Symbol, Br. Atomic weight, 78. This elementary substance is obtained from the uncrystallizable residuum of sea-water, termed _bittern_. It exists in the water in very minute proportion, combined with magnesium in the form of a soluble bromide of magnesium. _Properties._--Bromine is a deep reddish-brown liquid of a disagreeable odor, and fuming strongly at common temperatures; sparingly soluble in water (1 part in 23, Lowig), but more abundantly so in alcohol, and especially in ether. It is very heavy, having a specific gravity of 3·0. Bromine is closely analogous to chlorine and iodine in its chemical properties. It stands on the list intermediately between the two; its affinities being stronger than those of iodine, but weaker than chlorine. (_See_ chlorine.) It forms a large class of salts, of which the bromides of potassium, cadmium, and silver are the most familiar to photographers. Bromide of Potassium. Symbol, KBr. Atomic weight, 118. Bromide of potassium is prepared by adding bromine to caustic potash, and heating the product, which is a mixture of bromide of potassium and bromate of potash, to redness, in order to drive off the oxygen from the latter salt. It crystallizes in anhydrous cubes, like the chloride, and iodide, of potassium; it is easily soluble in water, but more sparingly so in alcohol; it yields red fumes of bromine when acted upon by sulphuric acid. Bromide of Silver. (_See_ Silver, Bromide of.) Carbonate of Soda. Symbol, NaO CO{2} + 10 Aq. This salt was formerly obtained from the ashes of seaweeds, but is now more economically manufactured on a large scale from common salt. The chloride of sodium is first converted into sulphate of soda, and afterwards the sulphate into carbonate of soda. _Properties._--The perfect crystals contain ten atoms of water, which are driven off by the application of heat, leaving a white powder--the anhydrous carbonate. _Common washing soda_ is a neutral carbonate, contaminated to a certain extent with chloride of sodium and sulphate of soda. The carbonate used for effervescing draughts is either a bicarbonate with 1 atom of water, or a sesquicarbonate, containing about 40 per cent, of real alkali; it is therefore nearly double as strong as the washing carbonate, which contains about 22 per cent, of soda. Carbonate of soda is soluble in twice its weight of water at 60°, the solution being strongly alkaline. Carbonate of Potash. (_See_ Potash, Carbonate of.) Caseine. (_See_ Milk.) Charcoal, Animal.