284 Journal of Agricultural Research voi. xxu.no.s 



As a rule, 25-cc. aliquots were evaporated to dryness in 50-cc. por- 

 celain dishes on the steam bath, and the residue was taken up in 5 cc. 

 of distilled water. Two drops of acetic acid and 3 drops of i per cent 

 solution of potassium ferrocyanid were added, and the color was im- 

 mediately compared with that of standard solutions of copper sulphate 

 which had been evaporated with ammonium nitrate and taken up in 

 5 cc. of distilled water. 



Copper in the ground tubers was determined by the same procedure, 

 using 50 gm. of the moist sample. The analytical data are recorded in 

 Table I. 



DieTERMINATlON OF COPPER IN SOEUS 



One hundred gm. of the well-mixed soil samples were treated with a 

 mixture of 80 cc. of nitric acid and 20 cc. of sulphuric acid in large por- 

 celain casseroles. The mixtures were heated on the steam bath and 

 til en on the hot plate until the nitric acid fumes were removed. The 

 residues were extracted with 200 cc. of water, filtered, washed, and made 

 to 500 cc. volume. After evaporation to 200 cc, the iron was precipi- 

 tated with ammonia and the solutions were made to volume. They were 

 next filtered and aHquots were made acid with hydrochloric acid, through 

 which hydrogen sulphid was passed for 20 minutes, or until all the copper 

 was precipitated. The precipitated copper after settling was filtered 

 and dissolved in 10 cc. of nitric acid, the filter paper and precipitate being 

 transferred together. Ammonia was added to faint alkalinity, and the 

 solutions were evaporated to dryness in small porcelain dishes. The resi- 

 dues were taken up in 5 cc. of distilled water, two drops of acetic acid 

 and three drops of i per cent potassium ferrocyanid were added, and the 

 copper was estimated by colorimetric comparisons. In some cases after 

 evaporation to dryness it was necessary to take up in water, filter, wash, 

 and repeat the evaporation to remove precipitated material. 



If present in large enough amounts copper may be determined electro- 

 lytically, by a method based on the procedure given by Forbes, Free, and 

 Ross.^ 



The results of the analyses of the first and last samples of soil taken 

 appear in Table II. This table gives also the results of a series of tests 

 on the soil around the roots of potato plants which had been commer- 

 cially sprayed with Bordeaux, with Pickering spray, and with a solution 

 of copper sulphate, to determine whether any appreciable amounts of the 

 copper occur in the soil beneath the sprayed vines. 



> Forbes, R. H. certain effects under irrigation of copper compounds xtpon crops. Arlr. Agr. 

 Exp. Sta. Bui. 80, p. 145-238. 16 fig., 4 pi. (i col.). 1916. Bibliography, p. 236-238. Part 3, Appendix: 

 Methods of analysis, with the collaboration of E. E. Free and W. H. Ross, p. 229-233. 



