of the PyroUgnous Acid. S7 
The method which I followed in purifying the brine was 
simply as follows : It was diluted with water to the specific gra- 
vity of I 5 I 6 O 5 and then put into a clean cast-iron boiler. For 
every thirty gallons of English wine measure, a dozen of eggs 
were beat up and mixed with the brine ; at the same time, about 
half a pound of fine ground charcoal was also put into the boiler, 
and the whole well stirred together. The brine being now be- 
low saturation, when heated, allows the impurity contained in it 
to rise to the surface, and when brought to boil, is carefully 
skimmed off. The liquid on cooling is now as pure as water. It 
is well known that charcoal imbibes putrid efiluvia. This sub- 
stance frees the brine from its offensive smell, and at the same 
time the eggs coagulating, carry off the charcoal and impurities 
of the brine entirely to the surface. On again packing the 
herrings, a very small portion of salt is strewed on them, so that 
the brine may again become saturated ; and the brine, when 
cooled, is poured into the cask until the fish are covered by it. 
The very respectable dealer whom I directed to the above 
process for clarifying brine, has frequently told me, that, since 
he adopted it, he has never had a complaint against the her- 
rings ; and, as a proof of -this, he disposes of several thousand 
barrels yearly. 
Qlasgow, March 1820. 
Art. III . — On the Length of the Pendulum.^ in reply to a Let- 
ter contained in No. XVI. of the Quarterly Journal of 
Science^ By William Watts, Esq. 
I Feel myself called upon to notice certain observations con- 
tained in a letter which has appeared in No. XVI. of the Quar- 
terly Journal of Science, Literature, and the Arts,” under the 
signature of Z, relative to my remarks on Captain Eater’s Pa- 
per containing Experiments for determining the length of the 
Seconds Pendulum in the latitude of London; because this 
critic has thought fit to give a very partial and unfair out- 
