MTCROCHEMICAL REACTIONS OF SILVER 
379 
such conditions it is necessary to exercise the greatest care in 
order to avoid missing the little silver which is present. 
Elements forming oxychlorides may under exceptional con¬ 
ditions be precipitated with the silver. 
It is also well to bear in mind that the addition of hydrochloric 
acid may force back the dissociation of certain salts to a degree 
causing the separation of a solid phase. 
Precautions. 
When working with concentrated hydrochloric acid or strong 
ammonia, great care must be used to avoid spoiling the micro¬ 
scope and objectives. It is essential to work rapidly. 
The drop is acidified with nitric acid because the presence of 
this reagent favors the agglutination of the particles of silver 
chloride, and hinders at the same time the precipitation of oxy¬ 
chlorides, etc. 
Decanting after precipitation is advisable, since the crystal 
form of silver chloride is changed by many compounds when the 
former is crystallized in the presence of the latter. Still other 
compounds completely ruin the test. Although there is, of 
course, danger of the occlusion of some of these objectionable 
salts by the silver chloride, this difficulty is reduced to a mini¬ 
mum by avoiding too concentrated test drops and washing the 
precipitate. 
Washing the precipitated silver chloride with hot water re¬ 
moves the greater part of the lead chloride which may have been 
carried down with the silver. 
EXPERIMENTS. 
a. Precipitate with dilute HCl, a test drop containing AgNOs. Separate and 
wash the precipitate; then recrystallize it by the above described method, using 
concentrated HCl. Then repeat the experiment, using NH4OH as the solvent. 
b. Make a mixture of Ag and Pb, test by both recrystallization methods. 
c. In like manner test a mixture of AgNOs and HgNOs. 
d. Precipitate with HCl a test drop containing Pb and Ag; recrystallize the 
precipitate without drawing off the solution. In like manner test mixtures of Ag 
and Zn, Ag and Cd, Ag and Sb, Ag and Pt, Ag and Sn, Ag and Cu. 
e. Try recrystallization of AgCl in the presence of phosphates, in the presence 
of sulphates and in the presence of molybdates. 
