February 2, 1917] 



SCIENCE 



123 



large number of tests were made using lead 

 nitrate crystals with 7-ray sources varying 

 from 200 to 14 millicuries of radium emana- 

 tion, the source and crystals being placed at 

 different distances from the chamber A. The 

 sensibility of the electroscope was also varied 

 over a wide range. 



Table I. gives a summary of the results ob- 

 tained for six separate experiments with lead 

 nitrate. 



The percentage of total beam absorbed was 

 obtained by dividing the total change in ab- 

 sorption from crystalline to non-crystalline 

 state by the leak due to the entire cone of 

 rays measured by connecting chamber B alone 

 to the electroscope. For the above experi- 

 ments in which a layer of lead nitrate crystals 

 3.4 cm. thick was used, with the 14 mg. stand- 

 ard as source of rays, this reading was 415 

 divisions per min. 



A detailed study of the effect was made using 

 7-ray sources varying from 200 to 14 milli- 

 curies of radium emanation, the source and 

 crystals being placed at different distances 

 from the chamber A. The sensibility of the 

 electroscope was also varied over a wide range. 



Table II. gives a summary of results obtained 

 for a number of crystalline materials. 



Since the size of the crystals differed greatly 

 and other conditions of experiment were not 

 the same in all cases, it is not possible to at- 

 tempt any quantitative comparison of these 

 results. They are inserted as an indication of 

 the order of the effects observed. 



EXPERIMENTS WITH CRYSTALLINE MERCURY 



A more direct method would be to note the 

 relative 7-ray absorption for some substance 

 which could easily be obtained in crystalline 

 and non-crystalline states. Water and mer- 

 cury satisfy these conditions. Owing to the 

 large density of the latter, it should produce a 

 good deal of 7-ray scattering, and since it melts 

 rapidly the sensibility of the electroscope would 

 not alter appreciably during an experiment. 

 The radiation entering the balance chamber 

 was adjusted so as to give a very slow rate of 

 leak of the electroscope for a given weight of 

 mercury. The mercury was then removed and 

 solidified in a Dewar vessel by the use of car- 

 bon-dioxide snow. The rates of leak with the 

 solid mercury were then measured and obser- 

 vations taken as melting proceeded. More 

 than 40 separate tests were made under widely 

 varying experimental conditions, but while the 

 data in general showed a small decrease in ab- 

 sorption for the fluid state, it was in most 

 cases little more than the experimental error. 

 The crystals obtained in every case were very 

 minute. 



SOLUTION EXPERIMENTS 



A number of attempts were made to note a 

 change in absorption for lead nitrate entering 

 into solution. Other soluble crystalline sub- 

 stances were also tried including salt, sugar, 

 etc. A large crystallizing dish containing 600 



