466 



Dr. C. R. A. Wright and Mr. C. Thompson. [Mar. 28, 



and determined. Owing to the solntion of lime, alumina, &c., from 

 the vessels used during evaporation, we found that too high a value 

 was always obtained by directly precipitating zinc with sodium car- 

 bonate from the acid fluid ; wherefore we first precipitated it as sul- 

 phide by means of ammonia and ammonium sulphide, and redissolved 

 the precipitate in dilute hydrochloric acid (after collection on a filter) 

 before precipitating as carbonate. Any traces of zinc not thrown 

 down thus were precipitated by adding a few drops of ammonium 

 sulphide to the filtrate and thus estimated, whilst any traces of 

 alumina and iron contained in the zinc oxide were determined and 

 subtracted (after weighing) by dissolving in hydrochloric acid and 

 supersaturating with ammonia. Usually these various filtrate and 

 other corrections were all but infinitesimal : the analyses generally 

 added up to 99 '8 to 99*9 per cent., and the percentages finally quoted 

 are usually reckoned upon the sum of the tin, lead, and zinc found 

 as 100 ; in some cases, more especially with the lighter alloys, the tin 

 and lead only were determimed, the zinc being taken by difference. 



.Forty compound ingots (20 in each series) thus treated gave 

 numbers concording together reasonably well, furnishing the follow- 

 ing averages; in several cases duplicate ingots were prepared, the 

 mean values being those quoted. 



Series I. Temperature near 565. 



In each series the last mixture yielded so thin a layer of lighter 

 alloy that it was impossible to saw off a sample free from admixture 

 with a large amount of heavier alloy. 



