The Optical Magic Lantern Journal (October 1890)

26 _—_— utility. It must be remembered that no process is universally applicable ; and that it requires a little care to use either method according to the particular shade of the object photographed. In a specimen of the cerebellum stained with santal wood, I have been able to copy the shade of the original almost exactly, while it isan approximation of the colour of picrocarmine and carmine, although hardly so red. The next step was an easy one. Given that the action of a 2 per cent. solution of potassium ferrid-cyanide (Ke Fer Crys) is to form a pale whitish image of silver ferro-cyanide, then let the plate be well washed toremove the free ferro-cyanide from the gelatine,and afterwards flood it with a solution of ferric chloride. The image will turn to an opaque blue, which can be rendered transparent if the silver chloride is dissolved outin sodium theosulphate. This latter method gives an image in Prussian blue; but the method is more casily worked for lantern slides than any hitherto described, the other methods, such as that of Benecke of St. Louis (quoted in “ Anthony’s Bulletin "), requiring long exposure in sunlight. “ These last methods are particularly applicable to tissues such as the central nervous system, which are generally stained by difi .se protoplasmic stains like carmine or soluble aniline blue ; for the latter the blue method is an exact imitation. By stopping out different parts of the negative I have been able to combine both colours—obtain, as it would appear, a double Stained slide. The trouble, however, is considerable, and the number of specimens to which it appears applicable are few. Although I have been able by modifications of the method to obtain a three-coloured slide, I cannot at present recommend it to you to copy. “The chemical changes involved in t':ese processes are probably something of the followin: nature :— “The potassium ferri-cyanide is redu-ed by the free stlver in the plate, silver and potassium ferri-cyanides being formed thus :—4Ag + 2K, Fe? (CN) Agi Fe (CN). = 3K1 Fe (CN), ; the potassium ferri-cyanide then forming uranyl ferri-cyanide by double decomposition :—Ki Fe (CN)« + 2U0, (NOa )2 == (UO: )a Fe (CN)i + 4KNO, “In the blue process, the silver ferri-cyanide being alone left in the film by the prolonged washing, reacts with the ferric chloride, forming Prussian blue :— 3Agi Fe (CN); + 2Fe: Cle== (Fes )e 3[Fe (CN)c]! around this frame. * r2Ag Cl. . The Optical Magio Lantern Journal and Photographic Balarger. “ These reactions have been repeated by ordinary | chemical methods by Professor Lapper and myself in: the laboratories of the Royal College of Surgeons of Ireland, and have been found to agree with those observed in the gelatine film. “T may mention for the benefit of any who may wish to use these methods a few facts which I have observed during my experiments. “In order to avoid staining the plate itis advisable to use the toning solution fresh. Although the solution will act a second time, the second plate in my hands always has had a yellow tone when it should be colourless. This yellow colour can be removed by dilute alkalies, but at the risk of unnecessarily reducing the picture in colour. “Ifthe colour is not satisfactory after the plate is washed, it canin white light be put into some alkaline developer. I found hydrokinone and potassium carbonate satisfactory. By this means the uranium will be removed and the ferro-cyanide of silver reduced to its original condition or with very little noticeable change. The toning process can be repeated or modified. “Ttis also requisite to avoid any traces of sodium theosulphate or developer in the film, because they are all active reducing agents, and staining will be sure to follow. “Asa saturated solution of alum appears to have no deleterious effect on the uranium colour, it can be used with advantage after washing to remove any traces of the above reducing agents. This it appears to perfectly accomplish.” —~ -=-10: Reminiscences of my First Lantern Show. By ALR.W. Or late years the ingenuity of man has perfected various methods of supporting and securing screens ; but in years gone by, when I was a young man, these new-fangled things were unheard of, and in these days some rather primitive methods were resorted to, when setting up the apparatus fora lantern show. I was at one time considered the scientist of the village where I lived, perhaps because I owned a magic lantern and some hand-painted slides. However, let that pass. I remember on one occasion when the quietude of our village was disturbed by the fair day, I was prevailed upon to wind up the day by giving a public show in the largest hall available, the munificent sum of five shillings being subscribed to meet my expenses. The loft (hall sounds better) was a somewhat long roomabout loft. high, and duing the afternoon I busied. myself with the aid of my son in erecting a screen, in the middle of the room. First I placed a plank of wood against the ceiling, and then with two uprights from the floor secured this in position, also placing a plank of wood on the floor under the ends of the uprights. The standards being a shade longer than filled the space, they were nice and firm when forced: to the perpendicular ; the screen was then tacked In due time everything being in readiness, the conGenscr warm, and the gas bags in good order, the audience were admitted, and ranged themselves on plank seats on either side of the screen. All being in : place the first picture was projected on the screen. This. if I remember right was a wan szwellowing rats. This caused a stamping and shouting, such as would eclipse a more civilized audience, and made the teams of the floor spring, which in turn made the fit of my uprights somewhat loose, and as Ivck would have it the screen framework, &c., fell over towards the lantern ; the cross beam, which was placed against the ceiling, was held to the uprights by the sheeting being tacked well all round, and crash—the frame knocked the lens out of the flange, and the lantern over. After peace was restorcd and the audience dismissed, I examined the apparatus, and concluded that the five: shillings I received hardly compensated for a broken