428 



NATURE 



[October b, 1910 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opiniorts 

 expressed by lus correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. \ 



The Fur Trade. 



It is recorded in the " Life of Professor Owen " that on 

 one occasion Lord John Russell sent him a bone, request- 

 ing that it might be identified. Owen replied that it was 

 an ordinary ham-bone, pertaining to the genus Sus, and 

 was informed that Lord John had received from President 

 Grant what purported to be a bear's ham, concerning 

 which he had his doubts, hence the inquiry. 



It is not improbabje that naturalists are occasionally 

 appealed to in a similar manner for judgments on the 

 identity of furs. In these circumstances, they may well 

 be excused if they lack Prof. Owen's assurance, or are 

 found entirely wrong. The mysteries of the fur trade are 

 surely beyond the understanding of even a skilled zoologist ; 

 but there is an American publication in which they are 

 revealed to the astonished reader. This is the retail 

 catalogue of .=\lbrecht and Son, of Minnesota. This firm 

 does a very large business, and has no wish to deceive its 

 customers as to the nature of their purchases, and yet 

 cannot get away from the current trade names. Conse- 

 quently, it publishes a detailed synonymy, some of which 

 has not yet found its way into zoological works. I 

 venture to extract a few items for the instruction and 

 entertainment of those who have not access to the 

 catalogue. 



.ilaska Bear. — " The best Minnesota Raccoon, coloured 

 a dark brown." 



.Adelaide Chinchilla. — .Australian Opossum. 



French Ermine. — " .Made from selected skins of the 

 French Coney." 



Baltic (White) fcv.— " The fur of the large Hare of 

 northern Europe." 



Iceland While Fo.\:. — " White Thibet Lamb, combed 

 until the hair is straight." 



Kamtschatka Fo.\. — " Trade name of the northern 

 Timber Wolf." 



Baltic Lynx. — " This fur is secured from the large 

 Belgian Hare of northern Europe, dyed a jet black." 



Finland Lynx. — Australian Wallaby. 



Natural Black Marten. — " From the black Marten 

 (commonly known as skunk)." 



Russian Marten. — .American Opossum. 



Russian Mink. — Mongolian Marmot. 



.Siberian Pony. — Russian Calf. 



Inland Seal. — French Coney. 



Coast Seal. — " Albrecht coast seal is made from the 

 skins of the French Coney." 



But the catalogue itself should be in every zoological 

 library. It contains other items of interest ; thus it 

 appears that one may spend the trifling sum of 625 

 dollars on a muff made of Russian sable. Single skins 

 •of this animal are valued as high as 500 dollars when of 

 the best quality. T. D. .\. Cockerell. 



LTniversitv of Colorado, September 11. 



An Attempt to Determine the Supposed Change in 

 Weight Accompanying the Radio-active Disinte- 

 gration of Radium. 



Some time ago Mr. Grant and I designed and constructed 

 -a micro-balance (Proc. Royal Society, A, vol. Ixxxii., 

 p. 580) for the purpose of demonstrating, if possible, the 

 occurrence of a change in weight accompanying the radio- 

 active disintegration of radium. 



We have recently been attempting to do this, using 

 7-5 milligrams of pure radium bromide. It was necessary 

 to have two balances of great sensitiveness in order to 

 carry out our proposed experiment, and tlie two balances 

 ■which we have used have each a sensitiveness of 2-5x10-° 

 ■grams, and for both of them the resting point has not 

 varied by more than 5x10-' gram during several periods 

 of observation varying in length from a week to a month. 



NO. 2136, VOL. 84] 



The plan of our proposed experiment was as follows. 

 The two balances were mounted side by side in the same 

 balance case in such a way that the images of a fine 

 illuminated slit could be reflected on to the same scale 

 from the mirrors on the two balances. 



One of the balances was to serve as a check on the 

 second, which was to be used to determine the weight of 

 the active deposit from the radium. This second balance 

 was of the type B figured in our paper {loc. cit.), and was 

 provided with a fine fibre attachment and quartz hook 

 from which could be suspended a piece of fine platinum 

 wire. 



A piece of stout platinum wire was passed through the 

 wall of the balance case, and well insulated from it, and 

 by a mechanical contrivance this insulated wire could be 

 brought, when desired, into contact with the wire suspended 

 from one end of the balance beam. By means of this 

 second wire the suspended wire could be raised to a 

 negative potential of five hundred volts. 



Through the wall of the balance case were also passed 

 two glass tubes leading to an air-circulating apparatus 

 and to a bubbler containing the solution of radium 

 bromide. 



By means of this circulating apparatus the air con- 

 tained in the balance case could be bubbled continuously 

 through the radium bromide solution, thus keeping it 

 charged with the radium emanation. As this decayed into 

 radium A, the latter in the electric field should be driven 

 to the charged and counterpoised platinum wire and 

 accumulated there, and so its weight determined. 



The behaviour of the balance was investigated with the 

 greatest care, and after many disturbing effects had been 

 discovered and eliminated one at a time, it was finally 

 shown that the resting point of both balances was constant 

 for at least a month, when every condition was the same 

 as for the actual experiment with the single exception that 

 the bubbler contained water instead of the radium bromide 

 solution. Thus the following changes in conditions did 

 not affect the resting point by more than 5-0x10-' 

 gram : — (a) Releasing and arresting the balance beam ; 

 (b) touching and jerking the suspended platinum wire; 

 ((■) starting and stopping the circulation of the air ; 

 (d) charging and discharging the platinum wire. 



The experiment was then started by replacing the water 

 in the bubbler by the solution of radium bromide and the 

 behaviour of the balance again tested, when it was found 

 that the resting point was still unaffected by the opera- 

 tions (a), (b), and (c). 



The wire was then charged, and it was expected that 

 this would cause an increase in weight of the order of 

 10X10-' gram per day, but instead of this an increase 

 of weight of about 30X10-' gram has been found to 

 occur. 



Whilst it is not impossible that this increase in weight 

 is due to radio-active changes, it is so much greater than 

 that calculated on the basis of the electrical evidence 

 that the conditions of the experiment require to be re- 

 examined with the greatest care. An explanation that 

 suggests itself to us is the following. With the balance 

 case used by us and described in our paper (.loc. cit.) the 

 ground joints and flange are necessarily made vacuum 

 tight by some form of lubricant. We have used the so- 

 called rubber grease, which probably distributes vapour 

 of heavy molecular weight throughout the balance case, 

 although its vapour pressure is far too small to be detected 

 bv ordinary methods. 



It is possible that the ions produced by the emanation 

 and its radio-active products form nuclei for the con- 

 densation of this vapour, and that these condensed aggre- 

 gates are driven with the charged nuclei to the charged 

 and counterpoised platinum wire, there accumulated, and 

 weighed. 



The balance case and other apparatus employed is being 

 modified so as to exclude all possibility of condensation 

 of vapour, and it is hoped, when the necessary preliminary 

 study of the behaviour of the instruments has been carried 

 out, to determine whether the large change in weight that 

 has been observed is an accompaniment of the radio- 

 active process or an adventitious effect. 



Bertram D. Steele. 

 The Universitv, Melbourne. 



