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Tapioca Paper

To prepare tapioca paper, which is very useful for copying photographs by artificial light, 200 grammes (6) Troy ounces) of tapioca are the plate. It is particularly essential when soaked for 2 days in an equal weight of wathe bath has been in long use and is "satu-ter; 10 litres (about 21 pints) of water are rated" with ether and alcohol from the plates. added, and afterwards, for every litre (quart) 3152. Re-developing

Solution, for of liquid, 10 grammes (154 grains) iodide of adding vigor and intensity to the negative, is potassium, 30 grammes (463 grains) chloride of made of water, 1 ounce; pyrogallic acid, 1 potassium, 1 gramme (15) grains) bromide of grain; citric acid, 1 grain. Pour into a small potassium, are dissolved, and the whole beaker or cupping glass about 1 ounce of this boiled for 10 minutes, allowed to stand for a solution, and add, by means of a pipette, 5 or day, and decanted and filtered through fine 6 drops of a solution of 20 grains nitrate of linen. The paper is immersed, 12 or 20 sheets silver dissolved in 1 ounce water . Imme- at a time-or can be floated upon it-for 15 diately flow this solution over the plate, occa- to 20 minutes; it is then hung up to dry in a sionally returning the solution to the little dark room. beaker glass. As soon as the solution begins that is of no consequence, as it disappears in If it has assumed a dark color, to assume a wine color, it is acting with vigor the silver bath. This is to be prepared in the on the negative and should be closely watched, proportion of 1 ounce nitrate of silver, 50 to that the negative does not become too intense. 60 grains of citric acid in 30 ounces of water. When sufficiently dense, throw away the solution and thoroughly wash both the negative and the glass. The latter should always be kept perfectly clean and free from any deposit from the re-developing solutions. from Photographic Solutions.

The time of exposure varies from 10 seconds to 25 minutes, according to the picture to be copied and the actinic force of the light. 3158. Τo Recover Gold and Silver 3153. Negative Varnish of excellent silver and gold waste that result from photo- The quality can always be secured at the dealers graphic operations are best collected in a in photographic materials. In an emergency large bottle or jar, together with anything common shellac varnish, somewhat thinned else that might contain either of the two down with alcohol, and filtered through cotton, metals. When the bottle is nearly full, pour will answer the purpose. (Sec No. 2935.) a little hydrochloric acid and a solution of 3154. The Causes of Failure would green sulphate of iron (copperas) into it, almost require a chapter by themselves; a long and let it stand on a warm place until the experience convinces us that nine out of every supernatant liquid appears perfectly clear. ten failures occur from a want of care, the presence of dirt, negligence. One cannot be over-nice, careful or cleanly-the best results always rewarding the most painstaking.

Add then a few drops more of the hydrochloric acid and iron solution, and observe whether a fresh precipitate forms or not. In the latter case, draw the clear liquid off by means of