VOL. LII.] PHILOSOPHICAL TRANSACTIONS. 54^ 



effects were always produced, making an allowance for the different contraction 

 of the different glasses, under so severe a degree of cold. But if these tubes were 

 filled with different mercury, there was then a sensible difference ; inasmuch as , 

 mercury revived from sublimate did not subside so fast in the thermometer as 

 that did which was less pure. He has even found, that he has been able to con- 

 geal the less pure mercury, at a time when he could not bring the revived mercury 

 lower than 300 degrees : but this he would, till further trials have been made, 

 not have considered as a general axiom. 



From these experiments our author conceives it demonstrated, that heat alone 

 is the cause of the fluidity of mercury, as it is that of water and other fluids. If 

 therefore any part of the world does exist, in which so great a degree of cold 

 prevails, as to make mercury solid, there is no doubt but that mercury ought to 

 appear there as a body equally firm and consistent, as the rest of the metals do 

 here ; that mercury, on congealing, becomes its own ice, however difl^erent the 

 mercurial ice may be from that of water, or other liquids. The idea of freezing 

 does or can comprehend nothing more than a transition of bodies from a state of 

 fluidity to that of firmness, by the sole interposition of cold. The ice of oily and 

 saline bodies differs greatly from that of water, which is friable and easily broken, 

 whereas that of mercury is ductile. And M. Braun proceeds to consider all 

 bodies, which liquify by heat, as so many species of ice ; so that every metal, wax, 

 tallow, and glass, comes within his view in this respect. 



Mercury then is, in its natural state, a solid metal ; but is fusible in a very 

 small degree of heat. Every metal begins to flow in a certain degree of heat ; 

 but this degree is different in different metals. Pure tin begins to run at 420 ; 

 lead, at 530; and bismuth, at 470, in Fahrenheit's thermometer: or, according 

 to our author, lead liquifies at 320 above the cypher in his scale, which corres- 

 ponds with 596 in Fahrenheit; lead at 170=41 6 of Fahrenheit ; bismuth at 

 235=494 ; zinc requires a greater heat to melt it than will make mercury boil. 

 Now, if it could be settled, at what point mercury would begin to be congealed, 

 we should know the point at which it began to flow ; as it has been long known, 

 that water is either fluid or solid, as the heat of it is a very few degrees above or 

 under 32 in Fahrenheit's thermometer. Just so metals become solid at almost 

 the same degree of heat in which they become fluid. But in mercury, the con- 

 gealing point is at too great a latitude to be exactly determined : but our author 

 estimates it to be about 469 degrees in his thermometer ; at a less degree than 

 which, he has not been able to observe the slightest congealation. Hence it fol- 

 lows, that the condensation or contraction, and consequently the diminution of 

 the volume of mercury, must be very great indeed. This is demonstrated by the 

 great descent of the mercury in the thermometer while it is freezing. But how 

 great this diminution of the volume of the mercury is, cannot exactly be deter 



