33G 
DR. THOMSON ON MANGANESE. 
PROGRESS OF SCIENCE, 
AS APPLICABLE TO THE ARTS AND MANUFACTURES; TO COMMERCE. 
AND TO AGRICULTURE. 
METHOD OF DETERMINING I’HE 
VALUE OF BLACK OXIDE OF MAN- 
GANESE FOR MANUFACTURING, 
PURPOSES. By Thomas Thomson, 
M.D., F.R.S., L. AND E. Regius Pro- 
fessor of Chemistry in the University of 
Glasgow. 
The manganese to ‘be tested must be re- 
duced to a fine powder or brought into the 
state in which it is used by the manufactur- 
ers of bleaching-powder. To determine its 
value, proceed in the following manner : 
Into a balance Florenced flask put 600 
grains of water, and 75 grains of crystals of 
oxalic acid. Then add 50 grains of the man- 
ganese to be tested ; and, as quickly as pos- 
sible, pour into the flask from 150 to 200 
grains of concentrated sulphuric acid. This 
is best done by having a given weight of sul- 
phuric acid, say 210 grains previously weigh- 
ed out in a glass measure, counterpoised on 
one of the scales of a balance. You pour 
into the flask as much of the sulphuric acid 
as you can conveniently. Then, putting the 
measure again into the scale, you determine 
exactly how much has been put in. 
A lively effervescence takes place, and 
carbonic acid gas is disengaged in abundance. 
Cover the mouth of the flask with paper, 
and leave it for 24 hours ; then weigh it 
again. The loss of weight which the flask has 
sustained isexactly equal to the quantity of 
hinoxide of manganese in the powder exami- 
ned. Thus, let the loss of weight be 34 
grains ; the quantity of binoxide of manga- 
nese in the 50 grains of the powder which was 
tested will be 34 grains ; or it will contain 
68 per cent, of pure binoxide of manganese, 
and 32 per cent, of impurity. 
To understand what takes place, it is ne- 
cessary to recollect that oxalic acid is com- 
posed of 2 atoms carbon 1*5;3 atoms oxy- 
gen 3 ; total 4‘5; and that binoxide of man- 
ganese is composed of 1 atom manganese 3'5; 
2 atoms oxygen 2 ; total 5'5. 
The oxalic acid acts on the binoxide by 
abstracting one-half of its oxygen, which 
converts it into carbonic acid ; hence the 
effervescence. 55 grains of pure binoxide of 
manganese would give out 10 grains of oxy- 
gen, which would convert 45 grains of oxa- 
lic acid into 55 grains of carbonic acid 
which escaping, indicate, by the loss of 
weight, the quantity of carbonic acid formed. 
Nows it happen, that the weight of thecarbo- 
nic acid formed isexactly equal to the quanti- 
ty of binoxide of manganese which gives out 
its oxygen to the oxalic acid. Hence, the 
reason of the accuracy of the test. 
In other words, an integral particle of bin- 
oxide of manganese, which weighs 5'5, gives 
out 1 atom of oxygen. This atom of oxygen 
combines with an integrant particle of oxalic 
acid, weighing 4;5, and converts it into two 
integrant particles of carbonic acid, which 
both together weigh 5.5. As this carbonic 
acid escapes, the loss of weight must be just 
equal to the quantity of binoxide of manga- 
nese in the powder subjected to experiment. 
In practice, I find that a small quantity of 
the binoxide of manganese sometimes escapes 
the action of the oxalic acid, being probably 
screened by the great quantity of impurity 
with which it is mixed. But the deficiency 
of carbonic acid occasioned by this is about 
made up by the moisture which the carbonic 
acid gas carries off along with it. 1 his ren- 
ders the error in general trifling. 
It will be proper to subjoin an example or 
two of the method of proceeding, to enable 
the reader to judge of the goodness of this 
test, and its value to the manufacturer. 
The black oxide of manganese employed 
was subjected to analysis, and found com- 
posed of Binoxide of manganese 68.49 Pero- 
xide of iron 11.85 ; Water 5.6;8 earthy mat- 
ter 13.98 ; total. 100.00 
Experiment 1. 
Put into the flask — Water 599 grs. 
Oxalic acid . , 75, 
Black oxide . . 50, 
Sulphuric acid 1 84 , 
Total . . 908 
Loss of weight 32'5 grains. It ought to 
have been 34-245 grains. Eri’or 1'745 grains. 
; Experiment 2. 
Put into the flask — Water 600 grs. 
Oxalid acid . 75, 
Black oxide . 50, 
Sulphuric acid 154, 
Total 879 
Loss of weight 34-5 grains. It ought to 
have been 34.245 grains. Here the error is 
in excess, and.amounts to 0*255 grains. 
Experiment 3. 
Put into the flask — Water 600 grs. 
Oxalid acid 75 
Black oxide. 50 
Sulphuric acid 154*1 
Total 879*1 
Loss of weight 35 grains. Here also the 
error was in excess, and amounted to 0.755 
grains. 
