1/4 Sanitary Studies of Bak'mg Powders 



pleted, the method adopted by the Assoc. of Official Agric. Chem- 

 ists (2), with a slight modification, was chosen. . . . This method 

 was followed precisely with one exception: instead of fusing the 

 combined phosphates (after ignition) with sodium carbonate, the 

 iron was determined by the Zimmerman-Rheinhardt method (3) in 

 an ahquot portion of the original acid sol. The calculated amount 

 of FeP04 was subtracted from the combined weights of AIPO4 ^i^d 

 FeP04. Many determinations were made by this method on mix- 

 tures of pure Solutions of ferric chlor id and almn, and perfectly 

 accurate results were ohtained." 



Later Dr. Max Kalin (4), while working on a similar problem, 

 re-verified the accuracy of the method chosen by Steel (5). 



The principal objection to the method is the length of time re- 

 quired to perform it. This factor has led other analysts to seek a 

 shorter but equally accurate method. In 1912, Schmidt and Hoag- 

 land (6) published a method which they claimed to be comparatively 

 quick and accurate. 



II. Experimental work. i. Reagents and apparatus em- 

 PLOYED. The reagents used in this work were selected with the 

 greatest care and tests were made to verify their purity. The potas- 

 sium permanganate sol. used was an old sample of good quality. 

 The sodium Oxalate used in standardizing the potassium permanga- 

 nate sol. was a " Bureau-of-Standards Standard sample No. 40." All 

 the pipettes, burettes, and Volumetrie flasks used were standardized 

 before using. 



The following reagents were made up before starting the analytical 

 experiments : 



A. — Potassium permanganate Solution: w/40, 



B. — Stannous chlorid: 50 gm. of the pure crystallized salt were 

 dissolved in 100 cc. of hot conc. hydrochloric acid and 

 made up to i 1. with dist. water. 



C. — Mercuric chlorid: A cold saturated Solution. 



D. — Preventive sol.: (a) 100 gm. of manganese sulfate were 

 dissolved in 500 cc. of water; (b) 200 cc. of H2SO4 were 

 poured into 300 cc. of water and 500 cc. of syrupy phos- 

 phoric acid (1.3 sp. gr.) added; then (a) and (b) were 

 mixed. 



