Dr. Gibbs’s Contributions to Analytical Chemistry. 209 
of lead are then to be added, and the whole boiled for a few 
seconds, when the characteristic tint will appear if but a trace of 
manganese be present. The same process is to be applied in 
of the liquid must be observed immediately after boiling and 
subsidence of the excess of peroxyd of lead, as the tint fades when 
the solution is exposed to air and light. 
The constitution of the black substance which is precipitated 
from solutions of manganese by peroxyd of lead has not yet been 
satisfactorily determined, in consequence of the difficulty of ob- 
taining it perfectly free from an excess of peroxyd of lead, and I 
propose to resume the subject in another paper. It appears, as 
stated by Schénbein, to be a chemical combination of the peroxyds 
of lead and. manganese ; its chemical relations are as follows :— 
ut on heating evolves oxygen, while sulphate of lead is found. 
Oxalic and tartaric acids are readily oxydized by digestion with 
the black compound, with evolution of carbonic acid, and forma- 
Hon of carbonates of lead and manga 
In another memoir I shall return to 
sults of quantitative analyses, conducted acco 
pointed ont in the present communication. It may be proper to 
IS. v k: the commercial peroxyd 
cir eek Deo wn <i Maas or id upon miuium, can 
Law Te 
