L. TECHNOLOGY. 499 



of water, then adding a quart *of water, and afterward, for ev- 

 ery tenth of a quart of the liquid, 15 grains of iodide of po- 

 tassium, 45 grains of chloride of potassium, and 1| grains of 

 bromide of potassium are to be introduced, and, when dis- 

 solved, the whole boiled for 10 minutes, allowed to stand for 

 a day, and then decanted and filtered through linen. Twelve 

 to 20 sheets of the paper are immersed in this liquid at a 

 time, or can be floated -upon it for 15 or 20 minutes, and then 

 hung up to dry in a dark room. Should the paper assume a 

 dark color it will be of no consequence, since this tint will 

 disappear in the silver-bath. This bath is to be prepared in 

 the proportion of 1 to 15, and for every ounce of nitrate of 

 silver 50 to 60 grains of citric acid are to be added. The de- 

 veloper is made of 50 grains of pyrogallic acid and 80 grains 

 of citric acid in 30 ounces of water. The time of exposure 

 varies from 10 seconds to 25 minutes, according to the pic- 

 ture to be copied and the actinic force of the light. 8 A, 

 May 1,90. 



SIMPLE METHOD OF COPYING DEAWIXGS, ETC. 



Silvered albumen paper, after being washed, may be con- 

 veniently used for copying negatives as well as positives. It 

 keeps for weeks, and becomes sensitive to light only after ex- 

 posure to the vapors of aqua ammonia, technically termed 

 " smoking with ammonia." Dr. H.Yogel has greatly simpli- 

 fied the latter process by substituting for the liquid ammonia 

 the powder of carbonate of ammonia. lie thoroughly im- 

 pregnates a piece of felt or cloth with' this powder, and lays 

 it under the silvered sheet, separated from it by a piece of 

 blotting-paper. The negative is placed on the top, and the 

 back covered, and the whole is ready for the copying frame. 

 One impregnation with the carbonate of ammonia serves for 

 several copies. So very simple .is the operation that. Dr. Vo- 

 gel has made use of it in public libraries for copying compli- 

 cated drawings. He places the silvered paper, with the sub- 

 stratum of carbonate of ammonia arid the drawing on top, 

 between two plates of glass, and, exposing it to the light of 

 the window, obtains a copy quite distinct in all its details, 

 while he himself may be occupied with reading or otherwise. 

 The copy obtained is, of course, in white lines upon black 

 ground. Such photographs merely require to be treated with 



