a Professors W. B. and R. BE. Rogers * 
cork, flask, pipette and drying tube are coatéd with a varnish of 
3 + shell-lac, to protect the cork from infiltration, and to diminish the 
 hygrometric action of the surface generally. 
In using the instrument, a weighed quantity, say 40 grains, of 
the carbonate is placed in the flask, and if it be in powder, enough 
water is added to moisten it throughout. The pipette is then 
charged with hydrochloric or sulphuric acid, by placing its open 
end in a capsule containing this liquid, compressing the gum-elas- 
tic bag, and then allowing its elastic expansion to pump the acid — 
into the bulb. Sometimes the pipette thus charged, when held 
upright, permits the liquid slowly to accumulate in a drop, at its 
beak, thus endangering a premature descent of the acid upon the 
carbonate, which would vitiate the experiment. This is effectu- 
ally prevented by lightly pressing the bag and allowing it to re 
coil so as to draw a short column of air into the tube, near the 
end. he cork bearing the pipette and drying tube, being then 
secured in the flask, the acid will remain supported without any 
tendency to ooze out, and the instrument is in a condition to be 
placed in the balance to be counterpoised. This done it must be 
removed and placed upon a clean dry surface, near the balance, 
where, gently pressing the bag, the acid is to be projected in @ 
- fine stream on the carbonate, the action being regulated so as t0 
maintain a steady but not too violent effervescence. When all 
the carbonate has been decomposed, which in the case of a matl” 
or limestone occupies but a few minutes, the acid still in the 
bulb must be expelled into the flask. 
To remove the carbonic acid remaining in the instrument aftet 
the completion of the reaction, a large drying tube must be alr 
nexed to the end of that belonging to the apparatus, and the gum 
elastic bag must then be made to operate as a pump, by alternate 
compression and dilation. Continuing this action for some time, 
the gas is in great part if not wholly expelled, while the air e0- 
tering from without at each alternation of the movement, deposits 
its moisture in the large drying tube, instead of adding it to the 
weight of the apparatus, as it would were this appendage omit- 
ted.* The second weighing is now performed, and the loss of 
ae 
* The error here adverted to, must also arise in the use of Rose’s apparatus, 
whenever, as Parnell directs, heat is applied to expel the carbonic acid remaining 
at the close of the action. For the air entering as the flask grows cool, must in- 
crease the normal weight by the amount of moisture it contains. = 
