Annual Meeting.] 344 [May 2, 



{Label.) 



Magnetism Series. 



Showing that the magnetism of the few magnetic minerals is 

 proportional to the percentage of iron they contain. 



Limonite, iron 60 pr. ct., never magnetic. 



Hemstite, iron 70 pr. ct., sometimes magnetic. 



Magnetic, iron 72.4 pr. ct., always magnetic. 



(e). The relations of water in the composition of minerals are 

 dealt with in a series running from a strictly anhydrous Hema- 

 tite to Natron (Hydr. Carb. Sodium) having 55 per ct. of water. 

 There are twelve specimens in this series, and behind each speci- 

 men a tube shows the relative proportion of water in each. 



(2nd). Form and structure, or crystallography, presented no 

 very serious difficulties beyond the need of finding persons capable 

 of making the special models which were required. This was fin- 

 ally satisfactorily accomplished. 



(3rd). As an example of the methods pursued in illustrating 

 the Physical Properties of Minerals, we give the following 



(Label.) 

 Density Series. 



Showing the range of minerals in specific gravity. 



(a). This series consists of twenty-seven minerals, from Gold 

 which is twenty times heavier than water, to Petroleum, which 

 is lighter than that standard liquid. This gradation is made appar- 

 ent to the eye by means of glass tubes containing equal weights 

 of each of the substances, the solids being l educed to a fine 

 powder. Thus Gold, with Sp. Gr. 19. 5, the heaviest substance, 

 has necessarily the shortest tube, and Petroleum with Sp.Gr. 0.75, 

 the longest tube, and the intermediate tubes show the gradations 

 between these two. A series is formed in this way, which exhibits 

 clearly that the volume of minerals is inversely proportional to 

 their specific gravity, or weight. 



There are a number of series showing the relation of minerals 

 to light, among which we may select by way of illustration that 

 of the color test or streak of minerals. 



