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JUNE 15, 1883.] THE PHOTOGRAPHIC NEWS. 375 M. Lisbonne's Emulsion.—M. Lisbonne has worked out a theory of emulsification which leads him to maintain that the maximum of sensitiveness is attained by the presence of neutral bromide of silver. In the preparation of emulsion, therefore, the aim is to eliminate the bromo-hydric acid. When acid, the emulsion is only slightly sensitive, when neutral it is at its maximum of sensitiveness ; if alkaline it fogs. The bromo-hydric acid must be neutralised by ammonia, and at the same time transformation into an alkaline bromide is to be avoided. M. Lisbonne is, perhaps, in the right, and what is certainly true is, that up till now the question of gelatino-bromide has not been brought up to a satisfactory point of scientific precision. Leon Vidal. NOTES ON THE DEVELOPMENT OF GELATINE PLATES. BY W. B. ALLISON.* This subject will doubtless be already well understood by the majority of those present, but perhaps a few remarks based upon my own personal experience may not be amiss. In the first place, taking the developer most used hereabouts, and with which you all are familiar, viz . alkaline pyrogallic, composed of pyrogallic acid or “ pyrogall 1," and ammonia, a suitable proportion of some soluble bromide being added as a restrainer. It is useless my giving a formula for a developer so well known, and which, moreover, requires modification to suit idiosyncrasies of various kinds of dry plates, a plate coated with an emulsion containing a large proportion of gelatine to haloids of silver requiring considerably less restrainer than one in which the emulsion does not contain bo much gelatine. Some commercial plates you will find are coated so thickly with gela tine that scarcely any bromide is required in the developer, whilst others are just the reverse. This developer is, on the whole, the most useful one, as it allows such a great latitude in exposing the plate, and in deve loping ; by ringing the changes upon the fore-mentioned chemicals you can suit its necessary requirements. An over-exposed plate may be successfully developed by using at first the usual quantity of pyro in conjunction with a small quantity of ammonia, &c., or, if known to be much over-exposed, it may still be successfully developed by adding a small proportion of citrate of soda to the developer, which is a powerful restrainer. The yellow stain generally caused by alkaline pyro is best re moved by soaking the plate in chrome alum solution for a con siderable time. Additions, such as glycerine, sugar, sulphite of soda, have been used by some in this developer, but for my own part I can see no great advantage to accrue from their use. Glycerine I have found to be a wonderful aid to the formation of most obstinate air-bubbles, and also film staining, besides slowing the action of the developer. If the pyro must be used from a solution, make the same in water only, so much to the dram or ounce, before commencing development. Use a good plate, and plain alkaline development will suit it, and yourself. I will say nothing as to sulphite of soda in the developer, except that once when using it I obtained the most remarkable specimen of greyish-green fog that has ever been my lot to see ; of course that may have been my own fault. Common washing soda has been recommended by some in preference to ammonia in the pyro developer. It gives yellowish images ; in my opinion, it has no advantage over ammonia. The ferrous oxalate developer is the one which should find a place in the portrait studio ; it is easy to prepare, and one lot will develop a whole day’s negatives, the cost not exceeding that of pyrogallic. Make a saturated solution of green copperas in hot water ; when cool, bottle it off, adding to each bottleful a drop or two of oil of vitriol. Dissolve some oxalic acid in the same way, so that when cool the acid slightly crystallizes out. Add to the solu tion as much common commercial carbonate of potash as will almost neutralise it (known by slightly reddening blue test paper). To use new, three parts of the latter solution, with one of the former, pouring the potash solution into the iron solution. This will form a bright red solution, and if an approximately correct • Head before the North Staffordshire Photographic Association. exposure has been given to the plates, this will develop many consecutively ; should the images come out too flat, use four or five parts potash solution to one of iron ditto. No bro mide will be required, as the sulphate of potash found in mixing the two solutions acts as a restrainer in a slight degree. I have sometimes found that the addition of hyposulphite soda to this developer to force up a picture, and has caused a deposit of the ferrous oxalate salt upon the plate, like fine sand, and spoiling the negative. I do not propose going into the respec tive merits of pyrogallol and ferrous oxalate as developers, having done equally well with either; but on account of the latitude in exposure pyro gives, I usually adopt it for landscape, and also microscopical work ; plenty of latitude is allowable with ferrous oxalate, but this having been once mixed I prefer to use it upon plates the exposure of which I am pretty certain about. 1 show ferrous oxalate and citro-oxalate negatives, the latter being developed by a mixture of oxalate and citrate of potash and ferrous sulphate. Other organic salts of iron, as the boro- tartrate, &c., possess developing powers, but not to compare with the above in efficiency or cheapness. I show two plates deve loped by hydroquinone. No. 1 had two grains hydroquinone, and one minim ammonia. No. 2, two grains hydro-quinone, and two minims ammonia, and no restrainer. This is an excellent developer. The plate requires a shorter exposure than usual, and the image comes up well, and free from stain. The present price of hydroquinone as compared to pyrogallol unfortunately pre cludes its general adoption as a developer. Our Elementary Lessons on Optics, which, we announced three months ago, to be written by Captain Abney, will commence next week in these columns. The beautiful photo-engraving process of Herr Klic, of Vienna, of which we gave an example in the YEAR-BOOK for 1882, has been purchased, so far as Great Britain is concerned, by Messrs. T. and R. Annan, of Glasgow. Our readers will be interested in Dr. Vogel’s collodio- gelatine emulsion patent, which appears in another column. All will rejoice to hear that the visit of our courageous observers to far-off Caroline Island has not been in vain. In another column will be found details of the work accomplished by Messrs. Woods and Lawrance and their brethren, and a fortnight hence we hope to place before our leaders a further letter from Mr. Woods, who has promised to send early accounts of all their doings on this tiny islet in the Mid-Pacific. The sky was “ beautifully clear at the time” of the sun being eclipsed, and luminous rays could be seen darting out from behind the black disc of moon to a distance equal to twice the diameter of the sun ; and as this phenomenon lasted for well nigh six minutes, no wonder the photographs of the corona were successful. Mr. H. P. Robinson’s charming picture, “ Way side Gossip,” forms the presentation print of the Photo graphic Society this year, all members of which should apply at once for copies. The picture is printed in carbon. A characteristic specimen of the Ives’ photo-block en graving process may be seen on page 59 of the current number of “Harper,” an Indian vase being reproduced