COMBINATION OF OXYGEN AND HYDROGEN BY PLATINA POLES. 59 



minutes ; but if that same plate, instead of being merely rinsed, had been left in 

 distilled water for twelve or fifteen minutes, or more, it would rarely fail, when put 

 into the oxygen and hydrogen, of becoming, in the course of a minute or two, ignited, 

 and would generally explode the gases. Occasionally the time occupied in bringing on 

 the action extended to eight or nine minutes, and sometimes even to forty minutes, 

 and yet ignition and explosion would result. This effect is due to the removal of a 

 portion of acid which otherwise adheres firmly to the plate. 



583. Occasionally the platina plates (569.), after being made the positive pole of 

 the battery, were washed, wiped with filtering-paper or a cloth, and washed and wiped 

 again. Being then introduced into mixed oxygen and hydrogen, they acted appa- 

 rently as if they had been unaffected by the treatment. Sometimes the tubes con- 

 taining the gas were opened in the air for an instant, and the plates put in dry ; but 

 no sensible difference in action was perceived, except that it commenced sooner. 



584. The power of heat in altering the action of the prepared platina plates was 

 also tried (595.). Plates which had been rendered positive in dilute sulphuric acid 

 for four minutes were well washed in water, and heated to redness in the flame of a 

 spirit-lamp : after this they acted very well on mixed oxygen and hydrogen. Others, 

 which had been heated more powerfully by the blowpipe, acted afterwards on the 

 gases, though not so powerfully as the former. Hence it appears that heat does not 

 take away the power acquired by the platina at the positive pole of the pile : the oc- 

 casional diminution of force seemed always referable to other causes than the mere 

 heat. If, for instance, the plate had not been well washed from the acid, or if the 

 flame used was carbonaceous, or was that of an alcohol lamp trimmed with spirit 

 containing a little acid, or having a wick on which salt, or other extraneous matter, 

 had been placed, then the power of the plate was quickly and greatly diminished 

 (634. 636.). 



585. This remarkable property was conferred upon platina when it was made the 

 positive pole in sulphuric acid of specific gravity 1-336, or when it was considerably 

 weaker, or when stronger, even up to the strength of oil of vitriol. Strong and dilute 

 nitric acid, dilute acetic acid, solutions of tartaric, citric, and oxalic acids, were used 

 with equal success. When muriatic acid was used, the plates acquired the power of 

 condensing the oxygen and hydrogen, but in a much inferior degree. 



586. Plates which were made positive in solution of caustic potassa did not show 

 any sensible action upon the mixed oxygen and hydrogen. Other plates made positive 

 in solutions of carbonates of potassa and soda exhibited the action, but only in a 

 feeble degree. 



587. When a neutral solution of sulphate of soda, or of nitre, or of chlorate of 

 potassa, or of phosphate of potassa, or acetate of potassa, or sulphate of copper, was 

 used, the plates, rendered positive in them for four minutes, and then washed in water, 

 acted very readily and powerfully on the mixed oxygen and hydrogen. 



588. It became a very important point, in reference to the cause of this action of 



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