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POPULAR SCIENCE REVIEW. 
be removed from the sensitised sheet, which is then hung up to dry, and the 
same operation is repeated with others, the lower sheets of bibulous paper 
not requiring to be renewed until many sheets of sensitive paper have been 
prepared. 
New Preservative for Dry Plates. — Mr. Carey Lea has found that the 
well-known developing agent, pyrogallic acid, also acts the part of a pre- 
servative for dry collodion plates, giving a greater degree of sensitiveness than 
most of the preservatives now in use. After many experiments, he recom- 
mends the following as being the best way to use it : — A stock solution is 
prepared containing one ounce of pyrogallic acid to eight ounces of alcohol ; 
and of this, which contains rather under sixty grains to the ounce, a half 
fluid drachm is added to eight ounces of water in which has previously 
been dissolved eighty grains of gum arabic and eighty grains of white 
sugar. It is better that the pyrogallic acid be added to the other solution 
just before using. This, in the estimation of the inventor, forms the best 
and most convenient preservative for dry plates hitherto introduced. 
PHYSICS. 
The Bessemer Flame seen with Coloured Glasses and the Spectroscope. — The 
“Chemical News” of January 20 contains a paper on these subjects by 
Mr. J. Spear Parker. With regard to the flame he says, the combinations of 
glasses used by Mr. Rowan and Professor Silliman for observing this flame 
are somewhat similar in their effect, the two light yellow in the one case 
being nearly equivalent to one dark yellow in the other. The combination 
he used was one cobalt-blue glass of rather light shade, and one amber- 
coloured ; too deep a blue he thinks should be avoided, otherwise the flame 
merely shows varying shades of crimson. The appearances observed were 
similar to those recorded by Professor Silliman. On first turning on the 
blast, the flame appeared of a reddish-orange ; after the lapse of a few 
minutes, this gradually changed to crimson, first in flashes, afterwards con- 
tinuously ; the sodium line appearing in the spectroscope at exactly the same 
time, and corresponding also to the flashes ; after a few more minutes had 
passed, the flame altered to yellow, and, at that time, the characteristic Bessemer 
spectrum appeared, flickering at first, like the sodium line j when it became 
steady, the flame, when viewed through the coloured medium, appeared to 
consist of a sheath of a light yellow colour, the inner cone being rose-red, 
while the upper part of the flame was edged with crimson ; this appearance 
was maintained throughout the rest of the decarbonisation, only varied by 
occasional flashes of a deeper red, or of a greenish hue. When the termi- 
nation of the reaction was attained, the flame, after a few premonitory 
flashes, changed again to the crimson colour. The appearance of a crimson 
ring round the mouth of the converter he is inclined to attribute to irradiation. 
Indian Pendulum Experiment. — Col. Walker, Superintendent of the 
Trigonometrical Society of India, has written to the Royal Society to say, 
that he proposes that Captain Basevi should proceed from Karachi to 
England, taking observations en route at Aden and in Egypt, and bringing his 
operations to a close by a series of observations at the Greenwich Observa- 
tory, if the Astronomer Royal has no objection. He mentions the Green- 
