1870.] 



Mineral Constituents of Meteorites. 



147 



II. On the Method of Analyzing Silicates that do not gelatinize with 

 Hydrogen Chloride. 



The process is conducted in an apparatus of the following construction. 

 A platinum retort, 30 cub. centims. in capacity, is fitted with a tubulated 

 stopper of the same material, which reaches nearly to the bottom ; a small 

 tube entering the vertical tube of the stopper at an angle, above the neck of 

 the retort, conveys hydrogen to its interior. The vertical tube can be 

 closed either by a stopper of platinum or by a funnel of that metal, stopped 

 in like manner at the top, and having a fine orifice at its lower extremity. 



To the side of the retort, just below its neck, a straight delivery-tube is 

 fixed, which in its turn fits into another platinum tube that, after taking a 

 curve into a vertical position, is enlarged into a cylinder, which passes a 

 considerable distance down a test-tube. The latter, into which the de- 

 livery-tube is fitted with a cork, holds 7*5 cub. centims., or 6*6 grammes 

 of strong ammonia of the spec, gravity 0*88. 



The gas-delivery tube inserted in the side of this receiver dips into some 

 more ammonia in a second test-tube. 



The pounded mineral, from 0'2 to 0*5 gramme in quantity, and a small 

 platinum ball, are placed in the retort, and the stopper luted to it with 

 gutta percha, and cemented air-tight in its place with caoutchouc and gutta- 

 percha varnish. The funnel, filled with perfectly pure hydrogen fluoride, 

 is now introduced into the tubulure of the stopper, the tap opened, and 

 the acid allowed to run down into the retort. This acid contains about 

 32 per cent, of absolute hydrogen fluoride — that is to say, a funnel of this 

 reagent contains 1*12 gramme of acid, capable of rendering gaseous 0'84 

 gramme of silica, and of neutralizing 0*95 gramme of ammonia. The 

 funnel is now replaced by a little platinum stopper, and the orifice secured 

 air-tight with gutta-percha varnish. Pure hydrogen is then allowed 

 slowly to traverse the entire apparatus, the retort is placed in a water-bath 

 at 100°C. for two hours, and occasionally slightly shaken to set the ball 

 rotating. During the operation a trace only of silicium difluoride passes over, 



The retort is next transferred to a paraffin-bath, and the temperature is 

 cautiously raised. At first hydrogen fluoride passes over, and at this point 

 of the process the flow of hydrogen requires some attention to prevent 

 regurgitation of the ammonia. At about 132° C, in the case of the sili- 

 cates mentioned in this memoir, the silica first becomes visible in fine flocks 

 in the ammonia of the receiver, and in another minute the whole is cloudy. 



In eight minutes the rise of the thermometer to 145° C. has brought 

 over so much difluoride that the contents of the tube are semisolid, and 

 nearly the whole of it has passed over. The temperature is then raised to 

 150° C, and the retort allowed to cool. The process is next repeated with 

 a fresh charge of acid and ammonia. If no more than 0*2 gramme of 

 silicate be taken, twice charging of the retort is sufficient ; but with 0*5 

 gramme three or four repetitions of the process are required. In short, 

 the operation is continued with fresh reagents till no flock of silica forms 



VOL. XVIII. M 



