674 
POPULAR SCIENCE REVIEW. 
Williams, of Pittsburg, U.S. Tested at Fort Pitt, a specimen of wrought 
iron made by him was subjected to a strain of 166,9001b. per square inch, 
without breaking, which is nearly twice the endurance of any iron ever 
tested, and is much greater than that of cast steeL The process of imparting 
this unexampled tenacity of strength to iron, adds only two dollars per ton 
to its cost. If after facts justify this test, it will add nearly 150 per cent, to 
the strength of steam boilers, the thickness of plate being the same. Chains 
of equal tractile strength can be made of less than half the iron now used. 
For suspension bridges it will be invaluable. The improvement is chemical 
in its nature, and is applied in the boiling furnace. The iron of which the 
piece which was tested was made, was principally anthracite pig, with a 
small quantity of charcoal iron. 
The Coal Trade. — The quantity of coals, cinders, and culm, shipped and 
carried coastways from port to port of the United Kangdomrose to 10,970,711 
tons in the year 1864, an increase of 382,000 tons over the previous year. 
3,116,703 tons of coal were brought coastwuse into the port of London, and 
2,359,723 tons by inland navigation and land carriage, making in aU 5,476,426 
tons — an increase of 349,000 tons over the previous year, but the increase 
was entirely in the quantity arriving by inland navigation and land carriage. 
8,809,908 tons of coal, cinders, and culm, of the declared value of £4,165,773 
were exported from the Llnited Kingdom to foreign countries and the colonies 
in the year. This is an increase of 534,000 tons over the previous year. 
PHOTOGEAPHY. 
Transferrhig Photographs to Metal for Printing. — Some months since we 
called attention to some very promising experiments in this direction, con- 
ducted by Mr. W oodbury of Manchester. These have resulted in a process 
recently patented, which is likely to assume a very important position in the 
arts. Mr. Fox Talbot has the merit of first pointing out the facts upon 
which it is based. This gentleman, to whom photographers too often forget 
how much they owe, discovered in connection with one of his photo-engraving 
processes that gelatine when dissolved in hot water, if mixed with bichromate 
of potash or ammonia, dried, and exposed to the action of light, would become 
insoluble. A result due to the decomposition of the alkaline bichromate and 
the liberation of chromic acid. It will at once, therefore, be seen that a coat 
of the bichromated gelatine on a glass or metal plate placed under a negative 
and exposed to light, would, when subjected to the action of hot water, be 
dissolved away in some parts, and in other parts unaffected, thus producing 
a photographic positive in relief. Acting on these facts, Mr. Woodbury 
takes the image in rehef so produced, and either by mechanical pressure with 
some soft metal, such as type metal, or by the usual process of electrotyping, 
produces an intaglio impression therefrom. A properly prepared ink, formed 
with gelatine and some black or other coloured pigment, is then passed over 
the plate, with which the impression is filled up even to the surface. Of 
course the gradations of relief in the bichromatic gelatine print, form grada- 
tions of depth in the metal intaglio, in which again the ink, being transparent, 
forms gradations of blackness proportioned to its varying thicknesses. When 
