142 RE-EXAMINATION OF AMERICAN MINERALS. 



ically from the gangue made it very evident that the mineral 

 was more or less mixed with other substances which had es- 

 caped observation, for no two analyses agreed; and it was soon 

 discovered that it was impossible (from the specimens in my 

 possession at least) to separate boltonite in a state of purity 

 without the aid of other means than had been adopted. 



Boltonite, as is well known, occurs at Bolton, Mass., dissem- 

 inated in irregular masses and grains in a white limestone. 

 If a piece of the mineral in its gangue be placed in cold dilute 

 hydrochloric acid, the limestone is readily dissolved and a mass 

 left which is seen to consist of asbestus, dolomite, a little mica, 

 small crystals of magnetic iron, and a greenish or yellowish- 

 green mineral; if the acid be now heated, the dolomite will be 

 entirely dissolved with a little of the last-mentioned mineral. 



In order to obtain the boltonite as pure as possible for 

 analysis the following method was adopted. Pieces were sepa- 

 rated by the hammer as thoroughly as possible from all other 

 substances ; these were subsequently placed in dilute hydro- 

 chloric acid and boiled for some time ; the acid being washed 

 away and the substance dried, it was crushed in a mortar to 

 fragments from the twentieth to the tenth of an inch in diam- 

 eter ; these were again introduced into dilute acid and heated 

 for a short while ; the acid was thoroughly washed away and* 

 the mineral dried. The small fragments (now like coarse 

 gravel) were placed on a piece of glazed paper, the hand laid 

 flat upon it, and the mineral rubbed so as to grind the parti- 

 cles against each other for the purpose of ridding their surfaces 

 of a little cohering silica arising from its partial decomposition ; 

 with a small gauze sieve the finer particles are separated, and 

 from that remaining in the sieve we are enabled with the aid 

 of a glass without any difficulty to pick out the pure boltonite. 

 This method requires a little patience, but no extraordinary 

 care ; and, however unj^romising the original specimens may 

 have been, there is no difficulty in obtaining a material the 

 results of whose analysis are constant. From a larger selec- 

 tion of specimens than that used there doubtless could be 

 obtained pieces, perfectly pure, of some size. After being 

 satisfied with this method of obtaining the pure mineral, 

 three different portions were prepared and examined, the 

 first two being of the greenish variety and the third of the 



