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 mangnesia 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 employed to decompose 

 carbonate of lime. 



In both forms of the apparatus, 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 drying tube ten inches long, occupied for an 

 inch at each end with dry cotton, and throughout the intervening 

 eight inches, with chloride of calcium properly desiccated. This, 

 supported in a horizontal position, is connected by a gum-elastic 

 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 for 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. 



