152 A. L. Day and R. B. Sosman — 



since the impurities were weighed to the tenth of a milligram, 

 the results are generally stated to the ten-thousandth of a per 

 cent. This does not mean that the results are considered accu- 

 rate to this figure. The variation in successive determinations 

 comes in the thousandths, so that the fourth decimal place 

 may have about as much value as the second in an ordinary 

 analysis. Great pains have been taken to purify precipitates, 

 often by many precipitations, so that in all cases the figures given 

 may be regarded as minima. In all cases, too, I have endeav- 

 ored to avoid missing anything, by repeating every process, 

 rejecting no precipitate or solution until it was decided that 

 nothing more was to be gotten from it. In any reasonable 

 case of suspicion, blank determinations were made with the 

 reagents.* 



Heraeus* Palladium. 



The palladium was naturally suspected to contain other 

 metals of the platinum group. It is well known that the sep- 

 aration of these metals is a problem of unusual difficulty. The 

 plan here was therefore to precipitate most of the palladium 

 from solution as one of its characteristic compounds and, 

 while the filtrate was reserved for impurities, to redissolve and 

 again precipitate the metal as another characteristic compound. 

 In this way it was hoped that those impurities which were 

 retained by the first precipitate would not be occluded by the 

 second. The sheet metal was first cut into shavings on a mill- 

 ing machine which was especially cleaned for the purpose. 

 Then the shavings were boiled a short time with dilute hydro- 

 chloric acid to remove any iron from the surface, washed and 

 dried. After an unsuccessful endeavor to dissolve the palla- 

 dium in nitric acid (insoluble brown hydroxide (?) always 

 formed), it was dissolved in aqua regia and rid of nitric acid 

 by successive evaporations with excess of hydrochloric acid. 

 It was then dissolved in dilute hydrochloric acid and diluted 

 further to about 11. Ammonia was added in excess.f A pre- 

 cipitate came down and redissolved on warming — all but a 

 little ferric hydroxide which was filtered off. The filtrate was 

 then evaporated again to about 250 cc , diluted and precipitated 

 with stirring, by dilute hydrochloric acid. The voluminous 

 precipitate of PdCl 2 .2]^II 3 " was now filtered and washed on a 

 Biichner porcelain funnel, using suction. The filtrate we will 

 call ' ; solution A." The precipitate was then dried and 



* After considerable experience in the examination of these " pure " 

 metals, the writer has reached the conclusion that a 10 g. portion, in the 

 great majority of cases, will give as satisfactory results as a larger portion 

 and with far less labor. 



fE. F. Smith and H. F. Keller, Amer. Chem. Jour., xiv, 423, 1892. 



