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SCIENCE 



[N. S. Vol. XXXII. No. 831 



mends that the name " Curie " be given to the 

 quantity or mass of emanation in equilibrium 

 with one gram of radium (element). The 

 millicurie would thus be the amount of ema- 

 nation in equilibrium with one milligram of 

 radium. 



6. The question of proposing special names 

 for units of measurement of minute quanti- 

 ties of radium and its emanation is under 

 consideration, but no definite conclusions 

 have as yet been reached. 



7. As some members of the com m ittee are 

 not present at the Brussels Congress, and as 

 it has not been possible to obtain informa- 

 tion as to their views on these questions, the 

 recommendations here made are not neces- 

 sarily final. The committee reserves the 

 power to modify them if on further considera- 

 tion this appears to be desirable. 



The preparation of a standard specimen of 

 a pure radium salt is thus assured. The com- 

 mittee was fully agreed that by placing the 

 matter in the hands of Mme. Curie the most 

 satisfactory and trustworthy results could be 

 attained. Mme. Curie has accepted the full 

 responsibility and this portion of the work 

 will be entirely under her personal charge. 

 The methods which will be used by her are 

 left entirely to her discretion. It will be 

 necessary for the committee to approach their 

 several governments or the scientific societies 

 of the different countries interested to secure 

 the funds necessary to defray the cost of the 

 primary standard, which at the present price 

 of radium will probably be about $2,500. It 

 may at first sight appear that the amount of 

 radium in the primary standard, viz., about 

 20 mg., is unnecessarily large, but it was 

 pointed out by Mme. Curie that the accurate 

 weighing of quantities less than the amount 

 mentioned of such a relatively unstable salt 

 as anhydrous radium chloride could not be 

 satisfactorily accomplished. The later or 

 secondary standards will be calibrated by com- 

 parison with the primary standard, making 

 use of the y radiation emitted by the radium 

 salts. It will probably be possible to do this 

 satisfactorily if the secondary standards con- 

 tain a somewhat smaller amount of radium 



than the primary. It is anticipated that 

 about 10 milligrams of radium will be a sufii- 

 cient amount for a secondary standard. 

 These secondary standards will be compared 

 as stated with the primary and also with one 

 another, before their distribution, and it will 

 thus be possible for each country to have in 

 its possession, and at its disposal, one of the 

 secondary standards which may be used for the 

 measurement and certification of quantities 

 of radium when desired. The advantages of 

 this arrangement would seem to be clearly ap- 

 parent. Not only will it be possible for the 

 scientific results obtained in the subject of 

 radioactivity in different countries to be 

 brought into complete accord, but individuals 

 interested in either the sale or purchase of 

 specimens of radium salts can then be able to 

 obtain trustworthy data as to the amounts of 

 radium in the specimens involved in the 

 transaction. Great uncertainty has existed in 

 the past in the latter cases. Many people 

 have made purchases at high prices only to 

 discover later that the radium salts which 

 they had bought were far from pure. As 

 probably more than $500,000 worth of radium 

 preparations have already been sold in this 

 country it will be seen that some definite 

 standard of quality and value is imperative 

 for the protection of all concerned. 



The problem of the preparation of small 

 substandards containing one or two milli- 

 grams of radium, suitable for the use of most 

 scientific laboratories, is one of the most diffi- 

 cult which the committee has to consider. 

 By means of the y radiation it is not difficult, 

 with proper precautions, to compare approxi- 

 mately equal quantities of radium with an 

 error of considerably less than one per cent. 

 But when the amounts of radium to be com- 

 pared differ by a ratio of ten to one the prob- 

 lem is much more complicated. As attention 

 will now be devoted to this matter, it is prob- 

 able, however, that methods will be devised 

 for conducting comparisons of this sort with 

 the degree of accuracy required and to cali- 

 brate the smaller substandards by direct com- 

 parison with the primary standard or, at all 

 events, with the national standards of approxi- 



