| 
ie ll 
saidiaiedianaiaaesaal 
Mr. Patten’s Air Pump, Gazometer, &ce 97 
poses, but not for weighing the gases and taking accurately 
specific gravities; and in analysis where the weights are 
often repeated it amounts to considerable. ‘The only ac- 
curate method is to make the weight ss the standard. (I 
believe a French proposition.) ‘To do this is the object 
of the beam ABC, (fig. 6th.) anuile of steel, suffi- 
ciently strong but light, the dish is suspended at A, the 
beam itself upon an axis at at C is the milled head of 
a long screw that is fitted ori a shoulder and axis, and 
goes through the slide E oe traverses upon BC and car- 
ries the weight D. Now suppose it is wished to obtain 
10 grains, place that weight in the dish F and screw 
back the weight D until it oeery counterbalances it— if the 
weight be now removed an uantity of the substance to 
be weighed be substituted atti the index points to where 
it did at first, there will then be very nearly aed exact 
weight with but small allowance for friction—for w 
beam a common one, and so nicely constructed as pe turn 
with the 100th part of a grain, it would by making the 
distance from AB four times greater than from B to D, 
the point of suspension of the weight—turn with the 400th 
part ofa grain. It is apparently an objection that 100 
rains at A will require 400 at D, but the fact is settled by 
outer’ that this kind of friction does not increase in an 
equal praporiion with the weights used, that is, if witha 
each scale, a beam turn with one grain, if there 
were ee pounds in ‘each, it would not require two grains. 
This beam may be used asa steel yard by screwing the 
weight D to any number marked upon the scale, an 
should a greater quantity be required than that marked in 
the first line, another weight double of D may be substi- 
tuted: These instruments are a few of a number I had 
occasion for while engaged in studies to which I was once 
particularly attached, but as they are in a great measure in- 
compatible with my professional occupation, I am 
in a great sete with relutasce to abandon them ; 
when leisure and d isposition a combine, I will send 
you, should you think they may he Ay any use to the schol- 
ar or'the analyst, some further communications, 
very Sa era 
your obd’t. s 
JOSEPH i PATTEN., 
Vo. (X.—No. 4 
