400 On unequallj/ heated Mercury and Fluid Alloys. 



Y^th of an inch in diameter ; M is supported at its outer end by 

 means of a cork, N, and a piece of bent sheet brass, O (see 

 fig. 3), fixed in the tube C". P is a small moveable wooden screen, 

 3 inches wide and 3| inches long, supported by means of a wire 

 (with a handle, Q), which passes first in a vertical direction 

 through the cork D, and then horizontally outwards beneath two 

 small wire hooks fixed in the upper and back side of the screen. 

 R and R' are two small solid stem-thermometers with cylindrical 

 bulbs, supported in the necks of the glass vessels by means of 

 closely-fitted and perforated corks ; the cork of the flask G has a 

 small notch cut in its side to allow expanded air to escape. S is 

 simply a small spirit-lamp capable of being moved with its stand 

 T, either vertically or horizontally, by means of the tube C. 



Mode qfusinff the Apparatus. 



Take about half an ounce by measure of clean mercury, or of 

 the fluid alloy under examination, pour a portion of it into the 

 outer end of the tube M until it acquires the level U in the 

 bulb G, and pour another portion into the outer end of the tube 

 J until it attains a similar level. 



The liquid to be examined having been filtered and recently 

 boiled to expel dissolved air, and cooled to the atmospheric t'em- 

 perature, is poured into the large tubulure of F (the thermometer 

 having been previously removed) until the level V V in the two 

 vessels is attained ; the thermometer is then replaced air-tight. 

 The extreme ends of mercury in the tubes J and M are now 

 connected by wires, W W, with a galvanometer, and the appa- 

 ratus allowed to remain at rest until the needles return to zero. 

 Heat is now applied to G very gradually by means of a very 

 small flame of a spirit-lamp, the latter being in its lowest posi- 

 tion, and is gradually increased by slowly raising the lamp-stand, 

 — the deflexions, their amount and direction, and the temperatures 

 of the contents of the bulbs being recorded at intervals until the 

 liquid in G approaches its boiling-point. The heat is efiiectually 

 excluded from passing to the vessel F by means of the inclined 

 position of the connecting tubes I and K, also by means of the 

 screen P. 



If the liquid is not pre-boiled, interferences are produced by 

 the development of air-bubbles upon the surface of the metal in 

 G at the higher temperatures. If the heat is applied too sud- 

 denly, the apparatus is endangered ; and if applied too rapidly 

 at the higher temperatures, large bubbles of vapour are formed 

 at the lower surface of the mercury. If by long-continued 

 action heat is suspected to pass by conduction to the outer end 

 of the mercury in M, a small piece of damp cloth may be placed 

 about mid-distance upon that tube. If the corks surrounding 



