282 Action of Light on Amylaceous Substances. 
If two 1 per cent. solutions of starch be prepared under the 
same circumstances, and if one of them be kept in the dark and 
the other exposed to the sunlight, the latter will be found to 
exert an action on the polarizing apparatus ; more dextrine and 
sugar have been formed. If very weak solutions be taken (about 
zGg5) and exposed to the sunlight for about eighteen hours, it 
will be found that the solution has lost the properties of the 
original amylum, and more resembles inuline. 
Many substances, such as lactate or citrate of iron, and cor- 
rosive sublimate, limit or neutralize this action of the light; 
while other substances, such as potassio-tartrate of iron, or nitrate 
of uranium, greatly increase it. 
Dextrine and cane-sugar are unaffected by light. 
There is a curious action on oxalic acid. If a 4 per cent. so- 
lution of the acid be mixed with a 1 per cent. solution of nitrate 
of uranium, and the mixture boiled for even a considerable length 
of time, provided this is done in the dark, no change takes place. 
But if the light, even of a clouded sky, have but a momentary 
action, a decomposition, evidenced by the disengagement of gas, 
at once sets in; andif the mixture be placed in the sun, a quan- 
tity of carbonic oxide may be collected. That this action is due 
neither to the temperature nor to the free acid, is evident from 
the fact that at a temperature of zero, and with the employment 
of oxide of uranium, the same results are obtained. 
Direct experiments have shown that animal starch (glyco- 
genous substances) is more rapidly changed into sugar in the 
light than in the dark ; and, remarkably enough, nitrate of ura- 
nium decreases instead of increases the action. 
It is remarkable that animal starch in frogs’ liver is not 
changed into sugar in winter, which is also the case with the 
vegetable starch. 
This might explain why the sugar-forming substances which 
are so abundant in the membrane of the foetus immediately 
disappear after birth. . 
It can scarcely be doubted that light plays a slow but very 
powerful part in effecting changes in the animal body ; and it is 
evident that a knowledge of the substances which accelerate or 
lesson this action is of great importance in medicine. Th 
symptoms of diabetes, and the action which light has been ob- 
served to exert on scrofulous persons, may be adduced as cases 
_ in point. 
M. Cloez has described* two new benzoic compounds. When 
cyanate of potash is mixed with chloride of benzoyle, and the 
mixture heated to nearly the fusing-point of the cyanate in an 
* Répertoire de Chimie, January 1860. 
