Popular Science Monthly 



weighs about fifteen pounds, is considerably 

 smaller than the professional machine and 

 is operated by a small electric motor. A 

 cell of dry batteries carried in the operator's 

 pocket supplies the necessary current. The 



Developing the film in 

 the form of a coil re- 

 duces the quantity of 

 solution required. 

 About three quarts 

 of solution will de- 

 velop 500 feet of film 



Below: Method of 

 coiling the film over a 

 wood core for immer- 

 sion. A frilled cellu- 

 loid strip is used as a 

 separator between the 

 layers of coiled film 



Corrugated 

 celluloid 

 separating strip 



camera can be 

 loaded in day- 

 light . No 

 tripod is nec- 

 essary. 



The amateur 

 photographer 

 who has de- 

 veloped his 

 own films will 

 require no ad- 

 ditional knowledge for developing the paper 

 motion-picture film. The film is wound 

 around a wood core together with a 

 celluloid strip frilled on the edges. 

 The frill acts as a separator be- 

 tween the layers of the film and 

 at the same time allows the de- 

 veloping solution free access to 

 every part of the surface. The 

 film is rinsed, fixed and washed 

 in the usual manner. It is dried 

 on a collapsible wooden drum. 

 An important feature of Mr. 

 Webb's process is the produc- 

 tion of the positive film. The 

 paper negative film is not trans- 

 parent; therefore a positive film 

 cannot be made by contact. 

 Even if it were possible to do so, 

 it would not prove practical for 

 the amateur, because motion 

 picture film printing by contact 

 is necessarily done by machinery 

 and entails the additional ex- 

 pense of another length of film. 

 A much simpler method has 



55 



been perfected in which the negative is 

 chemically converted to a positive with 

 remarkable results. One solution removes 

 the silver nitrate from the negative ; another 

 bleaches the shaded and dark portions 

 leaving the film 

 blank. On exposure 

 to light, the color 

 values are reversed, 

 the most delicate 

 tones and gradua- 

 tions being retained 

 in the color rever- 

 sion. 



By converting the 

 negative into a posi- 

 tive, it is evident 

 that only one fin- 

 ished positive film 

 can be obtained from 

 each negative. For 

 quantity require- 

 ments, a number of experiments have been 

 made with the half tone or engraving proc- 

 ess as a printing medium. In this process, 

 the positive film is reproduced on a sensi- 

 tized copper surface and etched with nitric 

 acid to produce printing plates. In this 

 manner an unlimited number of positive 

 prints could be produced for circulation 

 purposes, paper and ink being the only 

 material required for the work. As the 

 initial outlay for the half tone plates would 

 be large, this method would prove practical 

 only for quantities running into the 



At left : The screen on which the 

 picture is thrown is in a shadow box 



At right : The projec- 

 tion principle of the 

 cabinet explained. 

 The reflecting mirror 

 is disposed at an angle 

 of 45° under the lid 



