60 PEOCEEDINGS OF THE AMERICAN ACADEMY 



the melting point of silver ; but, as soon as our suspicions were aroused, 

 we detected a slight mirror near the open end of the reduction tube, 

 which, when dissolved off with a few drops of nitric acid, and tested 

 with hydrochloric acid, gave abundant evidence of what had taken 

 place. And, by subsequent experiments in a stream of hydrogen gas, 

 we found that, under the conditions present in our experiments, silver 

 volatilized — very slightly, it is true, but markedlj^ — at a temperature 

 considerably below its melting point. 



We have thus shown, first, that recently reduced silver exerts a 

 catalytic action precisely similar to that of spongy platinum, although 

 not so powerful ; and, secondly, that under these conditions the silver 

 slowly volatilizes, at a temperature considerably below its melting 

 point. Whether the volatilization is increased by the catalytic 

 action, or why, in our experiments, the loss should have been so 

 constant in amount, we have had no opportunity to determine. It 

 was only necessary at the time to establish the feet that the results 

 were vitiated by this constant error, and we at once hastened to deter- 

 mine whether the sulphide could be perfectly reduced at a temperature 

 below that at which silver volatilizes in a current of pure hydrogen. To 

 this end, we made many experiments, carefully testing in each case the 

 reduced silver for sulphur, and examining with the greatest care the 

 interior surface of the porcelain tube for any evidence of volatilization. 

 We thus found that, by regulating the temperature, sulphide of silver 

 could be perfectly reduced at a low red heat, without giving any evi- 

 dence of loss from this cause. The following determinations were 

 made in this way : — 



Reduction of Argentic Sulphide. 



Second Series of Expeeiments at Low Red Heat. 



■Kr„ Wt. ofAgjS, Wt. ofS At. Wt. ofS. At. Wt. of S. 



•""• grammes. by loss. Ag = 108. Ag = 107.93. 



l,a. 7.5411 0.9773 32.160 32.139 



2, a. 5.0364 0.6524 32.143 32.122 



3, i. 2.5815 0.3345 32.155 32.134 

 4,c. 2.6130 0.3387 32.168 32.147 

 5,d. 2.5724 0.3334 32.164 32.143 



Mean value 32.158 32.137 



Extreme variation from mean . 0.015 0.015 



