SPECIAL TESTS 



17 



mine give the copper ferrocyanide reaction when placed in an acidulated solution of 

 potassium ferrocyanide. 



The following table from the work by Koenig gives the relative 

 sensitiveness of the tests above described:^ 



Elements in 



combination 



valency 



Reaction 



Bo'". 



As'", 



Sb'". 



Sn". 



Au'" 



Pt"" 



Cu". 



Ag'.. 



Hg'. 



Hg". 



Pb".. 



Bi"'. 



Cd". 



Fe". 



Co"., 



Ni"., 



Curcuma thread 



Sulphide thread 



Sulphide thread 



Violet color with sulphide thread 

 Sulphide thread — brown, purple . . 



Sulphide thread 



Sulphide thread + ferrocyanides. 



Sulphide thread + Ag 



NH3 vapor 



Sulphide thread 



Sulphide + PbCrO, 



Sulphide + chromate + Bi 



(NHsSH) vapor 



(NH3SH) — blue 



NH3SH or nitroso — beta — naph- 



thol 



NH3SH 



Limit 

 (mg. X io») 



1 ,0 

 30 

 3-0 

 8,0 



50 

 8.0 



5° 

 8,0 

 8.0 

 6,0 

 8.0 



0-3 

 0-3 



Comparative 

 sensitiveness 



I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 

 I in 



33,000 



2,500 



40,000 



20,000 



2 2,000 



6,000 



4,000 



22,000 



25,000 



20,000 



13,000 



9,000 



9,000 



3,5°° 



I in 100,000 

 I in 100,000 



9. Making Analytical Reports 



The methods of micro-analysts, whether in private, commercial 

 or government laboratories, should be uniform. Much could be 



'■ The comparative degree of sensitiveness of the different chemical compounds 

 concerned in the color reactions above described and tabulated is indicated by the 

 number of cubic centimeters in which i gram of the substance in solution is 

 still appreciable. The actual limit, determined experimentally, is indicated in 

 terms of milligrams, that is o.ooi mg., represented by ^g- Expressing the com- 

 parative sensitiveness (CS) in a formula we have 



Mg hmit ^ , molecular weights 



CS = 



X 



amount limit ^ combination valency 

 or to give the example for boron, we have 



CS = 



300I 59 



7 X'T = 33.000- 



0.00000000 3 



