148 Report S.A.A. Advancement of Science. 



§4. Electrification of gases at temperatures below 400°C. 



In the experiments now to be described, the outstanding dififer- 

 ence is the temperature at which the results are produced. 



No attempt was made to determine the temperature accurately. 

 The highest temperature attained was about 35o°C, the melting 

 point of zinc. The effect of heating to a temperature slightly lower 

 than this was tried with a great many substances and combinations 

 of substances. 



The substances may be divided into two classes: (i) those 

 which, when heated, in certain circumstances, acquire the power of 

 giving a charge to the surrounding air; (2) those which, in like cir- 

 cumstances, do not acquire this power. The first class may be 

 sub-divided into (a) those in which it was possible to predict what 

 would happen, and (b) those in which it was not possible to predict. 



In class (b) is potassium permanganate. This substance was 

 tried several times with the first experimental arrangement. There 

 was always evidence that a gas was being given off in the back 

 pressure in the wash-bottles. When the air from the room was 

 drawn through while the tube was being heated, it was found that 

 the charge given tO' the filter (F,.) was sometimes positive and some- 

 times negative. Usually it was possible in the early part of the 

 experiment to influence the charge given to the filter by giving a 

 charge of a definite kind to the insulated axial wire ; for example, 

 in one experiment with the wire joined to the negative terminal of 

 a battery of 40 Leclanche's, the electrification given to the filter was 

 positive, to the positive terminal it was negative. As the tempera- 

 ture rose, the positive reading became less and less, till, finally, in 

 all cases, the electrification given to the filter (Fe) was negative. 



A second substance behaving in a very erratic manner was zinc 

 chloride. Some days the results were negative, on others positive. 

 Consistent results were obtained with potassium bichromate, treated 

 with iodine or with bromine, on a zinc strip placed in a zinc tube ; 

 with common salt similarly treated, with lithium chloride under 

 like conditions, with potassium iodide treated with bromine, and 

 with zinc sulphide alone. No electrification of the atmosphere was 

 obtained in the case of potassium bichromate, common salt, lithium 

 chloride, treated with iodine or with bromine, in the absence of zinc. 

 The effect of the absence of zinc in the case of potassium iodide 

 treated with bromine was not tried. Zinc sulphide was not tried in 

 the absence of zinc. 



The substances of the second class, i.e., those which, when 

 heated, showed no electrification of the surrounding atmosphere, 

 were barium sulphide, either alone or after being treated with iodine 

 and heated in an iron tube, barium oxide and barium peroxide 

 heated in an iron tube, copper oxide heated in an iron tube, copper 

 sulphide similarly heated, potassium carbonate with or without 

 iodine in a zinc tube, potassium bicarbonate in a zinc tube, potas- 

 sium nitrate in a zinc tube, strontium nitrate in a zinc tube, common 

 salt with iodine or bromine in an aluminium tube. 



