404 K T. Allen, F. K Wright and J. K. Clement- 

 is very nearly equal to that of the orthorhombic amphibole 

 {/3 = 1*585), while tbe birefringence is not strong and is of the 

 same order of magnitude as that of the orthorhombic form. 

 The crystals, like those of the orthorhombic amphibole, are 

 not so clear and transparent as the higher refracting pyrox- 

 enes, often showing distinct lines of growth ; the twinning 

 lamellae are usually fine and less sharply defined than in the 

 monoclinic pyroxene. Intergrowths of the orthorhombic and 

 monoclinic amphiboles were also observed occasionally, though 

 they were distinguished with less certainty than in the pyrox- 

 enes. 



The change of the orthorhombic to the monoclinic amphi- 

 bole with water at temperatures of 3 / T5 -475° did not yield 

 any well-formed crystals ; the product appeared to be rather 

 the result of a paramorphic change in the solid state. In the 

 hope of getting individually developed crystals, we attempted 

 the synthesis of this form from magnesium salts and soluble 

 silicates or silica, and succeeded in getting a product with 

 optica] properties similar to those of the magnesian amphiboles, 

 but in fibers so small that it was impossible to say whether 

 they were orthorhombic or monoclinic. In view, however, of 

 the partial change of the former into the latter, it seems 

 probable that they were monoclinic. 



Experiments in the Synthesis of the Amphibole at Low 

 Temperatures. — Chrustschoff, some years ago, published a 

 description of a method for the formation of hornblende in 

 which a mixture of silicic acid, alumina, lime, magnesia, fer- 

 rous and ferric oxides, and the alkalies, partly in solution, 

 partly precipitated, were heated in sealed glass vessels at a 

 temperature of 550° for three months.* 



It seems to us that glass vessels of such extraordinary proper- 

 ties deserve to be better known, and that the experimenter should 

 have given some details concerning them, especially where 

 they can be obtained, together with some information about 

 his temperature measurements. 



The experiments which we shall describe were done in a 

 steel bomb 16 cm long, 2 , 7 cm internal diameter, and l*4 cm thick, 

 which was made by boring out a piece of steel shafting. The 

 bomb was closed by a plug also of steel having a total length 

 of 8 cm , the screw of which was 4 cm in length and fitted into a 

 thread cut in the end of the bomb. A tight joint was insured 

 by a washer of annealed copper 3 or 4 ,nm thick. The steel sur- 

 faces in contact with it were planed smooth, and into each 

 were cut a number of very narrow concentric grooves about 

 half a millimeter deep. To close the bomb, the plug was 

 *Comptes Rendus, cxii, p. 677, 1891. 



