. Practical physical chemistry . the conical connecting piecein the side of the prism case, and the thermometer screwed The glass cell may be cemented to the prism by means of fish-glue orseccotine, the cement being applied in a thin uniform layer to the edge ofthe glass cylinder. This is facilitated by means of a glass block, the surfaceof which is ground so as to have the same curvature as that of the edge ofthe cylinder. The cement is first rubbed on the surface of the block, andthe edge of the cylinder then placed on the block and carefully turned roundso as to apply a thin coating of ceme
. Practical physical chemistry . the conical connecting piecein the side of the prism case, and the thermometer screwed The glass cell may be cemented to the prism by means of fish-glue orseccotine, the cement being applied in a thin uniform layer to the edge ofthe glass cylinder. This is facilitated by means of a glass block, the surfaceof which is ground so as to have the same curvature as that of the edge ofthe cylinder. The cement is first rubbed on the surface of the block, andthe edge of the cylinder then placed on the block and carefully turned roundso as to apply a thin coating of cement. When the temperature of the experiment is not high, the cell may fre-quently be attached to the cylinder by means of vaseline. In this case,however, it is very easily displaced. In this, as in all such cases, only a very gentle pressure must beexercised in lightening the screw. 102 PRACTICAL PHYSICAL CHEMISTRY into the top of the heater. Water from a thermostat canthen be caused to circulate round, the prism and through the. Fig. 34. heater (S), the water being passed in at L, and allowed to runto the waste through the tube connected with the heater. OPTICAL MEASUREMENTS 103 The light, after refraction through the prism, passes intothe telescope tube through an elongated oblong slit in thecap F. This can be rotated through a certain angle, but thereare four points at which it is fixed by stops, the action of whichwill be felt on rotating the cap. In one position the whole ofthe oblong slit is open to the prism, in two other positionsonly half the slit is open, while in the fourth position theaperture is closed altogether. The half-slits are used onlywhen observations are being made with a divided cell; whena single cell is used, the whole slit must be open. On examining the face of the disc D, to which the telescopeis attached, it will be seen that it is graduated over a quarterof its circumference into degrees and half-degrees (30); andthere is a vernier with thirty divisi
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