L. TECHNOLOGY. 503 



RESTORING FADED PHOTOGRAPHS. 



Our readers are well aware o the extent to which the or- 

 dinary photographic prints, made with nitrate of silver, are 

 apt to fade with time, and the danger of entire obliteration 

 that attends many of them. It has been, therefore, an object 

 of extended experiment with many to devise some process by 

 which the pictures can be brightened and the faded portion 

 restored. These experiments are asserted to have been more 

 successful at the Military Academy at Woolwich than else- 

 where, and we are assured that a method has been devised 

 which answers the purpose almost perfectly. 



The pictures are, in the first place, thoroughly impregnated 

 with wax, care being taken to remove all excess by hot iron- 

 ing, subsequently rubbing the surface with a tuft of cotton. 

 This operation itself deepens, the contrasts of the picture, and 

 brings out many minor details previously invisible, the yel- 

 lowish-whites being rendered more transparent, while the 

 halftones and shadows retain their brown, opaque character. 

 This picture, thus prepared, is then used as a negative, a print 

 being taken from it, many details of treatment and manipu- 

 lation too technical for introduction here being required. 18 

 A, January 6,' 364. 



HEATIXG BY CIRCULATION OF PETROLEUM. 



A new method of applying heat has recently been patent- 

 ed in England, and is now in use for working stone-ware 

 pans, such as are required in certain pharmaceutical opera- 

 tions, by which any temperature between 100 and 700 Fah- 

 renheit can be safely and easily obtained and maintained. 



The principle in question is to cause heavy paraftine oil to 

 circulate first through a coil of pipes in a furnace, and then 

 through the jackets of the pans. The oil is carefully select- 

 ed for the purpose from the heaviest of the petroleum prod- 

 ucts, and moved by its own convection. Heated in a close 

 coil of pipe by a coke fire, it rises into an air-tight tank, from 

 which it passes through pipes to the jackets of the different 

 vessels to be heated, returning after it has done its work to 

 the lowest part of the furnace-coil. A continuous circulation 

 is thus maintained, similar to that which occurs in a hot-wa- 

 ter apparatus for warming buildings. After leaving the tank 



