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458 [September 26,1862. THE PHOTOGRAPHIC NEWS. that a revolution will be speedily effected in the preparation of paper for positive printing. Whilst referring to artistic printing, we cannot omit to call the attention of our readers to a short communication in the present number of the News, from Mr. Harmer, on double printing and vignetting, in which he describes the method employed in producing the specimens in the Inter national Exhibition, of which we expressed a very high opinion a few weeks ago. We strongly commend the subject to all our readers interested in artistic positive printing. PHOTOGRAPHIC CHEMICALS: Their Manufacture, Adulteration, and Analysis. Lithia Salts (continued).—Chloride of Lithium is not a difficult salt to prepare. The starting point being the car bonate, this is dissolved in dilute pure hydrochloric acid, until the effervescence nearly ceases, and the acid reaction to test paper is only slight. The liquid is then filtered, if necessary, and transferred to a dish placed over a water bath, which is kept heated until the excess of water and acid has been driven off, and the dry salt is left behind. As the contents of the dish become thick and pasty, they must be kept constantly stirred with a glass rod, and when apparently dry, the heat must be continued for some little time longer, until all the hydrochloric acid is driven off; this may be ascertained by holding a glass rod, dipped in ammonia, over the dish; if a trace of free hydrochloric is present in the latter, it will render its presence evident by the formation of white opaque fumes. When all the free acid has been re moved in this way, add sufficient distilled water to effect complete solution of the mass, and evaporate again, but not quite to dryness. The chloride will be deposited in the form of cubical crystals, resembling common salt. These are deli quescent in the air, and melt at a dull red heat, volatilizing at a white heat, losing, at the same time, a portion of their chlo rine, and becoming converted, by absorption of oxygen and carbonic acid from the air, into carbonate of lithia. When this salt deliquesces in the air, it gradually forms large rectangular prisms withfoursided summits, containing four atoms of water of crystallization. When the aqueous solution of the chloride is rapidly boiled down the same salt separates in the form of needles, united together in feathery tufts, like those of sal ammoniac. Upon being heated, these melt in their water of crystallization, and then dry up, becoming converted into the salt first described. If these feathery crystals are very gently dried, and then thrown upon paper roughly dried, or moved about with the finger, they instantly become opaque, the opacity commencing from the point of contact and gradu ally extending throughout the whole mass; in this state they fall to pieces on the slightest blow, and form a crystalline powder. Both the. latter mentioned hydrated and the anhy drous chloride of lithium deliquesce rapidly in the air, and are very soluble in water and alcohol. When the alcoholic solution is set on fire, it burns with an intense crimson flame. This crimson colour, which salts of lithia communicate to the flame of spirit or gas, is a very delicate test for the pre sence of the metal, and, in a somewhat modified form, is con stantly used at the present time as a test for lithia. Instead of looking at the coloured flame direct with the eye, it is narrowed by placing a slit in front of it, and the flame is then viewed through a prism. The effect of this is to refract all the other colours (such as those given by soda, strontia, &c.) to other parts of the field, and leave the pure red of the lithia unmingled with anything else. This is the branch of analysis to which the name “ spectral ” has been given. We shall probably recur to this subject before long, for the pre sent this sketch will suffice to show the manner in which it is applied to the detection of lithia salts. Iodide of Lithium.—This salt is coming into some little importance as an adjunct to the usual iodizing agents for collodion. The method of preparation not being detailed in books, wo will give it somewhat fully. The best plan is utt well kept up to adopt what is known as Liebig’s process, for the prepara tion of alkaline iodides. One part of phosphorus is placed in a basin, and covered with forty parts of hot water, so as to melt it. When it is liquid, twenty parts of iodine are gradu ally added with constant stirring, taking care to allow one portion to be dissolved before a fresh quantity is added; violent action takes place, and a great portion of the phos phorus is converted into the amorphous variety, which, how ever, in no way interferes with the process, as the amorphous phosphorus unites with the iodine just as well, although not quite so fast. The colourless liquid, which consists of a solu tion of phosphoric and hydriodic acids, P + 5 I + 5 HO = PO 3 + 5 HI, is then poured off from any excess of phosphorus, and baryta water is added, until the mixture becomes alkaline: the whole is now to be thrown on a filter, and the insoluble phosphate of baryta filtered off, and well washed. The solution, which consists of iodide of barium, with a trace of free baryta, is then to be evaporated to dryness over a water bath, with constant stirring, and the dry residue heated to the fusing point. It is now to be redissolvcd in water, ad' filtered, when it will consist of almost chemically Pl iodide of barium. To this, sulphate of lithia (prepared. 82 shown in our last chapter,) is to be added in quantity jus insufficient to precipitate all the baryta, and the mixtun, containing the precipitate suspended in it, is boiled down to about one-half its original bulk. When sufficiently concel- trated, it is allowed to cool, and is then filtered through a double thickness of paper. To the filtrate a small quantity of pure carbonate of lithia is added, which removes the W portions of baryta, and the solution being evaporated down, yields pure iodide of lithium. This process is very simple in practice, although somewhat complicated to read, and has the great advantage of yielding a perfectly pure product Iodide of lithium forms very deliquescent, acicular crystals which contain six atoms of water of crystallization. The are very soluble in alcohol, and are, therefore, well adapted for employment as an iodizing agent in collodion. , The other salts of lithia are very little known, and ared no special interest to the photographer. Baryta Salts.—The earth, baryta, is of importance, botb on account of the special value of some of its compound* as well as its employment as a test, and re-agent in tb preparation of other salts. In the above description * the method of manufacturing iodide of lithium, baryta wal is used, and in very many similar operations it is a employed. Caustic baryta is best prepared from the nitraf This salt is thrown in small quantities at a time into 8 red-hot crucible, the cover being put on, and the heat hew well kept up between each addition, until the mass b become quite solid. Too much nitrate of baryta must» be added at once, as the salt is apt to boil over. When1 crucible is half-full of baryta, the heat is raised to a bri6 red heat, and kept there for a quarter of an hour. * crucible is then allowed to cool, and is broken up in ord to remove the baryta from it. Baryta in this state fort greyish-white, porous friable mass. When moistened'') 1 water it falls to pieces, and becomes very hot, the heat be1 often sufficient to raise the hydrate produced to rednc and then fuse it. It forms a white powder, fusing at a red heat, forming an oily liquid. It dissolves in teca parts of cold, and in two parts of boiling water, formi’on colourless solution, which deposits the crystalline earm cooling: the cold solution, when exposed to the air, beco covered with successive films of carbonate of baryta,' at last, nothing remains but pure water. The best way 1 prepare the hydrate of baryta in the pure state is to 10 some of the caustic baryta produced by the ignition o tho nitrate, in water, and to filter the solution whilstehosdrato filtrate is then allowed to cool, and the crystals ot Xitrate arc deposited. Some persons recommend mixing thsious to of baryta with its own weight of heavy spar, Prep, but heating it to redness. This prevents the frothing , Septi I is attent not any adding barium, ice-cold separate solution forms tn tain nin to the t and leav or two a crucible, baryta i as the a the pure and bee On this for carbc placed i. or three thick an lavrsa printing in the Ii asclearb in adop best pos most sui is deterr having be any d in theft tide the the ligh legativ Afticien paired otton v "J this Eives a s Chotogr & Che fraii Pfhersh Nt i 8 lbsrigh 2 pa i [1 Whe "resu oAdot inders thes 1 3," § 4
