528 
POPULAR SCIENCE REVIEW. 
again treated with dilute alcohol, and the liquor evaporated for a further 
yield of sufficiently pure iodide. Care must be taken to exclude all acid 
vapours from the chamber when the evaporation is carried on ; and it is 
well to add, from time to time, to the solution, a few drops of ammoniated 
alcohol. — Vide Artisan, May, 1864. 
The Combustion of Gun-cotton. — Some curious facts in connection with 
the causes of the slow and rapid combustion of gun-cotton have quite 
lately been pointed out by Professor Abel. He finds that if, even for the 
briefest space of time, the gases resulting from the first action of heat on 
gun-cotton are impeded from completely enveloping the burning extremity 
of the twist, their ignition is prevented. And as it is the comparatively 
high temperature produced by their combustion that effects the rapid and 
more complete combustion of the gun-cotton, the momentary extinction 
of the gases and continuous abstraction of heat by them as they escape 
from the point of combustion, render it impossible for the gun-cotton to 
continue to burn otherwise than in a slow and imperfect manner, under- 
going a transformation similar in character to destructive distillation. 
These facts can be illustrated experimentally, by inflaming in the ordinary 
manner a piece of the compactly twisted gun-cotton, laid upon the table? 
and throwing a jet of air against the flame in a line with the piece of 
cotton, but in a direction opposite to that in which the flame is travelling. 
In the course of this experiment it will be observed that the combustion 
changes to the slow form, because the flame is prevented from enveloping 
the burning cotton and thus becomes extinguished. When, however, the 
current of air is so employed as to throw the escaping gases back on the 
burning cotton, then the combustion passes from the slow to the rapid 
form. — Vide Report of paper read before “ Royal Society by Professor 
Abel, in The Electrician , May, 1864. 
Decomposition of Uric Acid by Bromine . — In a memoir presented to 
the Academy of Sciences, M. Hardy alleges that though bromine gives no 
substitution products with uric acid, yet in the presence of water it splits 
it up into alloxan and urea, forming at the same time hydrobromic acid. 
If the temperature be high, more complex changes take place, and para- 
baric and oxalic acids are formed, with some hydrobromate of ammonia. 
Chlorine and iodine give results similar to those of bromine. When 
alloxan is heated to 160° C’., it loses two atoms of water; if the heat be 
carried to 250°, it loses no more water, but acquires the property of giving- 
coloured solutions. When treated with a base, this modified alloxan fixes 
two atoms of water, and forms an acid identical in composition with 
alloxanic acid, but which gives coloured salts. For this M. Hardy suggests 
the term Iso-alloxanic acid. From these researches, he is also led to infer 
that the purple compound produced in the “ nitric acid and ammonia ” 
test for uric acid is not murexide, but simply iso-alloxanate of ammonia. 
— Vide Comptes Rendus , lviii., 20. 
Peculiar Properties of Hydrocyanic Acid. — The following may be 
given as the general conclusions at which MM. Bussy and Buignet have 
arrived : — 
1st, When this acid is mixed with water, the temperature is very 
decidedly diminished, and the volume of the mixture contracted. 
