208 Dr. Gibbs’s Contributions to Analytical Chemistry. 
L, BY: means of Crum’s test it is easy to detect the presence of 
the ;s;'s¢— of manganese in asolution otherwise colorless. With 
proper care a much smaller quantity of the metal may be detect- 
ed, but the above will form a good practical limit to the sensibil- 
ity of the reaction. ‘ 
. The manganese in this reaction may be present as chlorid, 
nitrate, oe or phosphate, without effecting the result. 
a * resence of sulphate or nitrate of ammonium even in 
very a excess does not sensibly affect the delicacy of the re- 
action. 
The presence of chlorid of ammonium in sinall quantity 
does not affect the reaction. When, however, the chlorid is 
present ‘in great excess, it is necessary to add a very large propor- 
tion of peroxyd of lead in order to obtain the characteristic rose 
or violet tint, as the lead is reduced to a chlorid so long as there 
is sal-ammoniac i in the solution. In this case, therefore, “it is better 
to precipitate the suspected liquid by sulphydrate of ammonium, 
and then to test the precipitate by nitric acid and peroxyd of lead. 
hen organic substances are present, the solution should 
either be evaporated to dryness and ignited, or else precipitated by 
sulphydrate of ammonium, and the precipitate tested. e first 
method would probably answer best in testing mineral waters. 
. The bases to be tested for manganese may be present as mil- 
trates, sulphates, or chlorids. In the latter case the characteris- 
tic violet or rose color makes its appearance, even though chlorine 
is Corts evolved from the solution, on boiling with the nitric 
acid and peroxyd of lead. 
The presence of iron even in large excess does not very 
sensibly affect the delicacy of the reaction 
. The presence of an excess of a salt of nickel completely 
prevents the reaction for manganese, the violet color of t 
Hy Darna gnne acid being lost in the green of the nickel com- 
9. The presence of asmall excess of a salt of cobalt does not 
materially affect the reaction for manganese. It is, however, 1™ 
possible by the direct application of Crum’s nt to detect t 
presence of a small quantity of manganese in a large quantity | of 
a 4 compound. 
The difficulty which arises in the application of Cr um’s 
a ia cobalt or nickel is present, may be completely avoided 
Maumené that the colors of solutions of. cobalt and nickel are 
complementary to each other. The solution of cobalt which is 
suspected to contain manganese, is first to be freed as completely 
as possible from arene Sopp. and iron. Toa portion pet ee 
nee is to be gradually added ‘anil the color of the mixed fluid 
™ 
