IODIDE OF CALCIUM. Ca. 1=146. This salt is obtained by dissolving carbonate of lime in hydriodic acid, evaporating to dryness, and fusing the residue, in a close vessel. When this is dissolved in water and evaporated, it furnishes white deliquescent crystals.
The nitrate of lime formed in the nitrate bath when this iodizer is employed is a very deliquescent salt, and would therefore tend to preserve the moisture of the excited film. The deliquescent pro perties of the iodide and nitrate of lime recommend this iodizer for use, although it is not much employed.
Iodide of calcium is extremely soluble in water, and alcohol, even when absolute. The alcoholic solution is discoloured by light, and collodion iodized with it becomes gradually reddened, as with the potassium salt. It gives excellent negatives, remarkable for their cleanness and density.
!!!P to r or Tam There are two iodides of iron, viz. a prot !• FP. I, and a periodide, the exact composition of which has t been ascertained.
Protiodide of iron is formed by digesting iron filings or iron ! !re in water with iodine, the metal being in excess. A greenish
I a ion is obtained, to which sugar is sometimes added for medicinal purposes. It is extremely unstable, and throws down oxide of iron b? exposure to air. On evaporation it yields a grey fusible salt, hieh is soluble in alcohol, the solution being rapidly decomposed light.
When protiodide of iron is used as an iodizer in photography, protonitrate of iron is formed in the nitrate bath, and also in the ,,nsitive film. This acts as a developer, and speedily blackens and •poils the bath ; it also developes the image so long as the plate or paper continues moist ; the picture, therefore, comes out after exposure, by a sort of self-developing process. In consequence of this property of iodide of iron as an iodizer, it has been thought to Erive extraordinary sensitiveness to collodion, but that opinion is erroneous.