December 3, 1908] 



NA TURE 



129 



But since the students to be educated at Finsbury were 

 largely of the higher artisan class, or at any rate were 

 already familiar with machinery, perhaps I should rather 

 put the matter conversely, and say that the object aimed 

 at was to coax their already too material and concrete 

 ideas towards something more generalised and abstract, by 

 analysing into simplicity the complex machines with w-hich 

 many of them in their daily life had to deal, thus assisting 

 them to grasp something of the theoretical physical prin- 

 ciples underlying them all. 



An admirable object, excellently carried out ! Not a 

 word have I to say towards minimising it : only do not 

 I'jt us minimise the work of others either. 



November 21. Oliviir Lodge. 



Apparent Decay of Radium. 



I WISH to put on record an observation relating to the 

 amount of " electrolytic gas " obtainable from a solution 

 of radium bromide. Some four years ago, about 172 milli- 

 grams of radium salts, of which 152 were bromide and 

 10 sulphate, were enclosed in four small bulbs along with 

 water, which dissolved the bromide, and in vi'hich the 

 sulphate was suspended. These bulbs were sealed to a 

 small Topler pump, and for three years the mixed oxygen 

 and hydrogen gases were pumped off at short intervals — 

 about four days between two extractions. With the 

 emanation accompanying this mixture various experiments 

 were performed, an account of which has appeared in the 

 Troceedings of the Royal Society and the Transactions of 

 (he Chemical Society. 



In November, 1907, I received from the Vienna Academy 

 what was supposed to be 0-5 gram of pure radium bromide ; 

 I was told that that was its weight in 1905. It weighed 

 on receipt only 0-388 gram. This substance was washed 

 into a bulb, and sealed to the pump, along with the other 

 bulbs. The amount of gas collected from the larger 

 quantity, however, did not appear to be proportional to 

 its greater weight, and as analysis of a sample showed 

 that it consisted largely of carbonate, insoluble in water, 

 it was resolved to convert the carbonate into bromide by 

 introducing into the bulb with a pipette some pure hydro- 

 bromic acid. (I may mention, parenthetically, that the 

 small sample, converted into bromide, gained in weight 

 to such an extent as to show that the original amount 

 must have weighed 04971 gram, as RdBr„,2H,0.) The 

 gas pumped off after this addition of hydrobromic acid 

 contained much free bromine, but after a fevir weeks the 

 evolution of bromine ceased, and*' electrolytic gas " was pro- 

 duced to the amount of about 30 c.c. a week, always mixed 

 with a small excess of hydrogen. This regular evolution 



mtinuc-d from February until November 11. On that 

 ' iv the usual 30 c.c. of gas were pumped off; I have 

 .1 note that " an unusually small quantity of hydrogen 

 remained after explosion." On November 18 the gas 

 was again pumped off ; the quantity was approximately 

 13 c.c. .Although it appeared unlikely that the tubes and 

 taps should have been blocked, it was still possible. On 

 November 25 the gas was again removed ; its volume was 

 about 15 c.c. At this stage air was admitted into the 

 pump and the connected bulbs, and it was proved that 

 there had been no stoppage. -Advantage was taken of this 

 to clean the pump and the connecting tubes, and to re- 

 grease the stop-cocks. The air was then removed com- 

 pletely by pumping. To-day (November 30) the gas was 

 again pumped off ; its volume was about 0-5 c.c. It still 

 • \|i!oded, and left about half its volume of excess hydrogen. 

 Two alternative suppositions suggest themselves : — 

 ither the radium bromide, of which the apparatus contains 

 0-5071 gram, implying 0-2716 gram of metallic radium, has 

 practically ceased to decompose water (about 25 c.c. of 

 solution are present in the bulbs), or the reverse reaction, 

 \\7-. the velocity of combination of oxygen and hydrogen 



I form water, has increased to such ah extent as to reverse 

 \\i- decomposition. 



It has been assumed that the life-period of radium is 

 very long, say 2000 years, although Mr. Cameron and I, 

 by measuring what we believe to be the true volume of 

 the emanation, arrived at a considerably shorter period. 

