244 Gooch and Bosworth — Silver as the Chr ornate. 



In Table III are given the results of quantitative experi- 

 ments in which precipitation was effected in presence of nitric 

 acid, with care to insure the necessary excess of potassium 

 chromate. In the experiments of A the precipitate was fil- 

 tered off at once, without solution by ammonia and reprecipita- 

 tion by boiling : in those of B the ammonia treatment was 

 made to convert the less crystalline precipitate to better form 

 for filtration and washing. 









Table III. 









Silver taken K 2 Cr0 4 











as AgN0 3 used 











Volume 



Volume 





HN0 3 







Error 



of solu- 



of solu- 





r * s 



Ag 2 Cr0 4 



Silver 



in terms 



tion 



Weight tion Weight 



Vol. Weight 



weighed 



found 



of silver 



cm. 



grm. cm. 



grm. 



cm 3 . grm. 



A 

 KiCrOi in prese 



grm. 



grm. 



grm. 





Precipitat 



ion by 



nee of HN0 3 . 





25 



0-1355 50 



0-9 



10 0-182 



0-2091 



0-1360 



+ 0-0005 



25 



0-1355 50 



0-9 



10 0-182 



0-2081 



0-1353 



— 0-0002 



25 



0*1358 50 



0'9 



10 0-182 



02090 



0-1360 



+ 0-0005 



25 



0-1355 50 



0-9 



10 0-182 



0-2075 



0-1349 



— 0-0006 



25 



0-1355 50 



0-9 



10 0-182 



0-2090 



0-1360 



+ 0-0005 



Precipitation by K 2 CrOi in presence of HNO3, treatment with NHiOH, and boil- 

 ing to a volume of 10-15 cm3 . 



25 



0-1348 



50 



0-6 



10 



0-063 



0-2076 



0-1350 



-fO-0002 



25 



0-1348 



50 



0-6 



10 



0-063 



0-2068 



0-1344 



— 0-0004 



25 



01348 



50 



0-6 



10 



0-063 



0-2072 



01347 



—o-oooi 



25 



0-1348 



50 



0-6 



10 



0-063 



0-2074 



0-1348 



0-0000 



25 



0-1348 



50 



0-6 



10 



0-063 



0-2070 



0-1346 



-0-0002 



So it appears that from solutions of silver nitrate, containing 

 free nitric acid, potassium chromate precipitates silver chromate 

 completely, provided enough potassium chromate is present to 

 take up the nitric acid with formation of potassium dichromate 

 as well as to form the silver salt. The precipitate, filtered at 

 once or brought to better crystalline condition by treatment 

 with ammonia and boiling of the solution to small volume, 

 may be transferred to the asbestos filter by dilute potassium 

 chromate and washed by small portions of water without 

 appreciable loss. The weight of the residue of silver chromate, 

 dried at gentle heat, may be taken as a very fair measure of 

 the silver originally present. 



