Description of an Universal Hydrometer . 469 
their ill effects the arch or dome over the feeding hole 
is erected to carry the fume into the stack of the fur- 
nace. 
NO. 90. 
Description of Mr. G. Atkins’s Hydrometer for deter- 
mining the Specific Gravity of both Solids and Li- 
quids.* 
(With an engraving'.) 
SIR— The present improved state of chemistry ; its 
application to so many of our principal manufactures, 
and the necessity of determining the specific gravity of 
the various substances which are used in them, or afford- 
ing in all cases an important indication with regard to 
their qualities, and being in many the only accurate mea- 
sure of their value, may perhaps render the following de- 
scription of an instrument for this purpose not unaccept- 
able to your numerous readers. 
By giving it a place in your valuable Magazine you 
will therefore oblige yours, &e. 
George Atkins, 
To Mr. Tilloch. 
Fleet Street , September 10 , 1808. 
The specific gravity, or comparative weight of the 
majority of those substances which fall under the obser- 
vation of the manufacturer, the mineralogist, or the che- 
mist, having always been considered as one of their most 
distinguishing characteristics, a variety of methods 
Tilloch, vol. 31, p. 254. 
