On the Fish-rod Balance. a 
Arr, IX.—Fish-rod Balance and Spheroidal Evaporation; by J. 
L. RmpELL, Prof. Chem. in the ‘Med. Dep. of the Gaiwonaey 
of Louisiana. 
Messrs. Epirors: 
I HAVE read an article in your number for Jan 1858, p. 
89, by Prof. Alfred McMayer, on “the estimation of the weights 
of very small portions of matter.” That he independently in- 
vented the instrument therein descri I have no reason to en- 
tertain Siem In 1840, while residing at the U.S. Branch 
mint of this city, I invented, constructed and used a similar 
contrivance. I called it the fish- red balance. I Sara a mi- 
nute tapering hollow tube of glass, mounted it adjustable in a 
glazed case to avoid drafts of wind, suspended from the small 
= free end an extremely light pan by a thread of glass, ter- 
nating in an indicator point, the point traversing over a mi 
schclter scale, a view of which was commanded by a micro- 
scope. Values were written upon the scale from observation, at 
intervals, and carried out by interpolations. I operated more or 
less with this instrument for six years, during which time it was 
See by hundreds of persons now living. Prof. McMayer 
er-estimates its delicacy and over-estimates its reliability. 
’ The purpose to which I mostly igus it, was to determine 
the amount of non-volatile oe in Tr 
ment it was skillfully tossed into a clean porcelain capsule, and 
presented the earthy and saline residue in the form of a minute 
—— generally too minute to be he oe in an assay balance. 
cations of weight, from the effects of varying temperature, f 
m ar changes in the glass becoming manifest in Gave aa 
robably ag other causes which I did not investigate. Hence 
F came to think little of it as an accurate means 0 of de etermining 
minute weights, and much of it as a probable s of investi- 
gating the oa ws of molecular chang: ef 6 vein Af inquiry 
which as yet I ate Sas 
New Orleans, April 17, 1858. 
