"Take of bromine, two ounces; carbonate of potassa, two ounces and a drachm; filings of iron, one ounce; distilled water, three pints. Add first the iron, and afterwards the bromine, to a pint and a half of the distilled water. Set aside the mixture for half an hour, frequently stirring it with a spatula. Apply to it a gentle heat, and when a greenish colour appears, add the carbonate of potassa dissolved in the remainder of the water. Strain and wash the residue with two pints of boiling distilled water, and again strain. Evaporate the mixed solutions, that crystals may be formed."

This process comprehends two distinct stages: first, the combination of the bromine with the iron, which readily takes place at a slightly elevated temperature; secondly, the decomposition of the bromide of iron by the potassa. In this stage of the process, the oxygen of the potassa unites with the iron, and converts it into a protoxide which readily combines with the carbonic acid, also separated from the potassa, and forms a carbonate of iron, which, being insoluble, falls to the bottom of the vessel, whilst the bromide of potassium, produced by the union of the free bromine with the potassium, remains in solution. It readily crystallizes by evaporation.

Qualities. - Bromide of potassium is a white, inodorous, cubical salt, in quadrangular prismatic crystals, which decrepitate: it is very soluble in water, but only slightly so in alcohol. It consists of 66.1 parts of bromine+ 33.9 of potassium, in 100 parts, or of 1 eq. of bromine = 78.4 + 1 of potassium = 39.15; making the equivalent = 117.55. It is incompatible with acids, metallic salts, and chlorine.

Medical properties and uses. - This bromide is stimulant and powerfully deobstruent, acting on the glandular system in the same manner as the iodide of potassium. It has been much employed on the Continent, especially by Majendie, and in this country by Dr. Williams of St. Thomas's Hospital, in enlargement of the spleen. It is said that, after ascertaining the extent of the enlargement by percussion, and marking it on the skin with ink, the daily diminution may be readily observed. I have found it servicable in improving the secretion of the liver. The dose is from gr. iij. to gr. x. twice or thrice a day.

Potassii Iodidum. Lond, Iodide of Potassium

"Take of iodine, six ounces; carbonate of potassa, four ounces; iron filings, two ounces; distilled water, six pints. Put the iodine into four pints of the water, and add to it the iron, now and then stirring with a spatula for half an hour. Apply a gentle heat; and when the mixture acquires a greenish colour, add to it the carbonate of potassa dissolved in two pints of water, and filter. Wash the residue in two pints of boiling distilled water, and again filter. Evaporate the mixed solutions, that crystals may be formed."

In this process, the same changes, which I have described as occurring in the process for the bromide of potassium, take place.