Sdhacinaate: Even this, however, cannot decciva 
for a bluish-green solution is thereby produced, whereas the in- 
dications of iodid are in the order of their strength : blue pre- 
Cipitate, tawny precipitate, tawny solution. Unless in the case 
of very exceptional dilution above spoken of, a well marked 
blue precipitate is always obtaine 
The examination of the delieuey of the reaction yee very 
dilute solutions was made at a temperature of 65° F. or there- 
_ abouts. sp fact requires to be taken into account, as “anos 
e experiments of Fresenius to be found in the Jabres- 
bericht for 1857, the delicacy of the starch test increases as the 
temperature falls, so that at 0° C. a fainter trace can be ren- 
dered evident than at 12° C, and so on: the difference is as- 
sert 
to be material. Fresenius’s experiments were made with 
sulphuric acid ne! hyponitric pat and the delicacy of the reac- 
tion obtaine him at corresponding temperatures seems to 
fall a little short of the above. 
SCIENTIFIC INTELLIGENCE. 
I. CHEMISTRY AND PHYSICS. 
. On the preparation of Hydrofluoric And; by W. P. Dexrer.— 
the cryolite from which the pur sles iscdiuaes: acid is prepared ; 
aperture, is supported by three strips - platinum rivetted to the ne a 
both being made of silver platinum 
A dome’of platinum attached toa leadlon vessel seems to me a half- 
“ Setar. combining the disadvantages attending the use of both 
pan those who are not in possession of an apparatus of platinum, I can 
recommend from experience the following comparatively inexpensive 
arrangem ment. 
It consists of the ordinary leaden en bore, (mine i is 6”’ high by 34’ inter- 
nal diameter,) made of a piece of lead pipe into which a bottom of lead 
is cast, and provided near the top with a small and short tube for the 
escape of the gas. The tube must incline slightly from the retort up- 
