188G.] on Properties common to Fluids and Solid Metals. 397 



be cooled down to —8^ Cent., without solidification, but agitation 



immediately determines the formation of ice, and at the same time a 



thermometer plunged in the water rises to zero. Faraday stated, in 



1858, that fused acetic acid, sulj)hur, phosphorus, many metals and 



many solutions,* would exhibit the same effect. 



Tin also may be cooled to several degrees below 



its solidifying point without actually freezing, 



and Dr. Van Eiemsdijk,"!' of Utrecht, has observed 



that a globule of gold or silver, in a fused state, 



will pass below its solidifying point without 



actually solidifying, but the slightest touch 



with a metallic point will cause the metal to 



solidify, and the consequent release of its latent 



heat of fusion is sufficient to raise the globule 



to the melting point again, as is indicated by 



a brilliant glow which the button emits, a beautiful effect which I 



hope to show you. [The exjDeriment was then made.] 



It may be well also to remind you incidentally that a minute 

 variation in composition is sometimes sufficient to lower the melting 

 point of a metal or alloy, as is instanced by the addition of y^- per 

 cent, of silicon to standard gold, which, as you will observe in the case 

 of this strip of the alloy, softens in the flame of a candle, or at about 

 the melting point of zinc, 412° Cent., although the melting point of 

 standard gold, free from silicon, would be over 1000^ Cent. 



Now to pass to solid metals. It is the common experience of us 

 all, that a counterfeit shilling, consisting j)rincipally of lead, does not 

 " ring " when thrown on a wooden surface. In 1726, Louis Lemery 

 observed that lead is under certain conditions almost as sonorous as 

 bell-metal. | He communicated the fact to l^eaumur, who, being 

 much struck by it, investigated the conditions under which lead 

 becomes sonorous, and submitted the results to the French Academy.§ 

 He pointed out that in describing a body which is not sonorous, it 

 is usual to say that it is as " dull as lead," an expression which has 

 become proverbial. " Nevertheless," he adds, " under certain con- 

 ditions, lead has a proj^erty both novel and remarkable, for it emits 

 surprisingly sharp notes when struck with another piece of lead." 

 He showed that it was necessary that the lead should be formed 

 by casting into a segment of a sphere, that is, mushroom shaped, as 

 in the sj)ecimens of lead exhibited. The lead must be free from 

 prominences, and must be neatly trimmed. The effect is less 

 marked, if the lead be very pure, than if ordinary commercial lead 

 be used, but it is only a question of degree. 



* Faraday, ' Experimental Researches in Chemistry and Physics,' p. 379. 

 t Dr. Van Rienisdijk, ' Ann. de Chim. et de Phys.' t. xx. 1880, p. 66. 

 X Hoefer, ' Histoire de la Chimie,' t. ii. p. 374. 



§ ' Histoire dc I'Academie Royale des Sciences,' Anne' 1726 [vol. for 1728. 

 V, 243]. 



