Lithium Bromide Litho-Photogravure
Lithium Bromide (Ger., BromHthtum, Lithhi?nbromid ; Fr. Bromure de lithine; Ital., Bromuro di litio.) LiBr = 87. This salt, which occurs in transparent white tablets or colourless needles which are very deliquescent, can be prepared by double decomposition of lithium sulphate and barium bromide. Solu-bility 143 per cent, in cold, 290 per cent, in hot, water. Very soluble in alcohol and ether. Sometimes used in collodion emulsion making.
Lithium Chloride (Ger., Chlorlithium% Lithiumchlorid; Fr., Chlorure de lithine; Ital., Cloruro di litio). LiCl,2H20 = 78*5. This can be prepared in a similar manner to the bromide salt. It occurs in octahedral crystals which are very deliquescent. Solubility 82 per cent, in cold, 146 per cent, in hot, water, soluble in alcohol and ether. It is used in the preparation of collodio-chloride emulsions.
Lithium Iodide (Ger., Iodlithium, Lithinmiodid; Fr., Iodure de lithine ; Ital., Iodnro di litid). Lil = 134. Made in a similar manner to the bromide salt. Occurs in yellowish crystals which are very deliquescent. Solubility, 100 per cent, in cold, 133 per cent, in hot water; freely soluble in alcohol. Used for iodising collodion.
Lithography, Photo-. A sheet of paper is coated with bichromated gelatine (see Carbon Processes ; also Anthrako-type), exposed under a negative, covered by a very thin film of printing-ink, and then soaked in water. The unexposed por-tions of the gelatine film will now swell, and the ink can be wiped off these parts by a tuft of cotton-wool, leaving an image on the paper which can be transferred to stone, and treated by ordinary lithographic methods. There are many modifications of the above, and also methods based on the use of sensitive bitumen. Sometimes a collotype print (see Collotype) is trans-ferred to the stone. Under Bibliography will be found the title of a special work on Collotype and Photolithography.
Litho-Photogravure. A method of Eckstein, in which the photolithographic transfer (see preceding article) is put down on a stone ruled with a system of very fine lines ; these serving to break up the gradations into a printing grain, and provide for the rendering or half-tone.