SCIENTIFIC SUMMARY. 
341 
by M. Poitevin’s rival competitors, Talbot, Niece de St. Victor, Lemercier, 
Charles Negre, Placet, Woodbury, Pouncy, Paul Pretsch, Cole, James, and 
others, have achieved nothing,* having greater pretensions to permanency 
than a process extant in 1859 had. And yet good and truly permanent 
photographs are almost as much a want of the age now as they have been 
since the art’s discovery, and all our best experimentalists are still hard at 
work in this identical direction. 
Preservation of Photographs. — In a paper read before the Glasgow Photo- 
graphic Association on the 11th of April, Mr. J. Stuart recommended the 
saturation of prints with collodion as a means of ensuring their permanency. 
Since then others have strongly recommended this process as a very valuable 
one, well calculated to effect the desired end, and Mr. Valentine Blanchard 
in a paper read before the London Photographic Society, gave the result of 
some experiments in carrying out Mr. Stuart’s idea. On this occasion the 
Rev. J. B. Reade, F.R.S., who occupied the chair, gave the entire credit of 
the idea to Mr. Blanchard as others have done since, and said the process 
really conferred immunity from fading. Mr. Belton, at the June meeting of 
the North London Photographic Association, stated that it was best according 
to his experience to apply the collodion to the prints somewhat sparingly, both 
before and behind, with a brush, and to immerse them in hot water before 
mounting, so as to render them more plastic. He had used starch for 
mounting, but thought good glue would prove the better material. 
The Collodio- Albumen Process. — Mr. Maxwell Lyte, whose excellent 
photographs have been so often and widely admired, and from whom we 
have so frequently derived hints of great practical value, has introduced a 
modification of the collodio-albumen process, by which it is said to be 
rendered more sensitive. The iodides and bromides he employs are those of 
sodium, and he does not advise the use of salts of cadmium. After sen- 
sitising, the plates are washed and rewashed in a weak solution of salt to 
remove the free nitrate of silver. The albumen is prepared by an ammo- 
niacal solution of chloride of silver, and the plate allowed to dry over a 
capsule of sulphuric acid, in order to absorb all the free ammonia. The 
developer is a solution of protosulphate of iron without acid. The albumen 
used should not be thick, and all the ammonia should have evaporated 
before exposure. 
Photographs in Colours. — M. ‘Poitevin’s photographs in natural colours, 
described in these pages, were recently stated by that gentleman to fade 
even in the dark. 
Oxalic Acid in the Negative Bath. — An editorial article in the u British 
J ournal of Photography,” speaks of the presence of pin-holes in the film and 
insensitive streaks on its surface as frequently due to the presence of 
crystals consisting of oxalate of silver. After explaining how oxalic acid 
may be present in the collodion, the article attributes thereto the formation 
of the above crystals, and says their nature may be readily proved by two 
very simple tests. One is to heat over a spirit-lamp a few of the crystals 
previously washed in a little water and then dried in a small tube closed at 
one end, when if oxalate of silver they will detonate almost like a few grains 
gunpowder, and the other is the placing of a few of the crystals in powder 
on a watch glass, adding a little water with a drop of sulphide of ammonion. 
