82 
Indian Forest Records. 
[Vol. IY. 
Action of crystalline alum .—The action of crystalline alum for 
clarifying rosin is remarkable. A small quantity of powdered 
crystalline alum when thrown into a hot liquid rosin pan held over 
an open fire, and stirred, gives rise to a brisk effervescence on 
account of the rapid escape of the water of crystallisation from alum. 
Alum losing its water of crystallisation rises to the surface in a 
spongy mass collecting in itself the suspended impurities of the 
rosin and removing its green colouration due to the traces of copper 
salt from the stills. The floating alum sponge is skimmed off, the 
rosin is then filtered through a fine sieve or cloth. From the alum 
residues pure alum can be recovered for further use. 
Commercial experiments at Bhowali. —The last mentioned 
method of clarifying rosin with crystalline alum appeared to be 
very suitable for application on a commercial scale. Accordingly, 
experiments on a large scale were tried at Bhowali in 1910, 
the results of which are tabulated below. The shellac merchants, 
to whom the samples of pale alum clarified rosin were sent for 
opinion, reported that it was desirable to impart to it a reddish 
tint characteristic of the imported colophony. As stated above it 
is not difficult to impart the required reddish tint to the pale 
variety. In pursuance of the wishes of the shellac merchants rosin 
of various shades was produced at Bhowali by clarification with 
crystalline alum or by varying mixtures of alum and nitre as will 
he seen from the table below: — 
Number. 
Description of the treatment. 
Colour as observed." 5 - 
A 
1 
Rosin | md. clarified with a mix¬ 
ture of 1 sr. alum crystalline and 
1 sr. nitre boiled together and 
filtered through cloth. 
Darkish red. 
B 
Rosin 1^ mds. boiled with 1 sr. of 
mixture of equal parts of alum 
and nitre filtered through cloth. 
! Transparent, reddish 
pale. 
C 
1| mds. rosin added to £ sr. nitre. 
Redder than B. 
D 
1£ mds. rosin added to \ sr. nitre. 
A slight reddish tint. 
[ 82 ] 