 Here, however, appears to be, on the first alternative, a 

 proof that one of the ways in which the radium expends 

 at least a portion of its energy has been stopped. It would 

 be interesting to know if the other ways, say the evolution 



NO. 2040, VOL. 79] 



of heat or the emission of " rays," are similarly affected 

 by time. Willia.m R.i^ms.iy. 



University College, November 30. 



Production of Helitm from Uranium. 



In a paper in the October number of the Philosophical 

 Magazine of this year I gave a preliminary account of 

 some attempts to detect and measure the production of 

 helium from the primary radio-elements, on w'hich I have 

 been engaged since 1905. The results given were few, 

 and referred mainly to the element thorium. The follow- 

 ing further results, obtained since the publication of the 

 paper, with the element uranium carry the subject a stage 

 further. The method is described in detail in the paper 

 referred to. By spe-cial arrangements the solutions of the 

 substances employed can be freed absolutely from air, and 

 maintained in this condition indefinitely. .After any 

 desired period of accumulation the gases can be completely 

 expelled by boiling the solution in a stream of gas from 

 a voltameter. The expelled gases are freed from water 

 by cooling, and then subjected to the action of the vapour 

 of calcium in a special vacuum furnace, whereby all but 

 the inert gases are perfectly absorbed. .After cooling the 

 furnace is filled with mercury, and the residual gas, if 

 any, compressed into the smallest possible spectrum tube 

 of lead glass. The minimum quantity of helium detect- 

 able in a successful experiment has been found by re- 

 peated trial to be 2x10-'° gram. Blank tests with a 

 similar apparatus containing sodium sulphate solution were 

 performed, and I feel confident that the data obtained are 

 trustworthy. 



I have used two separate quantities of uranium nitrate. 

 The first and smaller had been carefully purified by Mr. 

 T. D. Mackenzie by extraction with ether. It contained 

 340 grams of the element uranium. When it became 

 evident that the rate of production was too slow to be 

 conveniently estimated with this quantity, a second ex- 

 periment on a much larger scale was started. The cost 

 of this and similar other large-scale experiments was 

 defrayed by a research grant from the Carnegie trustees. 

 Four kilograms of uranium nitrate of good commercial 

 quality, which had been re-crystallised from water, were 

 employed. It contained 1S50 grams of uranium. The 

 preparation of the experiment and complete removal of 

 air were effected by .August 15 of this year. The first test 

 for helium was performed after a period of sixty-one days. 

 Helium in several times the minimum quantity detectable 

 by the method employed was proved to be present in the 

 extracted gases. The second test was performed after a 

 period of twenty-seven days. Helium was again present, 

 this time in quantity not much, if any, greater than the 

 minimum detectable. The next test was performed after 

 twelve days. No helium could be detected, although the 

 experiment was a singularly perfect one. An experiment 

 was then performed with the smaller quantity of uranium 

 after a period of accumulation of 128 days. Helium was 

 clearly detected, and its quantity estimated to be not 

 greater than 1-5 times the minimum quantity. 



The production of helium from uranium may therefore 

 be considered to be established. With regard to the rate 

 of production, the experiments show that this cannot be 

 far from 2 X io-''(year)-'. That is to say, about 2 milli- 

 grams of helium are formed per year per million kilo- 

 grams of uranium. The second test referred to shows 

 "tfiat the rate is not less than 1-5. The third test shows 

 that it is less than 3-3. The last test with the smaller 

 quantity shows that the rate is not less than 1-7, and prob- 

 ably not greater than 2-5. It is of interest to note that 

 the theoretical rate of production I recently calculated from 

 the disintegration theory is 2 X lo-'-(year)-', on the 

 assumption that one atom of uranium produced but one 

 atom of helium. These measurements, therefore, lend no 

 support to the view, discussed in the paper referred to, that 

 uranium on disintegration expels two lielium atoms. 



I may mention that I have commenced the observation 

 of a quantity of sylvine (potassium chloride), one of the 

 minerals investigated by Strutt, and regarded by him as 

 exceptional in containing helium which cannot be ascribed 

 to known radio-active changes. The tests so far indicate 

 that the rate of production of helium from this substance, 

 if anv, is below 2-5 X 10- '"(year)-'. 



L'nivcrsitv of Glasgow. Frederick Soddv. 



