352 Professors W. B. and R. E. Rogers 
thirds of its length. With these precautions, we have found the © 
acid to be retained in the bulb, without the slightest tendency 
to drop. The drying tubes belonging to this form, are both 
bent horizontally, and inserted, the one through the cork of the 
bottle, the other through that of the pipette. This form of the 
instrument we use for such carbonates as are very hygrometric, 
and could not therefore be weighed in the bucket, and also for 
such as are very bulky, as those of magnesia and zinc. We — 
have moreover found it more convenient than the other, where 
the compound formed by the reaction is insoluble, and forms a 
pasty mass, as when sulphuric acid is emiployed to decompose 
carbonate of lime. 
In both forms of the acheive, the outside of the bottle, pi- 
pette and drying tubes, should be well coated with a smooth var- 
nish of shell-lac, and the corks, and especially that of the bottle, 
should be repeatedly coated and dried, so as to be well imbued with 
the varnish for some depth. This is so important a precaution, 
that unless the large cork happen to be uncommonly close in 
texture, the permeation through it, in experiments of long con- 
tinuance, is capable of producing very serious errors. 
To the parts here described, which in both forms compose the 
apparatus proper, certain appendages are added in the course of 
the experiment. These, as shown in fig. 2, to the left and right 
of the decomposing bottle, are as follows. 
First.—A large degine. tube ten inches long, occupied for an 
inch at each end with dry cotton, and throughout the intervening 
eight inches, with chloride of caleium properly desiccated. This, 
supported in a horizontal position, is connected by a gum-elasti¢ 
tube with the little supplemental bent portion of the upright dry- 
ing tube. It is made thus long to ensure the absence of moisture 
in the air drawn into the apparatus, in the process of aspiration. 
Second.— An arrangement Sor aspiration, consisting of a three 
necked Wolfe’s bottle, holding about fifty cubic inches, to which 
are adapted a long glass syphon on the one side, a bent connect- 
ing tube on the other, and a ground stopper in the middle aper- 
ture. The bottle being filled with water, the syphon is made to 
operate by applying the lips below, and a stream of dry air is 
drawn into and through the apparatus, as long as the water contin 
ues to flow. A short tube drawn to a small orifice and made to 
fit over the end of the syphon, or what is better a small stop-cock, 
may be used to regulate the stream. 
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