THE idea is undoubtedly held among most amateur chemists and physicists that experiments with radium are inaccessible to those who' have only a limited fund for experimenting in this line. However, those who have a fair chemical equipment can prepare samples of fairly active material with little trouble and with which a great many interesting experiments can be performed. The radium in these samples is of course infinitesimal, but asserts its presence by ionizing gases and discharging electroscopes, and by blackening photographic plates through paper and sheets of wood and thin metal. In the separation of active material from pitchblende, samples of the ore which are known to be high in uranium should be taken as these always yield the most active substances. The ore is first reduced to a powder and roasted in a crucible for about 45 minutes and after cooling, pulverized to a fine powder. It is then mixed with about twice its weight of sodium carbonate and a little sodium nitrate and the mixture is again heated for nearly an hour. It is then extracted with water, and filtered and washed until all soluble parts are washed away. The insoluble portion is treated with a mixture of three parts C. P. sulphuric acid and one part C. P. nitric acid and this diluted with an equal amount of water. The acid should be added until effervescence ceases and until no more ore apparently goes into solution. The solution is then allowed to stand with occasional stirring for at least 24 hours. The insoluble part is allowed to settle and the acid solution decanted. If desired, this solution may be used for separation of the uranium contained in it. After decanting, the residue is thoroughly washed and treated in the same manner with an equal mixture of C. P. hydrochloric acid and water. This mixture which contains the polonium and actinium is then decanted and the residue washed and boiled with a saturated solution of sodium carbonate so as to change the still insoluble sulphates into carbonates. The sodium carbonate solution is drawn off and the residue washed and digested with pure hydrochloric acid diluted with a little water. This solution contains the active material which has now gone into solution. It is filtered and a slight excess of ammonia is added to the filtrate. Then it is again filtered and hydrogen sulphide gas is led into the clear solution until no more precipitation occurs. After filtering, sodium carbonate is added to the filtrate and the precipitate thus formed is thoroughly washed. Several grains of this mixture of active carbonates should be obtained from each ounce of ore. Enough dilute hydrobromic acid is added to dissolve the carbonates and the solution is filtered. C. P. sulphuric acid is added until the precipitation is complete when the precipitate is washed by decanting until all of the calcium sulphate in the sample is dissolved or until only a few grains remain (the quantity of barium sulphate being often very small if only three or four ounces of ore are used). This residue i;; converted into carbonates by boiling with sodium carbonate solution and this again is converted into bromides by a slight excess of C. P. hydrobromic acid. The solution is evaporated to dryness and is quickly transferred to glass stoppered bottles or is sealed into tubes. In this way a centigram or two of the radifer-ous calcium and barium bromides may be obtained from a pound of ore. However, if the quantity is very large and it is desired to obtain more active material this may be done by a series of crystallizations and recrystallizations until the desired activity is reached. The: radium bromide is less soluble than the barium salt, hence it crystallizes more quickly. The radiferous calcium and barium bromides obtained in this way are often self-luminous, the color of the phosphorescence varying with activity. The samples lose their phosphorescence if allowed to accumulate moisture but recover It again on being dried. If the samples are very active they will produce fluorescence in barium platinum cyanide and show the scintillations of the a rays when held close to a zinc sulphide screen and observed through a magnifying glass. Good radiographs can be taken in a few hours' time with a few grains of the impure RaBr, prepared in this manner, X-ray plates being the best to use for this purpose.
This article was originally published with the title "Preparation of Small Quantities of Impure Radium Bromide" in Scientific American 105, 25, 560 (December 1911)