A text-book on chemistryFor the use of schools and colleges . iquid thermometers can not measure the highestdegrees of temperature, because the vaporization of theircontents would cause their destruction. For this reason,the expansion of one of the more infusible solids, as, forexample, platinum, must be used, and some contrivancesimilar to Fig. IS employed. The difficulty with suchapparatus is that the expansion of a short bar of metalis so minute that some means of magnifying the effectis necessary, and at once irregularity is introduced bywheel-work and friction of levers. A compound stripo
A text-book on chemistryFor the use of schools and colleges . iquid thermometers can not measure the highestdegrees of temperature, because the vaporization of theircontents would cause their destruction. For this reason,the expansion of one of the more infusible solids, as, forexample, platinum, must be used, and some contrivancesimilar to Fig. IS employed. The difficulty with suchapparatus is that the expansion of a short bar of metalis so minute that some means of magnifying the effectis necessary, and at once irregularity is introduced bywheel-work and friction of levers. A compound stripof metal is free from these difficulties, and will, if longenough, indicate temperatures writh great thermometer consists of a delicate slip of What are Ruperts drops? Do solids expand equally in all di-rections? Describe the effect of heat on calcareous spar. Statethe peculiarities of fusible metal when heated. For what purposesare liquid thermometers inapplicable ? What is the difficulty withsolid thermometers ? 30 METALLIC platinum soldered with gold to oneof silver, and curved into the formof a spiral, a 5, Fig. 20. It is fast-ened at its upper end to a metallicsupport, e c, and from its lower endan index projects, which plays overa graduated circle. As silver ex-pands twice as much as platinum,when the temperature rises, curva-ture, with motion of the index,takes place ; when it falls, motion in the opposite direc-tion results. The principle is the same as that describedin the case of the compound bar, Fig. 19. This ther-mometer is exceedingly rapid in its indications, becausethe mass of the spiral is so small, as compared with themercury in the bulb of a thermometer. By breathingupon it, it will in an instant rise to above 90°. For the highest temperatures Darnells- pyrometer isemployed. It consists of a bar of platinum inclosed ina cylinder of black-lead earthenware. When it is heat-ed, as the platinum expands more than the earthenware,i
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