270 HOW TO \VOKK 



camera or at the vertical frame, or from the slide-holder, or when 

 preparing the plate in the darkened room, or before applying the 

 fixing solutions, or if the nitrate bath and chemicals be not in perfect 

 condition, the plate when cleared will appear fogged or misty, and 

 not yield good prints. 



Generally it is advisable, when the negative appears correct, to 

 take a second one under the same arrangements, only re-arranging 

 the prism seldom can the exact relations be re-established, and after 

 the rendering of another negative, it may be found that the little 

 alteration in the illumination, barely visible on the screen to the eye, 

 has given a still more perfect character to the image, or further 

 developed some of the finer markings. 



3-45. Of increasing the Intensity of the Negative. There is much 

 difficulty in obtaining a clean dense negative, which shall preserve 

 distinctness in the finest markings. When the attempt is made to 

 procure greater intensity by the intensifying processes, the fresh 

 deposit of silver, with the shrinking of the collodion in drying, will 

 often so completely close up these lines, that their definition becomes 

 lost in the print. To endeavour to still preserve these and add 

 printing intensity to the negative, some employ a solution of bichloride 

 of mercury. Dissolve in 2 oz. of distilled or soft water, 12 grains of 

 the bichloride of mercury or corrosive sublimate ; label the solution 

 POISON. After developing with iron, washing and continuing the 

 development with the silver and pyro solutions, fixing, and re-wash- 

 ing, the plate is flushed with the sublimate liquid (which is allowed 

 to remain on, until the image becomes of a dark grey colour if the 

 solution be used weaker, 2 grs. to the oz. of water), then well washed, 

 and recovered with a weak solution of iodide of potassium from i to 

 2 grs. to the oz. of water ; this will give the image a dirty grey or 

 green tinge, which will often dry of a darker colour. The bichloride 

 can also be used after the iodide of potassium solution, taking care 

 to wash the surface well before applying it, then again washing off 

 with water, the plate may be covered with an old weak solution of 

 hyposulphite of soda, or a few drops to half a drachm or more of the 

 strong liquor of ammonia in half a pint of water, or sulphide of 

 ammonium in water. Some employ iodide of mercury dissolved in 

 iodide of potassium, and thus secure its advantages by one opera- 

 tion. In cases in which the bichloride has been used to add to 

 the intensity, the negatives, when dry, often present a remarkable 

 sharpness ; but it is no uncommon thing to find that when the 

 plate has been dried, spontaneously even, the moment it is handled 

 the collodion flies and cracks often into the image; to prevent 

 this it is requisite to pour over the plate, after the last washing, a 



