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POPULAR SCIENCE REVIEW. 
fusible metal mixed with a small portion of mercury, in place of the latter 
only ; when this mixture is melted it acts in the same manner as mercury, 
and when cold the copper may be deposited directly upon it, and the 
necessity for the wax or plaster model, and copper matrix, done away 
with. The methods above detailed are not however suitable for delicate 
work, the removal of the excess of the mercury or of the fusible 
amalgam endangering fine lines. For superior purposes, therefore, M. 
Dulos makes uses of an amalgam of copper which he lays on a silver 
plate, upon which the design is already drawn, by means of a silvered 
roller which deposits the amalgam on the exposed silver portions of the 
plate, but deaves the iron coating entirely free. The Academy of Sciences 
has appointed a commission to report on these processes, and the result is 
awaited with considerable interest. 
Heliochromy.* — A recent report, by M. Niepce de Saint-Victor, to the 
Academy of Sciences, contains much matter of interest, not only as 
regards the photography of colours, but also in connection with the 
great question of the spectrum analysis. It is well known that yellow is 
the colour which presents the greatest difficulties to the photographer, and 
especially in heliochromy ; but M. Niepce de Saint-Victor has at length 
succeeded, as he informs us, in producing the yellow tints with certainty, 
and in connection with other colours. Previously, he says, he could 
obtain red, blue, and green ; but whenever yellow came, it was always by 
accident. The means by which he at length succeeded in reproducing 
yellow tints, was by the substitution of a bath of hyperchloride of soda 
in place of potash. The recipe given for this bath is as follows : — “ Take 
fresh-made hyperchloride of soda, marking G° of the areometre, mix it 
with an equal quantity of water, and add alcohol in proportion of one-half 
per cent, of the soda ; raise the mixture to the temperature of 70° or 80° 
centigrade (say 160° to 175° Fahrenheit), pour it into a flat dish, then 
plunge the silver plate into the bath for a few seconds, agitating the 
solution at the same time, until the plate assumes an almost black tint ; 
then rinse it in plenty of water, dry it over a spirit-lamp, and warm the 
plate as much as necessary. A bath containing six or seven ounces of the 
solution is sufficient for the preparation of five or six quarter-sized plates. 
With plates thus prepared the colours are produced very brilliantly, 
especially by direct contact, and the blacks are often given in all their 
intensity. For the camera, M. Niepce de Saint-Victor recommends that 
the plates should not have too thick a coat of chlorate of silver, and that 
they should be of a fine cherry-coloured tint after being heated ; he also 
says, that the plate should be covered with a varnish with chlorate of lead 
for its basis. As regards the fixing of the colours, M. Niepce de Saint- 
Victor announces, that he has succeeded in getting them to last a much 
longer time than he was formerly able to do, (but not yet in making them 
permanent), and the best means he has yet discovered for this purpose, is the 
tincture of benjamin of Siam, applied to the plate when the latter is warm. 
* The process of photography in which pictures are obtained in their 
natural colours. 
