CHAMBERS'S INFORMATION FOR THE PEOPLE. 



in a room carefully protected from white light by 

 covering the window with three or four folds of 

 yellow calico, or in a room lighted by a candle 

 coat it, in the same manner as described for iodis- 

 ing it, with the following solutions : I. Nitrate of 

 silver, 50 grains ; distilled water, i ounce ; glacial 

 acetic acid, 2 drachms : dissolve. This is called 

 aceto-nitrate of silver. 2. One drachm of No. I 

 diluted with 8 drachms distilled water. 3. Water, 

 i ounce, saturated with gallic acid, and 2 drachms 

 sp. wine added. Put a quantity of No. 2 sufficient 

 for one sheet into a small capsule, and add if the 

 sheet is not to be long kept before or after ex- 

 posure 2 or 3 drops of No. 3. Apply this to the 

 surface of the iodised paper, and allow it to remain 

 there for about a minute ; then remove the super- 

 fluous moisture by pressure between sheets of 

 white blotting-paper, and place in the camera- 

 slide, which must be kept scrupulously clean and 

 free from dust. If glass plates are employed to 

 support the paper, they should be cleaned after 

 being used. The slide and prepared sheet being 

 now removed to the camera, and the image accu- 

 rately focussed upon the ground-screen, the latter 

 is removed, the slide is substituted for it, the 

 shutter drawn up, and the requisite time of ex- 

 posure allowed to elapse. This, of course, varies 

 with circumstances ; but with good light and a 

 stop half an inch in diameter, it should not exceed 

 four or five minutes. Should the sheet be required 

 to keep good for from eight to twelve hours, it will 

 be necessary to exclude solution No. 3 in prepar- 

 ing it it is only useful when great sensitiveness 

 is required, and when the sheet is to be used 

 within half an hour. 



To develop the picture, the sheet, when removed 

 from the slide in the darkened room, is submitted 

 to the action of I part of solution No. I added 

 to 2 parts of No. 3, and applied to the surface 

 with a brush or pellet of cotton-wool. The picture 

 soon begins to appear, and gradually deepens in 

 intensity. When the highest lights are sufficiently 

 dark, and the parts in shadow are tolerably clear, 

 the action is checked by plunging the sheet into 

 a basin of water, having dissolved in it a table- 

 spoonful of common salt. While the develop- 

 ment is going on, the sheet must be kept always 

 wet with the solution ; and should it present a 

 reddish hue, an excess of No. 3 may be employed. 

 If this has not the desired effect, most probably 

 the exposure in the camera has been too long. As 

 absolute cleanliness is most essential in this as 

 in all photographic processes, all vessels employed 

 should be cleaned for each picture. 



The image must now be fixed. This is done 

 by removing the yellow iodide from the surface, 

 by immersion in 3 ounces of hyposulphite of soda 

 dissolved in 12 ounces of water a gentle heat 

 greatly facilitates this process. The picture is 

 now thoroughly washed in repeated changes of 

 water, allowing it to soak for six hours, and then 

 pinning it up to dry. In order to render the 

 negative more transparent for printing, it may be 

 saturated with spermaceti or with white wax, by 

 the aid of heat. 



WAXED-PAPER PROCESS. 



This is a modi'fication of the plain calotype pro- 

 cess just described, and has been found a very 

 valuable one for landscapes. The most manifest 



780 



advantages it possesses over the calotype consist 

 in the keeping qualities of the sensitive sheet, and 

 its remaining unchanged at higher temperatures 

 than the talbotype sheet is found to do. Most 

 beautiful and artistic pictures are produced by it. 

 The keeping qualities of the sheets render the 

 process a great favourite with many operators, as 

 a portfolio containing the prepared sheets may be 

 carried to a great distance, and pictures obtained, 

 without the necessity of carrying a quantity of 

 chemicals. The process originated in France 

 with M. Le Gray. A short outline of it, some- 

 what modified and simplified, as practised by Dr 

 Keith of Edinburgh, is as follows : Take thin paper 

 (that of Canson freres or Turner for negatives 

 answers very well), and having cut it into sheets 

 of the size required, observe that they be quite 

 dry. Then, having heated a plate of metal until a 

 drop of water let fall upon it boils without running 

 off, cover jit with several folds of blotting-paper, 

 and lay upon this a sheet of the paper to be pre- 

 pared. Rub quickly over its surface a piece of 

 yellow or white wax, and lay on sheet by sheet, 

 rubbing each successively with the wax until the 

 number is exhausted ; apply pressure ; separate 

 them ; allow the whole to cool ; reheat the plate ; 

 cover it with blotting-paper ; and lay on it the 

 waxed paper, interposing a piece of blotting-paper 

 between each sheet ; cover the whole with several 

 folds of blotting-paper, and pass a heated smooth- 

 ing-iron several times over the mass. Remove 

 the uppermost sheet ; re-apply the iron, and repeat 

 the process until the sheets are exhausted. It is 

 important that the wax be equally imbibed, and 

 that all superfluity be removed by the bibulous 

 paper. The purest wax must be used. The 

 sheets are now to be iodised. Take pure water, 

 40 ounces ; iodide of potassium, 750 grains ; 

 bromide of potassium, 250 grains ; sugar of milk, 

 3 ounces ; chloride of sodium (common salt), 

 30 grains ; iodine, 8 grains. Put ten or twelve 

 of the waxed sheets into a flat dish containing a 

 quantity of this solution, removing carefully air- 

 bubbles, and preventing, as much as possible, 

 their coming in contact. Allow them to soak for 

 ten hours, and pin them up to dry. In this 

 state they may be kept good in a portfolio for 

 an indefinite length of time. 



To render sensitive, take nitrate of silver, 360 

 grains; water, 12 ounces; glacial acetic acid, 13 

 drachms (citric acid has been employed with marked 

 advantage instead of acetic 20 to 30 grains would 

 be sufficient in the above formula). Immerse a 

 sheet in this, or float it upon the surface for ten or 

 twelve minutes the dark colour will disappear, 

 this disappearance so far forming a guide to the 

 time during which it should remain in the bath. 

 Air-bubbles will be readily detected by the dark 

 colour remaining at the part. Wash the sheet in 

 a large basin of water, blot off superfluous mois- 

 ture, and the sheet is ready for use when required. 

 The strength of the aceto-nitrate bath must be 

 kept up by adding 2 or 3 grains nitrate of silver for 

 every sheet rendered sensitive. Several sheets 

 may be immersed at the same time. The time of 

 exposure in the camera averages five minutes 

 in good light, with a stop half an inch in diameter; 

 in weak light, a much longer time is required 

 sometimes half an hour. Experience alone can 

 determine this point for every case. 



To develop, place the exposed sheet in a 



