ee ee ee ee eee a e 
A. McMayer on Weights of Small Portions of Matter. 39 
Art, IV.—The Estimation of the Weights of very small portions of 
Matter; by AtrRED McMayer, Professor of Physics and 
Chemistry in the University of Maryland. 
THE chemist, in the course of his analytical investigations, 
often meets with what are called traees of substances; y which 
is generally understood, quantities of matter too minute to have 
any appreciable weight in the analytical balance. Now it some- 
times happens that these traces are of as much importance con- 
sidered scientifically and commercially as the ingredients present 
i appreciable quantities; and in order to estimate these small 
portions of matter he is often obliged to go over his work, usin 
very considerable weights of substances, whereby his time I 
care are nearly doubled. It was this inconvenience that first in- 
duced me to try to determine in one operation the components 
peeut in large and in very minute quantities; and although I 
ave succeeded beyond my expectations, I am confident that the 
process is susceptible of improvement, both as regards sensibility 
and accuracy. a 
er making many investigations on the sensibility of the 
most delicate levers as to small weights, this method was found 
Tatus with which I have succeeded in estimating portions of 
matter equal in weight to the thousandth part of a milligram. 
Heating a rod of soft glass in one spot to bright redness, I drew 
it out quickly, and thereby obtained a, filament uniformly cylin- 
Cneal, of about the diameter of fine human hair. Taking from 
_ the middle of this fine glass thread a piece of such a length 
(about three inches) that its weight would barely reduce it from 
the horizontal, one end of it was fastened by means of goo 
Sealing wax to the edge of a Serer ar block, and the other end 
slightly hooked by approaching quickly a small spirit flame. In 
Oder to obtain a pan in which to place the substance whose 
Weight I would estimate, I eut with the common microscopic 
Section-cutter some disks of elder pith from ‘001 to ‘002 inch in 
thickness. and drawing out a still finer filament, the end was 
ewise hooked, and the other extremity being passed rer 
& pith disk, a small knob of glass was made on this end by the 
Spirit flame, just of sufficient size to prevent this disk slipping 
ree 
