1922.) Indian Science Congress. 1.8.C. 55 
sey the elements they had chosen possessed high ionisation potentials, 
could not penta be ionised to any appreciable extent at the tem- 
ciatieos ~ 
The author Pad preci ously given a theoretical ireatment of the prob- 
lem in several nome: egg caiy in the Phil. Mag. 1920 and 1921, in which 
it was shown n factor in determining rani io was the 
ionisation tiated yee siete as deduced from the quantum law 
whe 
quency of the pict series of the acs ent. The less was the 
tion-potential, the greater is the ease with which it can "be 4 his "The e 
fraction x of atoms ionised under the pressure P, and terapeagicis T is 
given by the Naenat formu me 
U 
ee eee log T—6°5. 
lot Tag P= gy arts ie 
Where U is the heat of ionisation, and connected with V by the 

eVN ; 
rel I a A J b T h leanivalent 
elation U 3007 where N 2 q 
of heat. 
Te i pips that of all elements caesium has the lowest ionisation 
potential, ai; 83 volts), the next in order being #b, and K. The 
author Taal tried the ex periment with Cs. The heating vessel was & 
g 
rature. A piece of Cs, Rb, or K was dropped from vst top into the 
furnace. The metal vaporised, ee aeplaned H,. The furnace contain- 
ing ionised caesium can be regarded as an electro! vet “als, with the 
plasini tube as one pester, and the thermocouple as he other elec- 
trode. pote iene of 1 to 6 volts wa 3 laid between the oh aera = 
and the thermocouple, with a calibrated milliamperem 
The deflections of the milliamperemeter directly gave the goer lees of 
the cell. 
It was verified that with pure hydrogen or ed air, there is no trace 
of conductivity in the cell. as , Rb or K was dropped 
into the furnace, a huge conductivity was obtai ned. With caesium, at 
1250 ili 
°C a current of 3 milliampe btained under a potential differ- 
ence of | vo specific resistance of t ) mid oo 
ohms be conductivit with decreasin; ‘ 
00°C. Under the same ried ta60 50°C) the 
was not detectable below 8 
resistances of Rb, K vapour were found to be about twice and four- 
times that of Cs vapour. 
results me in accordance with the author’s theory and ooo 
The 
believed to be the first experimental demonstration that gases can 
made conducting by heat alone. 
Further Notes on weiss designed Physical Apparatus.~— 
N. Mairra 
tains unt of a number of demonstration appa- 
ty oe nok previous communication was sent to 
gress mbay. 
The following have been added since ae 
No. l. Sliding Thermoscope for seins temperature gradien 
along a bar heated at one end. 3 
