474 Some Properties of Dried Hydrogen Sulphide Gas. 



difference of weight as an indication of chemical change, the 

 differences of colour produced by the formation of the sulphides 

 of various metals, by the action of hydrogen sulphide on com- 

 pounds of these metals, were taken. The method of experiment 

 was its follows : — A short strip of ordinary filter-paper was 

 taken and moistened with lead acetate, then dried in a water- 

 bath and placed in a straight glass tube, wmich took the place 

 of the experimental U-tube in the previously described experi- 

 ments, and accordingly was connected up with the drying 

 apparatus. Through this hydrogen was passed as before, 

 then the hydrogen-sulphide gas for about two hours. The 

 paper remained perfectly white and unaltered in the dry gas. 



If, however, the paper was purposely only partially dried, 

 or if a little liquid water was placed in contact with the dried 

 paper, then the H 2 S gas instantly turned the paper black *. 

 If two tubes, one containing the dried-lead -paper and the 

 other a partially dried lead-paper, be placed side by side, and 

 if the dried gas be passed first through the one tube and then 

 through the other, the difference between the action of the 

 gas on the paper in the two is very striking — the dried one 

 remaining quite white throughout, whilst the other is instantly 

 blackened by the gas. 



A similar comparative experiment was performed in the 

 case of paper moistened with a solution of arsenic tri-chloride : 

 the dried paper remained quite unaltered, whilst the other was 

 instantly turned yellow. With salts of tin, cadmium, bismuth, 

 antimony, silver, copper, mercury, and cobalt, similar experi- 

 ments were conducted, the results being in all cases exactly the 

 same ; in the case of antimony, cadmium, and tin the differences 

 are very striking. In all these cases, then, it was shown, by a 

 comparative experiment of the kind described, that dried 

 hydrogen sulphide has no action on the dried soluble salts of 

 the metals before mentioned, whereas, if moisture be present 

 and in contact with the substance investigated, the change at 

 once takes place. 



Further, it was observed that the dried gas has no action 

 whatever on dry blue litmus-paper, whereas moist litmus-paper 

 is instantly reddened. 



The conclusion arrived at from these experiments is that 

 dried hydrogen sulphide has no action on magnesia, baryta, 

 sesqui oxide of iron, or on salts of silver, copper, mercury, lead, 

 bismuth, cadmium, arsenic, antimony, tin, and cobalt ; nor 

 has it the power of reddening blue litmus-paper, whereas in 



* If, however, the lead-paper previously dried be moistened with 

 absolute alcohol, instead of water, the darkening produced by hydrogen 

 sulphide is very slight, although the gas is more soluble in alcohol than 

 in water. 



