DETITHONIZING POWER OF GASES. 



face in copper by the electrotype after it has been previously Jixed by the agency of a film 

 of gold. 



827. Those who are conversant with these matters will see at once that this is a very 

 different thing from the abortive attempts which were made early in the history of the 

 Daguerreotype. Many artists endeavoured to transfer its surface by precipitating cop- 

 per upon it ; among others, I made trials of the kind. The results of those abortive 

 attempts were mere shadowy representations, which could be seen in certain lights, 

 and which were very unsatisfactory in their effect.* 



828. The beautiful tithonotypes that are now so common in this city are made in 

 the following way : The Daguerreotype is carefully gilt by M. FIZEAU'S process, taking 

 care that the film of gold is neither too thick nor too thin. The proper thickness is 

 readily attained after a little practice. The plate is then kept a day or two, so that it 

 may become enfilmed with air. The back and edges being varnished, copper is to be 

 deposited upon it in the usual way, the process occupying from twelve to twenty hours. 

 If the plate has been properly gilt, and the process conducted successfully, the tithono- 

 type readily splits off from the Daguerreotype. 



829. The reader will understand that, when the process succeeds, the Daguerreotype 

 will be uninjured, and the tithonotype a perfect copy of it. If any portions are blue, 

 or white, or flesh-coloured, they will be seen in the same colours in the tithonotype ; 

 the intensity of light and shadow is also given with accuracy, and, indeed, the copy is 

 a perfect copy, in all respects, of the original. A great advantage is also obtained in 

 the reversal that takes place. The right side of the tithonotype corresponds to the right 

 side of the original object, and the left to the left. In the Daguerreotype it is not so. 



830. Copper tithonotypes were first made in this city by Mr. ENDICOTT, a litho- 

 graphic artist of distinction. 



831. There is no great difficulty in obtaining from these tithonotypes duplicate copies. 

 An expert artist can multiply them from one another. 



832. The problem of multiplying the beautiful productions of M. DAGUERRE is there- 

 fore solved. 



833. I will take this opportunity of making a remark which I intended to have in- 

 serted in my paper " On the rapid Detithonizing power of certain Gases and Vapours," 

 inserted in the March number of the Philosophical Magazine (S. 3, vol. xxii.). Amateurs 

 in the Daguerreotype process are often annoyed by the want of success which fre- 

 quently attends them. They ascribe to the atmosphere, or to the light, or to other 

 causes, their inability to obtain impressions. Most of these mischances are due to the 

 accidental presence of the vapour of iodine, or other electro-negative bodies, in the 

 chamber or about the apparatus. It is incredible what a brief exposure to these va- 

 pours will entirely destroy a picture before it is mercurialized. If the iodine box or the 

 bromine bottle is kept in the same room with the mercury apparatus, that circumstance 

 in itself is often sufficient to ensure a uniform want of success. If the little frame which 

 fits into the back of the camera, and which holds the silver plate, be used in the iodi- 



* Professor GROVE'S voltaic process for etching Daguerreotypes has, however, produced better results than those here 

 alluded to by Dr. DRAPER. See Phil. Mag., S. 3, vol. xx , p. 18. EDIT. PHIL. MAO. 



