on the Analysis of the Carbonates. 353 



Third, — A test bottle, containing a solution of nitrate of silver, 

 placed between the decomposing vessel and the instrument for 

 aspiration. This appendage is introduced in the figure and refer- 

 red to here, not because we deem it essential, when the operation 

 is conducted with even common care, but as necessary to com- 

 plete the picture of the apparatus of research, as used by us in 

 our experiments. It will be shown hereafter, contrary to the inti- 

 mation of Erdmah and Marchand, that hydrochloric acid does not 

 pass through the drying tubes, either in company with the stream 

 of evolved carbonic acid, or during the aspiration with the air. 

 As however an extreme violence in the effervescence, accidental- 

 ly occasioned, might cause some of it to escape, a fact not yet 

 witnessed in any of our experiments, we continue to use this ap- 

 pendage as a sentinel to give us notice of the error. 



In adjusting the apparatus for use, great care should be taken 

 to make all the connections, from the remote end of the large 

 drying tube, to the short tube of the test bottle inclusive, perfect- 

 ly air tight. To be sure of this, after putting the parts together, 

 the end of the drying tube should be closed by a little fragment 

 of soft cement, then setting the syphon in operation, if the junc- 

 tions referred to are perfectly close, the stream of bubbles rising 

 through the solution of nitrate, will soon entirely cease. The 

 importance of this air-tight connection, will at once appear from 

 considering that during the aspiration, the smallest opening in 

 the corks or gum-elastic tubes of the decomposing bottle and its 

 drying tubes, by giving admission to air from without, must in- 

 crease the weight of the instrument, by the amount of moisture 

 it brings with it, an increase which even in a seemingly tight 

 condition of the apparatus, when the above precaution was not 

 used, has in some of our experiments amounted to two one-hun- 

 dreths of a grain. 



To facilitate the removal of the apparatus, proper for its con- 

 nection, previous to the second weighing, the binding string 

 should be fastened by loop- knots with long ends. This caution, 

 however insignificant it may appear, is necessary to prevent the 

 handling of the instrument, and to avoid any loosening of the 

 corks. It may also be added, that in moving the instrument to 

 or from the scale, it should be held by the horizontal tube, be- 

 tween the folds of a piece of clean buckskin. For accurate re- 

 search, the experiments should be made in a dry atmosphere, of 



Vol. xlvi, No. 2.— Jan.-March, 1844. 45 



