658 
POPULAR SCIENCE REVIEW. 
powder, having the valuable properties we have enumerated. — Vide Comptes 
Bendus, August. 
The Oxidation of fatty Vegetable Oils is treated of very fully in a memoir 
of M. Cloez, in which he treats of the influence of light and heat on the 
oxidation. The author’s results are of much interest. He exposed oils to 
the air in colourless glass vessels, and also in vessels of red, yellow, green, 
and blue glass, and also left some oil exposed to air in total darkness. After 
ten days’ exposure, the increase of weight was greatest in the colourless glass 
vessel ; it was rather less in the blue glass ; was very small in the red, 
yellow, and green ; and no increase of weight at all was observed in the oil 
exposed in the dark. Like results were found after twenty days ; but after 
thirty days’ exposure the results were somewhat different. The increase of 
weight was greater in the coloured glasses than in the uncoloured, green 
showing the largest increase after 150 days’ exposure. It is worthy of notice 
that poppy oil, after a time, oxidized faster in the dark than when exposed to 
coloured or white light. Oil heated in atmospheric air oxidized much more 
rapidly than cold oil. The oxidation may be accelerated without heat by 
adding some oil already oxidized. — Vide Comptes Bendus, August 21. 
New Reactions of Gelatine. — Mr. Carey Lea, of Philadelphia, the well- 
known correspondent of the British Journal of Photography, having for 
years devoted himself to the study of the reactions of gelatine, now 
announces the discovery of a colour reaction, which is quite novel. Hitherto 
faintly coloured compounds of gelatine, with a colourless reagent, have been 
obtained, but in the instance described by Mr. Lea the change from a colour- 
less to a highly-coloured solution is well marked. When a piece of gelatine 
is dropped into an acid solution of pernitrate of mercury, it gradually 
assumes a strong red colouration, and after a time dissolves in it completely, 
at ordinary temperatures, to a fine red solution. This solution deepens a 
little if boiled for some minutes. By chlorate of potash the hot solution is 
quickly decolourized, and passes to a pale dirty yellow. This red colouration 
seems to require a certain amount of time for its production, which cannot 
be replaced by heat. If a piece of gelatine be immersed in the solution 
of protonitrate, and boiled for some minutes, it is dissolved, but the solution 
thus obtained is not red, but yellowish. It is to be regretted that the 
reaction here described is not more delicate. It is only striking when 
tolerably strong solutions of gelatine are employed. When the solution is 
very weak, as, for example, if the gelatine constitutes only one half of one 
per cent, of the mixed liquids, the limit of the delicacy of the test is reached. 
Such a solution by standing twenty-four hours exhibits a light but distinct 
pink colour. Although this delicacy is not what may be desired, still coUoid 
organic substances are so comparatively difficult of qualitative detection as a 
general thing, that the method is not without value. The experiment was 
next extended to meta-gelatine. A neutral meta-gelatine was prepared in 
the following manner : — Gelatine was set to swell in cold saturated solution 
of oxalic acid, and then a moderate heat was applied for a sufficiently long 
time for the mass to remain quite fluid when cold. It was then agitated 
with precipitate carbonate of lime until the whole of the oxalic acid was got 
rid of. Meta-gelatine prepared in this way was kept for months in a 
corked phial, in a warm room, without showing any disposition to putrefy. 
