210 
rOPULAR SCIENCE REVIEW. 
proper confers a peculiar and good effect, and even skilled artists liave been 
deceived by these bold imitations of elaborate work. 
Pnnting Photographs by Mechanical Means . — The expense, loss of time, 
and other disadvantages attendant upon the usual method of printing 
photographs by the agency of silver salts have for several years back acted 
as an incentive to have them printed by mechanical means, so as to provide, 
among other things, for the wants of book illustration. Within the past 
few weeks a process of printing photographs by means of fatty ink, 
discovered by Albert of Munich, has been much spoken of. The complete 
details of the process have not yet been published, but as far as it is known 
it has a strong resemblance to the photo-lithographic process of M. Tessie du 
Motay. A very thick plate of glass is first coated with a layer composed of 
albumen, gelatine, and bichromate of potash, which is then rendered insoluble 
by exposure to the light. On the surface is poured a* similar sensitive 
layer of gelatine and bichromate of potash' dissolved in water. When dry, 
the plate is exposed to light under a negative, after which it is washed and 
treated as a lithographic stone ; for a surface so treated possesses the 
property of absorbing water, and consequently resisting the application of 
fatty ink in the inverse ratio of the action of light, or in proportion as the 
light passing through the negative has not acted upon the sensitive layer. 
The photographs thus printed are said to be very fine, and nearly a thousand 
can be obtained fi’om one plate. 
Plain Paper Prints . — Many photographers are now employing plain as well 
as albumenised paper. Although for several years the latter has been almost 
exclusively used, there now appears to be a disposition to test the capabi- 
lities of plain paper more thoroughly than has previously been done. M. de 
Constant produces fine, delicate, and yet vigorous pictures by employing a 
stout paper sized with arrowroot, sensitising in a neutral silver bath of 
eight per cent., and, when dry, exposing it for ten or fifteen minutes to the 
vapour of ammonia. It is then printed, toned, and fixed in the usual 
manner ; only the gold toning bath must be alkaline, and weaker than that 
commonly employed for albumenised paper. When washed and dried, the 
prints are treated with a warm solution of gelatine, and are afterwards 
finished by the application of weak negative varnish. 
New Lime Light . — A lime light of a simple yet efiective nature has re- 
cently been introduced, and, from the purity and actinic power of the light, 
it is expected that it will prove of great use to photographers. It is the 
ordinary oxyhydrogen or lime light, with a slight difference, however, but 
one which, in its results, may be fraught with importance, being nothing 
less than a substitution of common atmospheric air for the pure oxygen 
hitherto employed. A stream of air is caused to pass through a gas flame 
issuing from a suitable burner, and to impinge upon the lime as in the ordi- 
nary’ o.xyhydrogen light, but the lime is so arranged as to present a number 
of jagged edges to the blowpipe flame, in preference to the smooth surface 
of the common lime cylinder. Lime of a soft quality appears to answer 
better than hard lime ; and magnesia, mixed with lime and asbestos, has 
also been employed with advantage. The cost of the light is thus reduced 
to that of the common gas used, and as from a given volume of common 
gas a more intense light can be obtained in this manner than by the ordi- 
