354 Professors W. B. and R. E. Rogers 



very uniform temperature, so as to dispense with any rubbing of 

 the apparatus before weighing, a proceeding which though com- 

 monly practiced, frequently leads, according to our observations, 

 to much uncertainty in the subsequent counterpoising. This re- 

 sult is in part due to the deposition of moisture on the apparatus, 

 in the act of weighing, which even in a uniform condition of the 

 air as to humidity, must be unequal in the first and last weigh- 

 ings, unless the temperature of the vessel, and the time consum- 

 ed in the process, be the same in both cases. But a still larger 

 share of the effect is chargeable, according to our experiments, to 

 the electrical excitement produced in the glass by the friction, 

 which, communicated to the scale pan, affects the apparent weight. 



We will now briefly sketch our mode of using the apparatus 

 in exact research, and describe a further process, which we have 

 found necessary for expelling the carbonic acid from the liquid. 



When the bucket is used, a small bit of tissue paper is pressed 

 down upon its bottom, so as completely to close the hole, and 

 then the weighed carbonate, usually one hundred grains, carefully 

 transferred into it. Having charged the bottle with moderately 

 dilute hydrochloric or sulphuric acid, in quantity a good deal 

 more than is required to neutralize the carbonate, and having 

 properly adjusted the cork, we hang the bucket with its contents 

 upon the upper hook of the platinum wire, and lifting the appa- 

 ratus into the scale by the buckskin holder, we counterpoise it 

 with great care. Then withdrawing it from the scale, we lift 

 off the bucket, remove the cork, attach the bucket to the lower 

 hook, previously drawn up so as nearly to touch the lower side of 

 the cork, and again secure the cork in its place. As it now hangs 

 the bucket is from one half to three fourths of an inch above the 

 level of the liquid. Depressing the wire, we plunge the bucket 

 into the fluid, which enters by the aperture below, and varying 

 the depth of immersion from time to time, we regulate the effer- 

 vescence, so as to be uniformly brisk, but without great violence. 



The effervescence having ended, as shown by the absence of 

 any crepitation when the ear is held close to the flask, the liquid 

 is briskly agitated to favor the escape of adhering bubbles, and 

 the instrument is now connected with the appendages above de- 

 scribed, in the manner indicated in fig. 2. The syphon being 

 set in action, and the closeness of the connection ascertained, as 

 before directed, the aspiration is commenced. During this pro- 



