182 HISTORY OF PHOTOGRAPHY. 



and eventually the image is presented on both sides of the paper of 

 equal intensity, in a good neutral tint upon a gray ground. These 

 results, it will be remembered, are of a very similar character to 

 those already described as peculiar to the amphitype process of 

 Sir John Herschel. 



THE FERROTYPE. 



This process, which is of remarkable sensibility, was discovered 

 by the author and published in the Athena?uni under the name of 

 the " Energiatype ; " from a desire to group all those pictures under 

 a general head into which iron salts enter as an element the present 

 name is preferred. The preparation of the paper is as follows : Good 

 letter j^aper (Whatman's is the best) is washed over with the fol- 

 lowing solution, viz : Five grains of succinic acid (it is important that 

 succinic free from any oil of amber or adventitious matter should be 

 obtained) are to be dissolved in 1 fluid ounce of water, to which are 

 added about 5 grains of common salt and half a dram of mucilage 

 of gum arable. When dry the paper is drawn over the surface of a 

 solution of ()0 grains of nitrate of silver in 1 ounce of distilled water. 

 Allowed to dry in the dark, the paper is now fit for use, is of a piu-e 

 white, retains its color, and ma}^ be preserved for a considerable 

 time in a portfolio until wanted for use. 



The preparation of this paper is by no means difficult, but requires 

 care and attention. The solutions must be applied very equally over 

 the paper, which should be immediately hung upon a frame or 

 clotheshorse to dry. Extreme care must be taken that the paper be 

 not exposed to light after the nitrate of silver solution has been 

 applied until required for use. Many of the disappointments ex- 

 perienced by the experimenters on the energiatype are occasioned by 

 a neglect of this precaution, as, although no apparent effect may have 

 been produced by the exposure, the clearness of the subsequent picture 

 will be seriously injured. The succinic acid must also be very pure. 

 We shall now briefly describe the method of applying this process 

 to the different purposes for which it is best adapted, premising that 

 the varying circumstances of time, place, and light will render neces- 

 sary such modifications of the following directions as the experience 

 of the operator may suggest. As a general rule, an open situation, 

 sunshine, and, if possible, the morning sun, should be preferred, as 

 the image is sharper and the color produced more intense and less 

 affected b}^ the subsequent fixing process. 



In the camera, for a building or statue, an exposure of half a minute 

 in strong sunshine is usually sufficient; for a portrait, taken under 

 ordinary conditions, two or three minutes are required. 



When the paper is taken from the camera, nothing is visible upon 

 it ; but by attending to the following directions the latent picture will 



