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THE PHOTOGRAPHIC NEWS. VG5. XII. No. 509.—June 5,18G8. CONTENTS. PA GE Bromides in a Collodion Containing a Potassium Salt 265 Pictorial Effects in Portraiture 0•• 266 Echoes of the Month. By an Old Photographer 266 Sketches of Travel from a Sun-painter’s Portfolio 267 “Lux Graphicus”on the Wing 269 A New Mode of Drying Plates. By M. Carey Lea » 269 Pictorial Effect in Photography. By II. P. Robinson 270 On a New and Simple Method of Recovering Metallic Gold and Silver from Residues. By Victor G. Bloede, Chemist 272 PAGE Solar Printing on Canvas 272 Mr. Warren de la Rue’s Photographs of the Moon 273 Proceedings of Societies—American Institute—Philadelphia Photographic Society 274 Correspondence—The Action of Hypochlorous Acid in the Nit rate Bath—Removing the Collodion Film used in Trans ferring Enamels 275 Talk in the Studio 275 To Correspondents 276 BROMIDES IN A COLLODION CONTAINING A POTASSIUM SALT. All who have experimented in the manufacture of collo dion arc familiar with the difliculty of introducing any moderately large proportion of bromide into collodion in the presence of iodide of potassium. Bromide of potas sium is so well known to bo comparatively insoluble that, as a rule, no attempt is made to use it in collo dion. Bromide of cadmium, being very soluble, is most frequently used ; but a difficulty has generally been ex perienced, especially if the solvents employed were highly rectified, in using at the same time an iodide with a potas sium base. A double decomposition has been found to take place, in which bromide of potassium has been formed and precipitated in the collodion. Nevertheless, the use of a portion of iodide of potassium in conjunction with iodide and bromide of cadmium is often de sirable. The potassium salt possesses advantages over other alkaline bases which make it a favourite with many pho tographers. Its presence in a collodion frequently secures intensity, brilliancy, and freedom from fog in degree greater than many of the iodides. The product of its decomposi tion in the silver bath—nitrate of potash—assists, by its deliquescent character, in the retention of moisture on the plate during long exposures, and checks the tendency to matt silver stains. The difficulty of using it witli a full propor tion of bromide has therefore often been a subject of regret with photographers. Mr. Russell Manners Gordon informs us that as the result of some carefully conducted experiments he is able to intro duce as much as two grains per ounce of bromide of cadmium into a collodion containing iodide of potassium without causing a precipitate. The proportion which can be added in the usual mode of mixing rarely exceeds half a grain per ounce. To secure the power we have just indicated a certain order of mixing must be carefully observed, the potassium salt being dissolved in water and the bromides in alcohol of 805 sp. gr. It will readily be seen that in adopting a method of this kind rigid accuracy is required to secure the exact condition in which, without adding too much water to the collodion, a sufficiently aqueous condition is main tained to keep the salts in solution. 1 f the alcohol employed in collodion be much weaker than 820° the collodion will risk showing signs of reticulation ; but if alcohol of this strength be employed in a direct manner for dissolving the salts, the bromide of potassium formed will generally bo precipitated. The first consideration, then, is to ascertain that the minimum quantity of water in which the potassium can be dissolved, and which, when mixed with the alcohol containing cadmium salts, will keep the whole in solution, does not reduce the alcohol below the proper standard for making collodion without reticulation. Mr. Gordon has carefully worked out the conditions necessary. Commencing with alcohol commonly called absolute, but containing really a little over three per cent, of water, it will bo found that the addition of water changes the specific gravity in the follow ing ratio:— To 1 ounce of alcohol ... ... 805 sp.gr. 5 minims of water added give ... 810 „ 10 „ „ „ ,, „ ... 817 „ 20 „ „ „ „ „ ... 822 „ With these fact before him, which have been carefully verified by the aid of the specific gravity bottle, Mr. Gordon proceeds’ as follows :— First prepare the normal collodion after the following formula:— Ether, 725°... Alcohol, 805°, Soluble cotton ... 4 drachms 2 ... G grains Then proceed to prepare the iodizer, as follows :— No. 1. Iodide of cadmium 8 grains Alcohol, 805° 6 drachms No. 2. Iodide of potassium ... ... 8 grains Water ... ... 20 minims Dissolve, and add to No. 1. No. 3. Bromide of cadmium 8 grains Alcohol, 805° 2 drachms Dissolve and add to the above, then filter and keep for use. Then add one part of this mixture to three parts of the normal collodion. Each ounce of the prepared collodion will then contain— Ether } ounce Alcohol, 805° 2 drachms Alcohol, 822° 2 Soluble cotton 0 grains Iodide of cadmium... ... ... 2 „ Iodide of potassium 2 „ Bromide of cadmium ... ••• 2 » “ This,” Mr. Gordon adds, ' I find as good a collodion for the wet process as any I ever used. “ I do not like it for dry plates, as I prefer 3 grains of bromide for this purpose, and the potassium salt will not admit of so large a quantity.”