178 Mr. Carl Barus on the Fusion 



air-blast, laden, if need be, with oxygen. These burners are 

 placed at equal intervals along the vertical, three on one side 

 and three on the other (see fig. 2), and set like a force-couple, 

 so as to surround the platinum tube with a whirlwind of flame. 

 Suitable holes are cut in the walls of the furnace for the sym- 

 metrical insertion of the insulated thermocouples, T, and also 

 at S for fixing the sight-tubes, A, near the top and the bottom 

 of the furnace. Parts of the envelope of the platinum tube 

 are cut away, so that the upper and lower ends of the (red 

 hot) platinum tube can be seen in the telescope of an external 

 (screened) cathetometer. Thus the expansion of the platinum 

 tube is measured directly. A vertical micrometer, ~Kkd 

 (figs. 3 and 4), insulated so as to admit of electrical indica- 

 tions of contact, furnishes a means of tracing the apparent 

 expansion of the rock Z Z, within the fusion-tube. 



In principle, the excessively slow cooling of the furnace is 

 to be so conducted that the magma may always remain much 

 less viscous than the practically rigid platinum envelope 



(§§ 1, 18). 



The furnace stands on a massive iron base perforated by 

 eight holes, into which vertical iron uprights are screwed, 

 symmetrically surrounding the furnace and at a distance of 

 4 or 5 centim. from its circumference. Only one of these 

 is indicated at Q Q (fig, 3), the rest with other subsidiary 

 parts being omitted to avoid confusing the figure. Two of 

 these uprights hold the vertical micrometer, two hold the 

 burners in place, and two subserve as buffers for the clay 

 arms, H, H, . . . by which the fusion-tube is adjusted verti- 

 cally. The sight-tubes are suitably clamped to the seventh 

 and the insulators of the thermocouples to the eighth. All 

 these uprights are hollow, and a swift current of water con- 

 tinually circulates through them, issuing still cold to the 

 touch. The same current also flows through the bent screen, 

 X X, of the vertical micrometer, and through the vertical flat 

 screen of the cathetometer. 



6. The Furnace. — The burners, B, are each fed with the 

 same amount of gas and air by properly branching the large 

 supply-tubes. A graduated stopcock is at hand for regulating 

 the supply of gas to a nicety. Hence the furnace is fed with 

 a mixture of gas and air, and temperatures between 400° and 

 1500° are obtained by simply making the influx poorer or 

 richer in combustible gas. Oxygen has not thus far been 

 necessary*. 



< * Burners suitable for the above purpose are shown in my little book 

 on high temperatures (Leipzig, Barth, 1892). 



