210 M. Ni^pce de Saint- Victor on some 



layer of starch-paste upon a Daguerreotype silver plate and 

 upon one of copper, the impression of a drawing which I had 

 thought to copy on the layer of starch became fixed upon the 

 metal without leaving any sensible trace on the layer of starch. 

 It was thus evident that the iodine had passed to the metal, 

 in consequence of a superior affinity to that which it has for 

 the starch. 



On Phosphonis. 



1 found that the product of the slow combustion of phos- 

 phorus exposed freely to the air possesses the same property 

 as iodine, of being absorbed by the black parts of an engra- 

 ving or any kind of drawing, whatever may be the chemical 

 nature of the black substance. 



Thus on exposing an engraving to the vapour of phosphorus 

 burning slowly in the air, and subsequently laying it upon a 

 plate of copper, placing it in a press for a few minutes and 

 exposing it to the vapour of solution of ammonia, we obtain a 

 perfectly distinct and thoroughly fixed impression. The im- 

 pression is quite invisible when the drawing is separated 

 irom the plate of copper, and it is absolutely necessary to have 

 recourse to the ammonia to render it visible; just as, if we re- 

 quire to take it upon a plate of silver, this must be exposed 

 to the vapour of mercury, I drew some black and white lines 

 with oil-paints upon picture-canvas ; on exposing them to 

 the same vapour, the black portions only were copied on the 

 metallic plate; that is to say, the black parts being impreg- 

 nated with the vapour, and having been placed in contact with 

 the copper, the vaporized substance acted upon the metal, and 

 the white bands which did not contain any of it left the copper 

 untouched. When this plate was exposed to the vapour of 

 ammonia, the image became very distinct. However long an 

 engraving may be exposed to the vapour of phosphorus, the 

 black parts alone become impregnated with it ; but when it 

 has remained a considerable time, the impression becomes 

 slightly visible upon the plate, as if figures had been drawn 

 upon it with a piece of phosphorus ; and on exposing it to 

 the vapour of ammonia, the impression appears as if in relief. 



A plate of silver or co()per exposed to the same vapour re- 

 produces by contact all kinds of drawings, and yields a posi- 

 tive impression. It must be understood, that to render the 

 impressions visible they must be exposed to mercury or am- 

 monia. 



The vapour of the yellow sulphuret of arsenic (orpiment) 

 heated in the air imparts to an engraving, when exposed to it 

 for about five minutes, the property of impressing its own 



