182 ANNUAL OF SCIENTIFIC DISCOVERY. 



cation of a solution of protosulphite of iron, acetic acid, and nitric acid, in 

 about the following proportions : 1 quart of soft water, 1 ounce protosulphite 

 of iron, 32 drachms No. 8 acetic acid, 1 drachm nitric acid. These exact 

 proportions are not rigid, but I have found them to be sufficient for the pur- 

 pose of developing the picture. After this is accomplished, it is washed in 

 clean soft water, and then the remaining iodide of silver is dissolved from the 

 collodion film by a solution of hyposulphite of soda, after which the picture 

 is entirely cleansed by the hyposulphite solution by washing as before in soft 

 water. The picture is then dried, either in the open air, or by the aid of a 

 gentle heat, and the process is completed. 



To permanently improve the beauty of the pictures, and to deprive them of 

 a bluish, hazy, and indistinct look, is the object of my third improvement ; 

 which consists in the application of a coating of balsam of fir to the surface 

 of the glass upon which the picture is made, the balsam being confined to the 

 picture-plate by a secondary plate or glass, which is applied to the picture- 

 plate in a manner which will now be described, and which hermetically seals 

 up the picture and protects it from every and any injury not sufficient to frac- 

 ture the glasses themselves. This part of the process will now be described : 



A second plate of glass is prepared, of the same size as that which carries 

 the picture, and is thoroughly cleansed ; the picture-plate is then held hori- 

 zontally, the picture-side uppermost. The balsam is then applied in a line 

 along one edge of the glass, and one edge of the secondary plate is then ap- 

 plied to the edge of the first which contains the balsam. The two plates are 

 then pressed gradually together, by w T hich the balsam is caused to flow en- 

 tirely across the picture toward the opposite edge, and the air is effectually 

 excluded from between the plates. The superabundant balsam is then re- 

 moved by pressing the glasses together, and a thin coating of it only is left 

 upon the surface of the picture. The beauty and distinctness of the pictures 

 are greatly enhanced by this application, the finer lines as well as the dark 

 portions and shadows being rendered far more distinct, and the most minute 

 delineations being brought out and made visible, while the application of the 

 second plate of glass secures the whole from the action of air, moisture, and 

 dust. 



ENGRAVING FROM DAGUERREOTYPES. 



From the Report of the U. S. Coast Survey for 185-4, by Professor Bache, we 

 derive the following information respecting some most interesting and import- 

 ant experiments made under the direction of the Department by Mr. George 

 Mathiot, for obtaining directly, by chemical means, from drawings, engraved 

 plates for printing. The particulars of the experiments are embraced in the fol- 

 lowing extract from the report made by Mr. Mathiot to the Superintendent. Mr. 

 Mathiot says, " During the past summer I have made a number of experiments 

 on the natural-engraving processes proposed by Donne, Grove, Gaudin, Talbot, 

 and Niepce, with a view of obtaining by chemical means, and directly from 

 the original drawings of the survey, copper-plates ready for printing maps, 

 without the long and tedious process of the mechanical artist. So far, I have 

 not determined that I shall obtain a chcmiglyphic process ; yet I have been 



