30 



The operation is then continued, as I have just described, for the 

 second preparation of the new plate, and beginning with the 

 employment of alcohol. 



ON THE UNFIXED IMPRESSION (HUT WHOSE SENSIBLE LAYER 

 HAS BEEN REMOVED IN THE ORDINARY MANNER.) 



First, the plate must be rubbed with alcohol and rouge, in order 

 to remove the traces of oil which serve for receiving the foregoing 

 impression. 



We afterwards proceed, as indicated above, for the new plate, 

 beginning with the employment of alcohol. 



OBSERVATIONS. 



On Iodizing, The colour of the impression depends on the tint 

 given to the metallic iodide ; it may, therefore, be varied at will. 

 However, I have found the violet rose colour most suitable. 



For transmitting the iodine to the plate, the sheet of cardboard 

 may be replaced by an earthenware plate, deprived of enamel. 

 The iodine transmitted by this means is not decomposed; it is 

 useless, I may even say injurious, to heat the plate before exposing 

 it to the vapour of iodine. 



Washing with Hyposulphite of Soda. In order to remove the 

 sensible layer, the solution of hyposulphite of soda must not be 

 too strong, because it destroys the sharpness of the impression. 

 Sixty grammes of hyposulphite are sufficient for 1 quart of dis- 

 tilled water. 



APPENDIX. 



We subjoin the formula for making a few of the solutions used 

 in the Daguerreotype process; but we must caution those who may 

 be ignorant of Chemistry, that some of the substances used, are 

 deleterious and corrosive, and that great care should be taken that 



