12 Chemical Examination of American Minerals. 



lime, differs so much in the quantity of earthy matter which 

 it contains, that no two filters, though made of the same 

 weight, would be found corresponding in this respect. By 

 digesting the filtering paper in diluted nitric acid, and then 

 washing and drying it, I easily get rid of the lime, which has 

 probably been introduced during the bleaching of the rags. 

 The inequality of the earthy matter contained in the washed 

 paper, makes it impossible to estimate the weight of the 

 powders collected on the filter, by burning it and weighing 

 the ashes, as is done by the chemists on the continent of 

 Europe. I have been obliged to have recourse to the fol- 

 lowing method, which however is sufficiently accurate. Two 

 filtering papers are made of exactly the same weight, by 

 balancing them against each other in a pair of scales, and cut- 

 ting off pieces with a pair of scissors from the heaviest filter, 

 till it is brought precisely to the same weight as the other. 

 These two filters are placed one within the other, and the 

 matter whose weight I wish to ascertain, is collected on the 

 innermost one, by pouring the liquid in which it is contained 

 into the filter. When the liquid has run off and left the silica, 

 distilled water is to be poured over it, and this must be re- 

 peated till the silica be quite clear. 



This process of washing deposits upon filters, is one of the 

 most important parts of a chemical analysis. It is requisite 

 that not merely the matter collected at the bottom of the filter 

 should be clear, but that every thing soluble should be washed 

 out of the filter itself. This is best done by means of the 

 little instrument represented in the margin, which I 

 call a sucker. It consists of a glass tube about a foot 

 long, terminating below in an opening almost capil- 

 lary, and having a portion about three or four inches 

 from the top, blown into a globular cavity. This 

 sucker is dipt into distilled water, and by the action of 

 the mouth, water is drawn in till the globular cavity 

 is filled. This water is then forced by the pressure 



