IMMERSING THE PLATE.
As soon as the collodion has set, the plate is placed on the clipper and gently lowered with one continuous sweep into the silver bath. Stoppages in immersing the plate, if of any appreciable duration, are liable to cause marks. The silver bath is supposed to have been poured into the upright bath already referred to. All the operations up to this point may be carried out in broad daylight without fear of clam age, but after this a chill orange light only is permissible. Wet plates vary consider ably in rapidity, and at the best they are much slower than an ordinary dry plate. It may be borne in mind that the silver iodide is not formed in the instant of im mersion, and sensitising may therefore be commenced in white light without harm being done. When the plate has been im mersed an instant, it is advisable to move it up and clown in the bath until all greasi ness has disappeared ; in this way the ether is swilled off the surface, and an even sensitising action insured. If using a flat
porcelain dish, the same result may be secured by rocking. The plate should re main in the bath for about three minutes. The exact time is governed by (a) the tem perature and (b) the sensitive salt to be formed. The higher the temperature, the shorter the immersion. In summer, only two-thirds of that required in winter will be necessary. If the iodide only is to be formed, slightly over two minutes will suffice at ordinary temperature ; but in winter a little over three minutes may have to be given, unless precautions are taken to keep the bath at an even tem perature of GO' F. When the bromide has to be formed, the operation 'takes longer, six minutes being necessary in extreme cases ; and greater care is required, as the plate will be more sensitive.