SCIOPTICON MANUAL. 63 



copied in proper position in front of the lens, with noth- 

 ing to shut off the diffused light between the lens and 

 negative. 



In selecting a position for operations, a north light 

 will be found the best suited for the purpose. The 

 upper window sash should be lowered, and the board 

 upon which the cameras are arranged rested one end 

 upon a table, the other upon the lowered sash, so that 

 the negative will have the sky for a background. This 

 is easily determined by focusing upon the ground-glass. 

 It is advisable not to allow the direct rays of the sun to 

 illuminate the negative. Should a north light not be 

 obtainable, cover a frame with white tissue-paper, and 

 let that be the background for the negative. The tis- 

 sue-paper can be illuminated with the sun's rays, or by 

 any artificial light. 



It may seem to the reading photographer, unneces- 

 sary to burden this article with a complete chemical 

 formula for making glass positives, but as it is prepared 

 expressly for the uninitiated, it would be unintelligible 

 without a formula. 



To make 8-02. Sensitive Collodion. Alcohol 5 oz., ether 

 3 oz., iodide of ammonium 44 grs., bromide of magnesi- 

 um 20 grs., cotton (Parys') 35 grs. Before using, filter 

 several times through cotton soaked in alcohol. It is a 

 good plan to keep a supply of plain, unexcited collodion 

 on hand, as a stock-bottle; also, a bottle of exciting solu- 

 tion, made in the proportion of iodide of ammonium 5 

 grains, bromide of ammonium 2 grains, to the drachm 

 of alcohol. By adding 1 drachm of the solution to 1 

 ounce of plain collodion, it will be excited to the proper 

 condition. 



Nitrate Solution. Water 1 ounce, nitrate of silver 40 

 grains; make slightly acid with nitric acid, C. P. Iodize 



