by the Immersion of unequally Heated Metals in Liquids. 5 



varuish. There are also three leveling screws (of which only 

 two, J J, are shown) to enable the appai'atus to stand steady. 

 K is a bent copper pipe soldered to the copper cistern, and is 

 used to convey steam into the water. The cistern is provided 

 with a moveable half-lid of metal to admit of the insertion of a 

 thermometer, and to prevent the passage of the steam spilling the 

 water. 



10. In this apparatus the interference of contact of the atmo- 

 sphere is prevented ; the amount of immersed surface of each 

 piece of metal is kept perfectly uniform ; the temperature of the 

 heated metal is under almost perfect command, and is capable of 

 being very closely ascertained. 



11. AYhen it is used it is first taken asunder; the plates are 

 then perfectly cleaned by means of fine emery cloth [platinum 

 plates do not require this, but merely to be heated red-hot all 

 over), and repeated rubbings with clean cloths, each being made 

 exactly alike in smoothness and cleaned in a similar manner ; 

 they are then allowed to be face to face in contact with each 

 other for several minutes, to render them more perfectly alike in 

 temperature; the lower cylmder and its washers are also well 

 cleaned, distUled water being used for the washing operations. 

 It is then put together immediately, and the thumb-screws fixed 

 very firmly. 



12. The liquid to be examined being previously well boiled, 

 filtered, and cooled to the same temperature as the atmosphere 

 and apparatus, is then poured by the tube B into the cylinder 

 until the latter is quite full, and the tube filled to a level with 

 the top of the cylinder. All air-bubbles are excluded by shaking 

 the apparatus strongly whilst holding it in a suitable position 

 for their escape by the tube. 



13. The wires EE are now connected with the galvano- 

 meter, and the needles watched to see if any deflection arises 

 from a current of electricity produced by any difference of clean- 

 liness, smoothness, temperature, or other causes in the plates or 

 washers. If there is any permanent deflection, the apparatus 

 must be taken to pieces and rearranged : there is generally a 

 small temporary deflection even when all has been properly pre- 

 pared, especially with liquids which possess a strong atiiuity 

 for the particular metal in use ; but this does not materially in- 

 terfere with the result in ordinary cases, and may be safely dis- 

 regarded. 



14. The cistern F must now receive about three-quarters of 

 an ounce of water of exactly the same temperature as the innei' 

 liquid (the liquid having been previously put into a thin flask 

 and immer.sed for about ten or fifteen minutes in the water), and 

 the bulb of a thermometer placed in it. A current of steam 



