TRANSACTIONS OF SECTION B. 



601 



phenomenon, possessed T^y many bodies in less degree, led the author to select it 

 from amongst bodies whose colour changes with heat, to verify one point of the 

 electro-magnetic theory of light. According to that theory, all good conductors of 

 electricity should he opaque to light ; and therefore, if this theory holds good, the 

 increase of opacity and of light-absorbing power by a body should indicate that its 

 electrical conductivity was increasing. To put this to the test the author has 

 measured the conducting power of the iodide at various temperatures. This was 

 done by placing a film of the iodide about 1 millimetre thick between two plates of 

 platinised lead, each 10 centimetres square, and determining its resistance in a 

 Wheatstone's bridge at different temperatures. A decrease was observed from 

 40° C. up to about 110° C, at which the resistance began again to increase. The 

 author believes this increase to be due to dissociation setting in, as at about 150° C. 

 it is decomposed, mercuric iodide subliming away and leaving pale brown cuprous 

 iodide behind. The greatest change of resistance was between 65° 0. and 90° 0. 

 with rising temperattu-es, and between 95° C. and 75° 0. with falling temperatures. 

 In both cases tlie maximum rate of increase of conductivity was between 87'5° and 

 88"5° C, precisely the temperature at which the rate of change of tint is also a 

 maximum. The specific electric conductivity doubles between 82° and 92°. The 

 following values of Xt tbe specific electric conductivity, were obtained : — 



At50°C. X = 2-396 x lO-s 



82° =-- 9-865 X 10-8 



92° = 18-64 X 10-3 



109° = 23-95 X 10-8 



The maximum value of ^ was 0*221 x 10-'^. 

 dd 



These results were therefore held to support the theory, though experiments on 

 other bodies exhibiting similar phenomena were to be desired in confirmation, before 

 any sweeping generalisation would be admissible. 



The author pointed out, in conclusion, that the remarkable change of colour 

 exhibited by this body rendered it a valuable thermoscope for lecture purposes. He 

 had employed it for demonstrating to an audience the heating effects of absorption 

 of radiation, the conductivity of heat in crystals, and the heat produced by 

 magnetic and mechanical friction. 



7. Analyses of the Water and Gas from Blowing Wells near Northallerton. 



By T. Fairlet, F.B.S.E. 



The wells are three in number : — Well at Solberge, 3^ miles S. from Northal- 

 lerton ; well at Langton, about 4 nules W.N.W. from Northallerton ; and well at 

 Omhams, 2 miles S. from Boroughbridge. In each of these currents of air ilow 

 from the shafts of the wells during a falling period of the barometer, and inward 

 currents flow into the shafts while the barometer is rising. When the rise or fall 

 is considerable the currents are very powerful, causing a strong draught or wind 

 in the openings leading to the shaft. 



The well at Solberge is situated on Mr. Hutton's estate near his residence. 

 Through this gentleman's kindness and assistance the author was able to make a 

 number of experiments. A number of analyses of the gas from the out-current 

 showed it to be common air containing 20'9 per cent, of oxygen. Analyses of the 

 water gave the results (grains per gallon) : — 



Chloride of sodium . . . 4-1 



Hardness before boiling, 326° 



after boiling, 8-4° 



Total solids by evaporation 



38-64 



