150 Dr. Andrews on the Properties of Voltaic Circles. 



gas, mixed with the vapours of sulphur, are disengaged. On examination, this 

 gas was found to consist of a mixture of sulphurous acid and hydrogen gas. 

 When an excess of zinc was employed the hydrogen in the beginning of the pro- 

 cess amounted to 20 per cent, of the whole, but towards the end it increased to 

 nearly 40 per cent. 



A similar portion of zinc being connected with a platina wire, and the free 

 extremities of each being introduced into the same acid, so as to form a voltaic 

 circle, the fine bubbles before described now appeared chiefly on the surface of 

 the platina. When removed they did not form again, unless a fresh surface of 

 zinc was exposed. The gas thus obtained was found to be pure hydrogen. 

 The acid was then heated, but there was no extrication of gas from the sur- 

 face of either metal till the temperature reached 150° cent., and then only a few 

 minute streams arose from the platina wire. At 190° the evolution of gas from 

 the platina wire did not exceed that from the unconnected zinc at 140° or 150°. 

 From 210° to 240° there was rapid effervescence. During the course of the 

 experiment no gas appeared at the surface of the zinc, unless the temperature 

 was very high, so that torrents of gas were disengaged from the platina, when by 

 a close inspection some very fine streams might be perceived forcing a passage 

 from certain points of the zinc surface. The gas extricated from the surface of 

 the platina differed from that obtained when the zinc alone was dissolved, — in 

 the small quantity of hydrogen which it contained, and in that quantity diminish- 

 ing instead of increasing as the solution proceeded. In fact the hydrogen was 

 found to amount to 9 per cent, in the commencement of the experiment, and 

 towards the end it diminished to only 1 per cent., the rest of the gas being sul- 

 phurous acid. A quantity of sulphur was also separated, both when the zinc was 

 alone and connected with the platina, which sometimes appeared in crystals in 

 the acid, at other times became diffused through the mass of the liquid, so as to 

 render it nearly opake, while at high temperatures it was disengaged in the 

 state of vapour. 



Gold and palladium act in the same manner as platina. 



There was no apparent difference in these results, whether pure zinc, or the 

 sheet zinc of commerce was used, and from the uniform surface which it exposes, 

 the latter was employed in all the following experiments. 



To ascertain with precision the retarding influence of the platina upon the 



