170 Proceedings of Indiana Academy of Science 



for ammonia, jDotassium chloroplatinate (2g. per L.) and cobaltous 

 chloride hexahydrate (12g'. per L) ; for nitrites, cobaltous chloride hexa- 

 hydrate (24g. per L.) and cupric chloride dihydrate (12g. per L.) ; and 

 for iron, cobaltous chloride hexahydrate (24g. per L. ) and potassium 

 chloroplatinate (12g. per L.). In the preparation of each solution the 

 salt was dissolved in water, 100ml. of concentrated hydrochloric acid 

 added, and the whole diluted to one liter. 



Kendall and Richards" discussed the factors preventing a perfect 

 match between permanent color standards and the colors obtained with 

 many samples of water. As standards for routine work they do recom- 

 mend the use of a neutral solution of potassium chromate in connection 

 with the Grandval and Lajoux test for nitrates, and of various dilutions 

 of Tidy's formula (0.25g. potassium dichrcmate and d.OLg. cobaltous 

 sulfate heptahydrate per L.) for the determination of ammonia. 



Washburn' ', by combining "in the proper proportions" solutions of 

 ferric chloride, cobaltous nitrate and cupric sulfate, prepared permanent 

 color standards for use in determining the proper iodometric end point 

 in the determination of arsenious acid. 



McBain", in his study on the u.^e of phenolphthalein as an indicator, 

 employed as permanent standards solutions containing mixtures of copper 

 and cobalt salts, acidified with nitric acid to prevent hydrolysis. The 

 most dilute solution contained 0.50g. cobalt nitrate hexahydrate and 0.62g. 

 cupric sulfate pentahydrate per liter; the others contained 2, 3, etc., 

 times these amounts. The difference between any two standards was 

 planned to be equivalent to the color change caused by the addition of 

 one drop of N/250 acid or base. 



Arny' , following Washburn's suggestion for blending solutions col- 

 ored by the cobaltous, ferric and cupric ion, pioposed the adoption of 

 solutions containing these ions as 'international standards for colored 

 fluids". By mixing these three primary colors, red, yellow and blue, in 

 the proper proportions he obtained 88 blends, ranging from the red 

 through to the blue. These solutions are designated a.'^ the "Co-Fe-Cu" 

 standards. In the preparation of the standards, 0.5 N solutions were 

 made of cobaltous chloride, ferric chloride and cupric sulfate by dis- 

 solving the salts in 1 per cent hydrochloric acid. All of the work was 

 checked by means of a Lovibond tintometer, and the acidified solutions 

 Vv-ere found to give the same readings after standing for a year. 



Arny and Pickhardf' discussed the requiiements of satisfactory 

 color standards and reported further observations on the "Co-Fe-Cu" 

 series proposed earlier. This series lacks deep reds and deep blues. 



Arny and Ring' , in the effort to provide for the deficiencies of the 

 "Co-Fe-Cu" .series, proposed a new series of 0.1 N ammoniacal solutions 

 of chloropentammine cobaltic chloride (red), ammonium chromate (yel- 



>-'Tcch. Quar. 17, 277 (1904). 



".Jr. Am. Chem. Soc. .10, :!1 (1908). 



''.Jr. Chem. Soc. li)l. 814 (1912). 



'■• neport 8th Inlr. Comxi: Appl. Chem. 2il, :!19 (1912). 



Jr. Am. I harm. Assoc. 2, 76 (191:5). 

 >" DruKsrisfs Circular r,s, 131 (1914). 

 ■'.Jr. Franklin Ins^t. JSO, 199 (191.')). 



