4S6 Prof. Andrews on the Thermo-electric Currents 



The extremities of the platina wires which were introduced 

 into the globules of borax, after having been employed in 

 these experiments, did not exhibit any appearance of chemical 

 action ; their lustre was untarnished, and their edges presented 

 a sharp and well-defined outline, without being in the least 

 degree rounded away. To render still more certain the abs- 

 ence of any chemical action, a very fine wire of platina was 

 used as the hottest wire, in contact with the fused borax, and 

 the circuit being completed by a metallic wire, a continuous 

 current was maintained for several hours; but there was no 

 apparent change either in the wires or the borax. With carbo- 

 nate of soda instead of borax, the result was the same. When 

 it is remembered that this current, if transmitted through a 

 solution of the iodide of potassium, (in which case the greater 

 part of the current is even interrupted,) would have produced 

 in a few seconds a very perceptible deposition of iodine, it is 

 impossible to imagine that the same current could continue, 

 for a long space of time, to be produced from chemical action 

 in one of the platina wires without any sensible alteration of 

 the metallic surface. Besides, it is well known that under or- 

 dinary circumstances there is no chemical action exercised by 

 platina upon fused borax or carbonate of soda. 



It is certainly very interesting to see powerful chemical af- 

 finities thus overcome by simply bringing two metalHc wires, 

 at different temperatures, into contact with a fused salt, be- 

 tween which and the wires no [chemical] action takes place. 

 The direction of the current is not influenced by the quantity 

 of surface in contact with the wires, but depends altogether on 

 the difference of temperature, as was ascertained by careful 

 experiments. 



Similar results were obtained when other fused salts were 

 substituted for borax, such as carbonate of potash, chlo- 

 ride and iodide of potassium, sulphate of soda, chloride of 

 strontium, &c. Even with boracic acid, which Faraday has 

 observed to be a very imperfect conductor of voltaic electri- 

 city, I succeeded in deflecting the needle of the galvanometer 

 through an arc of 40°, the circuit being closed by metallic 

 wires. The direction of the current was the same as with 

 borax. 



To compare the intensity of these currents with those pro- 

 duced by chemical action, the galvanometer and a hydro- 

 electric couple were both interposed in the course of the cir- 

 cuit, and the connections were so adjusted, that the currents 

 developed by the fused salt and in the voltaic cell should be 

 in opposition to each other. In this case the deflection of the 

 needle would indicate the current of superior intensity. On 

 comparing these currents with various hydro-electric com- 



