106 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



799. In one experiment of this kind I used borate of lead (408. 673.). It evolves 

 lead, under the influence of the electric current, at the anode, and oxygen at the cathode-, 

 and as the boracic acid is not either directly (408.) or incidentally decomposed during 

 the operation, I expected a result dependent on the oxide of lead. The borate is not 

 so violent a flux as the oxide, but it requires a higher temperature to make it quite 

 liquid ; and if not very hot, the bubbles of oxygen cling to the positive electrode, and 

 retard the transfer of electricity. The number for lead came out 101*29, which is so 

 near to 103*5 as to show that the action of the current had been definite. 



800. Oxide of bismuth. — I found this substance required too high a temperature, 

 and acted too powerfully as a flux, to allow of any experiment being made on it, 

 without the application of more time and care than I could give at present. 



801. The ordinary protoxide of antimony, which consists of one proportional of 

 metal and one and a half of oxygen, was subjected to the action of the electric current 

 in a green glass tube (789.), surrounded by a jacket of platina foil, and heated in a 

 charcoal fire. The decomposition began and proceeded very well at first, apparently 

 indicating, according to the general law (679. 697.)5 th^t this substance was one 

 containing such elements and in such proportions as made it amenable to the power 

 of the electric current. This effect I have already given reasons for supposing may 

 be due to the presence of a true protoxide, consisting of single proportionals (696. 

 693.). The action soon diminished, and finally ceased, because of the formation of 

 a higher oxide of the metal at the positive electrode. This compound, which was 

 probably the pei'oxide, being infusible and insoluble in the protoxide, formed a cry- 

 stalline crust around the positive electrode ; and thus insulating it, prevented the 

 transmission of the electricity. Whether if it had been fusible and still immiscible 

 it would have decomposed, is doubtful, because of its departure from the required 

 composition (697.)- It was a very natural secondary product at the positive elec- 

 trode (779.). On opening the tube it was found that a little antimony had been 

 separated at the negative electrode ; but the quantity was too small to allow of any 

 quantitative result being obtained. 



802. Iodide of lead. — This substance can be experimented with in tubes heated by 

 a spirit-lamp (789.) ; but I obtained no good results from it, whether I used positive 

 electrodes of platina or plumbago. In two experiments the numbers for the lead 

 came out only 7S'46 and 73*45, instead of 103*5. This I attribute to the formation 

 of a periodide at the positive electrode, which dissolving in the mass of liquid iodide, 

 came in contact with the lead evolved at the negative electrode, and dissolved part of 

 it, becoming itself again protiodide. Such a periodide does exist ; and it is very 

 rarely that the iodide of lead formed by precipitation, and well washed, can be fused 

 without evolving much iodine, from the presence of this percompound ; nor does cry- 

 stallization from its hot aqueous solution free it from this substance. Even when a 

 little of the protiodide and iodine are merely rubbed together in a mortar, a portion 

 of the periodide is formed. And though it is decomposed by being fused and heated 



