The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Calcium, Chloride of                  Calculations and Constants
cent, by hot water; insoluble in alcohol and ether; it is soluble in water containing carbonic acid, a soluble salt, Ca(HCO)7, being formed. It is used for cleaning glass, in toning-baths, and for preparing other calcium salts.
Calcium, Chloride of (Ger., Calciumchlorid; Fr., Chlorure de calcium;. Ital., Cloruro di calcid). CaCl2=iii. Made by dissolving chalk in hydrochloric acid, and evaporating the solu-tion. One part is soluble in -25 parts of cold water and -15 of hot, in 7 parts of absolute alcohol. The salt is met with in two forms - as a crystalline substance and also in the form of white agglutinated masses. The latter form is used for the preservation of platinotype and other paper, and acts by absorption of the aqueous vapour from the air; and it will be found in time to become very moist, and, if left long enough, quite liquid. In either case it should be collected in a common jar or vessel, and placed in a hot oven, when the water absorbed will be driven off and the salt will be as good as new so far as its hygroscopic qualities go. The form of preservative box now most used is commonly called a Calcium Tube (q.v.).
Calcium Hydrate (Ger., Calciumhydroxid; Fr., Hydrate de chaux; Ital., Cake sfientd). Ca(OH)2 = 74. Synonyms : Calcium Hydroxide, Hydrate of Lime, Slaked Lime. Prepared by moistening quicklime with water. It is a white powder, and is soluble in 760 parts of cold water, less soluble in hot water; its solution is called lime-water.
Calcium Oxide. Ordinary quick lime. (See Lime Water.)
Calcium Tube or Box. This is usually a metal tube with, at one end, a separate chamber to contain Calcium Chloride (q.v.), and is used to prevent the action of moisture on certain papers, such as platinotype, etc. Another pattern, in the form of a box, was much used in the early days of photography under the name of Marion's Preservative Case. Carbon tissue, or sensitised albu-menised paper, may be kept for a 'long time in a perfectly dry atmosphere.
Calculations and Constants. Sufficient data for the most important photographic calculations will be found distributed under various headings, as Equivalence, Chemical; Hy-drometers AND HYDROMETRY, ANGLE OF VlEW, LENSES,
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