Minerals of the Composition MgSiO z . 405 



screwed in by a long heavy wrench until the copper filled the 

 grooves. A new washer should be used for each experiment. 

 The capacity of the bomb was great enough to admit a cylin- 

 drical platinum crucible holding about 30 cc . Temperature 

 measurements were made by introducing an insulated thermo- 

 element into a 7 mm hole in the plug, the end of which it 

 reached within 5 mm . The source of heat was aBunsen burner. 

 To distribute the heat more evenly, the bomb was surrounded 

 by a collar of asbestos and sheet iron with a hole on the under 

 side through which the flame passed. The joint was shielded 

 from the latter by an annular asbestos disk which was slipped 

 over it. 



For the synthesis of the amphibole, the magnesium was 

 taken in soluble form, either magnesium-ammonium chloride 

 or a mixture of magnesium chloride with a sodium bicarbonate 

 solution ; while the silica was used in the amorphous state or 

 in combination as sodium metasilicate. Generally *25 or -50 

 gram of magnesia was dissolved in the equivalent quantity of 

 hydrochloric acid, then the ammonium chloride or sodium 

 bicarbonate was added, and finally the silica or sodium silicate. 

 This mixture was poured into the platinum crucible with 25 cc 

 or more of water, covered, and put into the bomb, which was 

 then closed tight and heated from 3 to 6 days at temperatures 

 ranging from 375° to 475°. Although in the course of these 

 experiments the details were varied considerably, w T e were 

 only able to ascertain that the products formed at the higher 

 temperatures were usually better crystallized. 



When the bomb was opened, it generally contained more or 

 less water, sometimes several cc. ; the inner wall of the bomb 

 itself was coated with magnetite, and sometimes the platinum 

 crucible was covered with beautiful octahedra of the same 

 mineral. In some experiments in which the water was nearly 

 all gone, the bomb showed when cold an internal pressure and 

 the odor of ammonia was noticeable. 



After removal from the bomb, the products were washed 

 and dried. To the naked eye they were all much alike ; they 

 were white, and of a tough and spongy texture. Optically 

 they left much to be desired. 



They were mostly crystalline but invariably fine-grained, 

 often cryptocrystalline, and had to be studied rather in the 

 aggregate than in individual fibers. In all these preparations 

 the substance present in predominant quantity consisted of 

 complex groups of fibers which extinguished parallel to their 

 elongation, this direction being that of the least ellipsoidal 

 axis c ; their refractive index was less than 1*60 and agreed 

 with that of the magnesium amphibole, so far as such minute 

 fibers admit of measurement. The birefringence was low. 



