DETERMINATION OF HEAVY METALS. 1411 



In case the filtered extract by any of these methods is colored red or 

 deep yellow, it should be evaporated nearly to dryness, slightly acidi- 

 fied with hydrochloric acid, and boiled a few minutes after the addition 

 of a thread of fat-free wool. If the wool is dyed, it may be examined 

 as directed under coloring matter in Bulletin 65. If the wool is not 

 dyed, the solution is examined spectroscopically. 



If too dilute it may often be concentrated by precipitating the color- 

 ing matter as a lake, a allowing it to settle, decanting off the water, dis- 

 solving in hydrochloric acid, and making alkaline with ammonia. 



In extracting with 50 per cent alcohol the proteids of the meat are 

 coagulated with the formation of a pale, almost white, color. If the 

 meat is not discolored during this extraction, it is probable that some 

 foreign color is present. b 



Marpmann b examines sausages miscroscopically for the presence of 

 coloring matter after dehydrating with alcohol and zylol consecutively, 

 removing the zylol with carbon tetra chlorid and immersing in cedar 

 oil until the natural color of the meat has disappeared. 



DETERMINATION OF HEAVY METALS. c 



Allen's d method for the qualitative detection of tin, copper, lead, 

 and zinc and adapted to their quantitative determination by Bigelow 

 and Munson, 6 was used in this work. Twenty-five grams of the dried, 

 fat-free meat are thoroughly mixed in a porcelain dish with from 

 4 to 5 cc of sulphuric acid, heated upon the water bath, and 2 cc 

 of nitric acid gradually added, with constant stirring until red fumes 

 cease to be evolved; 3 grams of finely powdered magnesia are then 

 added and the mixture ignited in a muffle furnace at low redness. To 

 insure complete combustion the ash may be moistened with nitric acid 

 and reheated. The ash is then taken up with water and several cubic 

 centimeters of hydrochloric acid, evaporated to expel a greater part of 

 the acid, and then transferred, without filtering, to a beaker. The 

 solution should now measure about 100 cc. The solution is saturated 

 with hydrogen sulphid and then heated upon the water bath for several 

 minutes until the precipitated sulphids collect and settle to the bottom. 

 The sulphids and insoluble residue, which may contain some tin oxid, 

 are filtered, the filter ignited, and the mass fused in a porcelain crucible 

 with 3 grams of a mixture of equal parts of potassium carbonate, 

 sodium carbonate, and sulphur. The fused mass is then taken up with 

 water and filtered. Lead and copper, if present, will remain as sul- 

 phids upon the filter. The filtrate is acidified with acetic acid when the 

 tin sulphid is precipitated. This may be collected, washed, ignited, 



a Bremer, Forschungsber. , 1897, 4, 45. 



b Marpmann, -Ztschr. ang. Mikr., 1895, 1, 12. 



e The determinations of heavy metals for the bulletin were made by Mr. Munson. 



d Com. Org. Anal. 2d ed., vol. 4, p. 299. 



e Jour. Am. Chem. Soc., Proc., 1900, 22, 32. 



