+. 
Use of Sulphate of Copper, &e. in Bread. 271 
No.| i of er | Action of ferrocyanate of jAction of hydro-sulphate of | 
" jof copper in bread. potash. i ee 
Se 
I 39005 | : ne song 
S SMbes rt ee 
‘ez sas Very apparent rose Phi 
4) ages eeper rose c os 
3 ee ‘Blood red. ‘| Brownish color. | 
6 tez5 | ~ Crimson (deep.) Apparent brown. |” 
| 
~ jaf 
ti is soliaictl that Sorlatesintaste of ammonia is much tle 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 to 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 eight or ten grammes of nitric acid ; 
heat the mixture till the free acid is evaporated, dilute thé 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’ 
ofa ammonia, and until the fluid is reduced to a fourth of its volume. 
luid, 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 ammonia. ‘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 erim- 
son precipitate after a few hours’ repose. ‘The hydro- solhté 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 pe tw 
or three hours are sufficient. 
recipitate occasioned by the ammonia, “consists princip Vv 
of phosphate of lime, phosphate of magnesia, oxide of iron, and a 
small quantity of alumine. The first filtration may be dispensed 
with wen the detection of the copper is the sole object. 
