Us€ of Sulphate of Copper, ^c. m Bread. 



271 



No. 



2 

 3 

 4 

 5 

 6 



Quantity of sulpb.' Action of fenocyanate of 

 of coppei- in bread. | potash. 



2 



2 9 



JL 



15 3 



^1 



8 7 



I 



7 3 6 



J__ 



3 S 9 



^I 



18 7 5 



Very apparent rose color, 

 A"deeper rose color. 

 . Blood red. 

 Crimson (deep.) 



Action of hydro-sulphate of 

 aiiiinonia. 



Brownish color. 

 Apparent brown. 



It is obvious that hydro-sulphate of ammonia is much less decisive 

 than the ferrocyanate of potash. Liquid ammonia produces a sen- 

 sible blue color by contact with bread, only when the sulphate of 

 copper is in such quantity as tcf occasion a green color in the bread. 



The author considers the ferrocyanate of potash as a test suffi- 

 ciently delicate to shew the presence of copper in quantities injurious 

 to health. ; but to determine its existence in the smallest quantities, 

 the method which he prefers is to burn in a platina capsule two hun- 

 dred grammes of the bread to be examined, reduce the cinders to 

 fine-powder; mix this with ei^Jit or ten grammes of nitric acid ; 

 heat the mixture till the free acid is evaporated, dilute the pasty mass 

 with distilled water aided by heat, filter, add a small excess of liquid 

 ammonia and a few drops of a solution of sub-carbonate of ammonia. 

 When cold, filter again, heat to ebullition so as to expel the excess 

 of amiTionia, and until the fluid is reduced to a fourth of its volume. 

 This fluid, acidified by a drop of nitric acid,' is divided into two parts ; 

 to one is added hydro-ferrocyanate of potash ; to the other hydro- 

 sulphuric acid or hydro-sulphate of ainmonia. This process, says 

 the- author, if punctually followed, will shew, by the first of these 

 tests, the presence of one part of sulphate of copper in 70,000 of 

 ,bread. by the immediate production of a rose color, and a light crim- 

 son precipitate after a few hours' repose. The hydro-sulphate pro- 

 duces a light fallow color, and a brown precipitate. ' If the copper 

 exist in greater quantity, a polished blade of iron in the solution will 

 indicate its presence. The calcination of the bread in an earthen 

 crucible would require six or eight hours ; in a platina capsule two 

 or three hours are sufficient. 



The precipitate occasioned by the ammonia, consists principally 

 of phosphate of lime, phosphate of magnesia, oxide of iron, and a 

 small quantity of alumine. The first filtration may be dispensed 

 with when the detection of the copper is the sole object= 



