18 PHOTOGRAPHY. 



American edition of Kane's Chemistry, page 450, which appears sim- 

 plest. It is as follows : mix two parts of chromate of iron ground to 

 a fine powder, with one part of saltpeter and expose it on the floor of a 

 reverberatory furnace to a violent heat. Lixiviate the calcined mass with 

 water and add a quantity of sulphuric acid which will convert the neu- 

 tral chromate of potassa previously formed, into the bi-chromate. This 

 salt is then obtained from the solution by allowing it to cool in a leaden 

 vessel. As thus obtained it is of a rich orange red and is soluble in ten 

 parts of cold water. When applied to paper it is of a deep yellow color, 

 much resembling gamboge. 



The apparatus required is as follows: Get a board a little larger than 

 the size of the sheet on which you intend making your impressions ; fix 

 a slight cushion on this, and cover it with a piece of black silk. Make 

 a frame just the size of the board, in which insert a pane of glass. The 

 glass should be as nearly as possible flush with the lower side of the 

 frame, so as to come in immediate contact with the cushion. 



To prepare the paper, which should be as firm as possible, — make a 

 hot saturated solution of the salt, and let it cool. Take the paper, and 

 if you are preparing several sheets at a time, lay them one on the other; 

 dip a sponge in the solution and go over the upper sheet, (on one side 

 only) in a series of parallel stripes, taking care to cover every part. Then 

 make another series perpendicular to the first; in this manner with a 

 little practice, you will succeed in covering the surface uniformly. Take 

 off this sheet and hang it across a string in a darkened room to dry, pro- 

 ceed in the same manner with the next, and so on till you finish the 

 whole. When dry, put them away in a dark place till wanted for use. 



When you wish to make a copy of any object, a leaf for instance, 

 take a piece of the prepared paper of the required size, and lay it on the 

 cushion with the prepared side down, then place the leaf above the paper, 

 set the glass frame over the whole, and clamp it to the cushioned board 

 as tightlv as possible. The closer the contact of the paper- and object, 

 the more perfect will be the impression, and to this end the cushion will 

 be found to contribute materially. If the impression is to be taken from 

 a leaf freshly pulled, it will be found advantageous to press it between 

 paper for an hour before using, to absorb the superfluous moisture. Set 

 the apparatus thus adjusted, in the sun, and let it remain there from five 

 to twenty minutes, according to the opacity of the object. A little ex- 

 perience will soon indicate the precise length of time. Of course if the 

 sun be partially obscured during the process, the paper must be exposed 

 for a longer time. When finished, the photograph should be taken out 

 in a dark room and put away till ready to be washed. It will be remem- 



