Positive Ionization from Hot Salts. 683 



same temperature, but no systematic attempt was made to 

 reduce it, as it was quite small compared with the effects 

 produced by all the salts investigated, with one exception. 



The experiments with the different salts will now be con- 

 sidered in the order in which they were carried out. In 

 every case current-E.M.F. curves were taken at three dif- 

 ferent pressures : (1) at the lowest pressure attainable by 

 working the Gaede pump continuously, usually about 

 0*004 mm., (2) at a pressure between 0*5 and 0*8 mm., and 

 (3) at a pressure between 5 and 10 mm. This was done 

 before the experiments on the variation with air pressure 

 were carried out, in order to make sure that there was 

 nothing exceptional about the relation between the current 

 and the voltage. The dependence upon pressure was ex- 

 amined under constant potentials of 40 and 160 volts 

 respectively, and in each case with both rising and falling 

 pressures. As a rule a series started w r ith the highest 

 attainable vacuum, so that the first observations were with 

 increasing pressures. 



Sodium Sulphate. — The current-E.M.F. curves were so 

 similar to those with the empty tube as to call for no special 

 description. In this case the current-pressure curves were 

 taken by starting from the highest pressures. The stead v 

 values with + 40 volts applied P.D. are given in the following 

 table in the order in which they were taken. 



Pressure (mm.) 8"9 33 l'l '38 '14 -033 -006 -0048 



Current 42 39 33 26"8 25 24 24 ~4* 



(l=l-25xl0" 8 amp.) 



Actual Temperature, 797 ... 795 



degrees centigrade. 



Pressure '004 -037 '064 1-2 -50 -93 16 7"6 



Current 28 28-5 29 30 36"5 44 52 56 



Actual temperature... 797 ... 799 



The general course of the readings with -f- 160 volts was quite 

 similar, namely, 



Pressure 7*8 6-1 4'25 3'15 2'2 1-36 -90 '40 '10 -006 



Current 36'9 35-2 32*2 28'2 24-4 203 17'2 13'7 13'2 12'0 



Actual temperature ... 783 779 774 



Pressure... '005 '033 '22 -68 11 1-6 2'5 33 5*2 65 8'1 

 Current... 116 11'5 113 131 14'6 15'6 16*7 156 15'5 15"1 14-5 



Actual tern- 767 734 728 720 



perature 



* Reading rose slowly from 24 to 2 



