678 TRANS. ST. LOUIS ACAD. SCIENCE. 



Copper — White. 



Cadmiim — White. 



Zinc White; is very volatile. 



As the copper, cadmium and zinc iodides are white, the tablet 

 should first be coated with a film of soot, by holding- it in a smoky 

 flame, in order to give a black background to show oft" these white 

 coats. 



These three white coats closely resemble one another in their 

 properties, and in order to distinguish them it is necessary to blow 

 on them vapors of ammonium sulphide, when they are converted 

 into their sulphides, and consequently will turn black in the case 

 of copper, yellow with cadmium, and remain white with zinc. 

 The copper iodide also gives the characteristic bluish-green color 

 to the flame as it passes oft', so that it can be readily determined 

 even in the presence of zinc and cadmium. 



If to the peculiar velvety-appearing chocolate-brown coating of 

 bismuth a drop of dilute ammonia be added, or ammonia vapors 

 be blown over it, the brown disappears, leaving a brilliant red 

 coat. 



Many of these coats are more or less evanescent, and disappear 

 on prolonged exposure at ordinary temperature. 



These coats will be found to be very striking and characteris- 

 tic, and are very delicate, when compared with the usual blow- 

 pipe tests. It will be furthermore observed that we are now able 

 to distinguish tin and zinc in the presence of each other, which 

 has hitherto been impossible with the blowpipe alone. 



In the case of complicated mixtures, the above metals cannot 

 be satisfactorily distinguished from one another by this reagent, 

 and it will not answer as a substitute for the old method, that 

 necessitates a separation of them into groups. Bnt for individual 

 cases and confirmatory tests, especially when delicacy is required^ 

 it will be found to be a most valuable acquisition to the blowpipe 

 outfit. 



In the course of some experiments on these iodide reactions it 

 occurred to the writers that they could be as satisfactorily pro- 

 duced by the use of tincture of iodine. On following up this idea 

 with a series of tests it was found that the tincture was quite as 

 satisfactory as the hydriodic acid, while it has the great advantage 



