EECEEATIVE SCIEXCE. 



339 



wliicli it will do in a few seconds, place 

 tne plate upon tke dipper, and plunge it into 



Focussing with tlie T Square. 



the silver bath. ; raise the dipper once or 

 twice, and then allow it to rest for a minute 

 or two. 



The dark frame should be quite free from 

 dust, and a strip of clean blotting-paper, half 

 an inch broad, laid at its lower edge, for the 

 plate to rest upon ; it is very convenient to 

 have a string with a number of these strips 

 attached, hung up ready for use ; they prevent 

 the frame being spoiled, and also the negative 

 from staining. 



The finger-stalls should now bie placed 

 on the thumb and first finger of the right 

 hand, and the plate lifted from the bath ; if 

 it looks greasy on the surface, it must be 

 returned again for a short time ; if the 

 solution flow evenly over, it is ready for re- 

 moval, Take it from the dipper with the 

 finger and thumb, and let the lower edge rest 

 on a sheet of blotting-paper, whilst the su- 

 perfluous silver is wiped from the back ; then 

 place it in the dark frame, take it to the 

 camera, lift the shutter, and remove the cap 

 from the lens. The length of time for expo- 

 sure varies with the subject, the light, the 

 season, time of day, and aperture used, etc. — 

 80 much, that no rule can be given ; half a 



minute may be tried in the first instance, and 

 more or less exposure given afterwards as 

 required. The cap must be replaced, the 

 shutter put down, and the frame again taken 

 to the operating-room. The following solu- 

 tion must be prepared beforehand ; it wUl 

 keep good a few days : — 



DEVELOPINa SOLtTTION. 



Pyrogallic acid . . 2 grains. 



Glacial acetic acid . . 30 minims. 

 Water . . . . 1 oz. 



In very hot weather, this may be mixed with 

 an equal quantity of water before using. 



Kemove the plate from the frame with the 

 plate-holder, hold it in a horizontal position, 

 and pour gently on it at one edge from the 

 developing cup as much of the solution as 

 well covers it. The image will probably 

 begin to appear in a few seconds, and con- 

 tinue gaining intensity for some minutes. 

 Keep the solution in motion, and when the 

 negative has gained sufficient intensity, pour 

 it ofi", and wash well with water ; then place 

 it in a dish containing — 



Hyposulphite of soda . . . . 4 oz. 

 Water 10 oz. 



When all the creamy colour has disap- 

 peared, wash again well with water, and rear 

 up the negative to dry, which should be 

 accomplished rather soon, or it is apt to lose 

 a little of its intensity. Should the plate 

 have been under-exposed, the contrasts will 

 be too strong in the negative, and a want of 

 half-tone. If over-exposed, the image will 

 be flat, and wanting in intensity. If the 

 exposure has been right, and the operation 

 properly performed, the result will be a nega- 

 tive capable of producing any number of 

 prints. When dry, the surface of the picture 

 must be protected by pouring on it whilst 

 warm the varnish prepared for the purpose, 

 and allowing it to harden. 



The whole operation is exceedingly simple, 

 and can be performed in much less time than 

 is taken in describing it. If good materials 



