i66 Sanitary Studies of Baking Powders 



ignited to ALOg over a blast and weighed as such. After digestion 

 with HCl and water, the precipitate gave only a very faint test for 

 Sulfate, showing that the decomposition to AI2O3 was complete. 



II. In Det'ns 4, 5, 6, 7, 8, and 9 (Table i), the aluminum in 

 each case was precipitated by NH4OH as AI (OH) 3 in the presence 

 of NH4CI, ignited and weighed as AI2O3. In Det'ns 4, 5, 6, 7, the 

 ignitions were made in porcelain; in 8 and 9, platinum was used. 

 The precipitates in Det'ns 5, 6, and 9, were not washed completely 

 free of chlorides, as were the others, but no noticeable Variation 

 occurred on this account. 



SOL. FOR THE TITRATION OF IRON BY THE MODIFIED ZlMMERMAN- 

 Rheinhardt METHOD.^ 



^.— KMnO^: w/50. 



B. — HCl : I part of water to i part of HCl (sp. gr., 1.2). 



C. — SnCla : 450 gm. of the salt in 450 gm. of HCl (sp. gr., 1.2), 



and diluted to 2 1. 

 D. — HgClg : saturated Solution. 

 E. — Preventative sol. : 160 gm. of MnS04-4H20 dissolved in 



1,750 cc. of water, plus 330 cc. of H3PO4 (sp. gr., 1.7) 



and 320 cc. of H2SO4 (sp. gr., 1.84). 



The Zimmerman-Rheinhardt method is conducted as follows : Heat 

 the HCl sol. of iron (which should not be greater than 50 cc. in vol.) 

 to boiling. While hot add SnCl,, drop by drop, tili colorless, then one 

 drop in excess. Add 10 cc. of HgClg sol., dilute to 500 cc. and add 

 6-8 cc. of preventative sol. Titrate with KMnO^ to first appearance 

 of pink that lasts for 20 seconds. 



KMnO^ sol. {n/50). This sol., used in the above method, was 

 standardized as follows. 



(a) Against Standard iron wire by sol. in HCl (i-i), reduction 

 and titration by the above method. {h) Against Mohr salt (Kahl- 

 baum) by sol. in water and titration in the presence of H2SO4. (c) 

 Against Na2Co04 (Bureau-of -Standards Sample No. 40), titrated hot 

 in the presence of H2SO4 to first lasting appearance of pink. 



Concordant results were obtained by these methods. Since the 

 work described in this paper covered a period of several months, the 

 1 Mixer and DuBois : Jour. Amer. Chem. Soc, 1895, xvii, p. 405. 



