Copper was found in some of the foods examined, and since copper 

 sulphid is more soluble in ammonium sulphid than in potassium 

 hydrate, it seemed advisable to use the latter. 



A muffle 9 by 21 inches will hold 10 crucibles at a time, and one 

 analyst can easily make 20 determinations in a week. If the heating 

 in the muffle is gradual and the crucibles are removed as soon as all 

 of the carbon is destroyed, the crucible will not be blistered on the 

 outside and only slightly on the inside, and can be used for repeated 

 fusions. If the crucibles have been spun with a copper or brass tool, 

 the traces of copper adhering to the crucible should be filed off. 

 Fifteen determinations can be weighed, dried, and burned in nine 

 hours, using a hot plate 14 by 18 inches, and a muffle 9 by 21 inches. 

 This requires three hours' continuous watching, and then only an 

 occasional inspection of the muffle and changing the position of the 

 crucibles. Straight ashing, on the other hand, requires at least seven 

 hours' burning in the muffle if even approximately accurate results 

 are to be obtained and if the food can -be put into the muffle without 

 previous drying. 



Two hundred and fifty determinations were made in working out 

 the details of this proposed method. 



[Cir. 67] 



