94 



it also requires no previous steeping in an acid solution. To 

 fix the picture, let it be washed, first in water, then allowed 

 to remain for a few minutes in a solution of hydriodate of pot- 

 assa (five grains to the ounce of water), and washed in water 

 again. The paper I use is the common unglazed copy paper, 

 but such as has a good body. I have tried the same paper 

 with the original preparation, and find it to answer exceed- 

 ingly well ; it does not require in this case, either, an acid so- 

 lution. The same precautions and hints apply to the amended 

 as to the original process : such as when it blackens in the 

 dark, there is too much caustic used ; when it remains yellow, 

 or that it is studded with yellow spots, too much iodine ; when 

 marked with black spots, too much iron. It is necessary to 

 mention these, on account of the varying strength of the ma- 

 terials employed. 



The following is the correspondence laid before the Aca- 

 demy on the part of Dr. Woods : 



" Lacock Abeey, Chippenham, 

 " nth March, 1845. 



" Sir, — Excuse my addressing you on the subject of a Paper 

 which you sent to the British Association at York, last September, 

 containing the description of a photographic process. 



" Some years ago I described a process for obtaining camera 

 pictures without using any second wash. It was described nearly 

 as follows in the specification of my English patent : Take iodised 

 paper, wash it with gallic acid, dry it, and keep it in store for sub- 

 sequent use. This is called io-gallic paper from its constituents. 

 When wanted, take a sheet of io-gallic paper, wash it with nitrate 

 of silver, and put it in the camera. The image obtained is generally, 

 at first, invisible, but it rapidly developes itself when removed from 

 the camera, requiring no further care, except ultimately to fix it. 

 Instead of gallic acid, sulphate of iron answers the same purpose 

 perfectly. The same effect is very often, but not always, produced 

 in the ordinary Calotype process, which I described in 1841; indeed 

 r discovered it in that way. 



" The process which you have called Electrolysotype appears to 



