859 

 soMK .\o'i'|.;s (IN 'I'liK i;s'ri.MA'ri(».\ ok niitoMii m as ("iiifoMir 



\Vm. M. I'.i.a.nc iiaki) and Paulink Xokkis. 



Sclilnn (riiciu./tf;.. .{.{. S77) st.itcs tliiit clironiiuin can ho (lcformino<l 

 frraviinctriojill.v by itr('('ii)itatinii fidin ;i chrdiiiic salt by aimiioiiinin iiifritc 

 solution ami ifjnitiiif,' the iin>cii>itat(' with llu' tiitor in a Rose crnciblc. 



Scboi'Uor and Schrautli ( Clicni.-ZtK.. .«, VSM ) state that acc-uratc f,'ravi- 

 nu'tric dt'torniinations of clu-oniiuui may bo made by procipitation from a 

 iioilhifr. dilute solution of tlio ciiiomic salt by the addition of one oo. of 

 aniliife and boiling for five minutes. The jirecipitate is filtered, washed, and 

 ijiuitod. 



Hanus and Lukas (Nth. Intern. ('onj;r. Appl. ("hem.. I. 1J()!I-12) state that 

 chromic hydroxide can be precipitated (piantitatively from neutral or alka- 

 line solutions oontainiuj; chromates by hydrazine hydrate and some of its 

 derivatives. 



KothauK (Z. anorj;-. ("hem., s',. KIH-Sin states that a long series of estima- 

 tions made by precipitating chromium hydroxide by means of ammonium 

 hydroxide, ammonium sulphide, the iodide-iodate method, and by hydroxyl- 

 amino. gave results running high from O.lT^r to 1.60%. the error being due 

 to the formation of chromic chromate during the ignition. 



These statements are interesting compared with the assertions of Fres- 

 eiiius (Quant. Chem. Analysis. 6th. Ger. Edition. Cohn's Eng. Translation, 

 p.igc I'Sl ) that when chromium is precipitated in glass vessels, the results 

 are high owing to contamination with silica; if the precipitation is carried 

 out in porcelain vessels, the results are much more satisfactory, and if 

 Iilatinimi vessels are used, the results are quite acciu'atv. 



With a view to verifying the statements of Fresenius or those of Roth- 

 aug. the following exiieriments were made: The purest obtainable potas- 

 sium dichromate was carefully recrystallized and the chromium estimated 

 by evaporating to dryness solutions to which were added ethyl alcohol and 

 hydrochloric acid, redissolving, and precipitating the chromium from boiling 

 dilute solutions with ammonium hydroxide. After washing, the precipitate 

 was ignited with the filter, heated over a Meeker burner and afterwards 

 with blast lamp, cooled and weighed. ().ir)(K) gram of the dichromate was 

 taken each time: this «piantity should give O.dTT.") gram chromic oxide. 



Five determinations in lioakors of tlio best American glass gave 

 (>.(»701. 0.0797. 0.0791. 0.0794. 0.079"). 



Five determinations with precipitation in a largo pon-olain cass(>rolo gave 



(».()7;>4. 0.0790. o.inm. o.oim. 0.0794. 



Five determinations with precipitation in a largo ]ilatinum dish gave 

 0.079S. 0.0797. 0.0791. 0.(>792. 0.0794. 



Three determinations with glass beakers, the ]>rociiiitato lioing dissolved 

 and reprecipitate. ga\e 0.079(i. 0.0790, 0.07.S9. 



