﻿86 Dr. L. Bleekrode on some Experiments 



When the disk of carbon dioxide is not very compact, no 

 sound is produced, because the gas can escape in different 

 ways through the little spaces left, otherwise the intensity of 

 the sound is dependent on the conductivity for heat of the 

 substance brought in contact. 



A silver coin, when touching the disk with the flat side, 

 does not act, because it is uneven and little interstices are left, 

 otherwise silver emits loud sounds, and so it is with copper, 

 iron, aluminium ; lead produces a dull note and bismuth none at 

 all, as being a very bad conductor unless it has been heated, and 

 then it sounds only for a moment. The carbon rods used in 

 electric lamps remained silent, and also wood, but quartz and 

 rock-salt gave an audible note when a lens of compressed 

 carbon dioxide was applied on them with some pressure. 

 Very beautiful sounds, of the character of those produced 

 with the Trevelyan instrument, were heard when an iron rod 

 Was resting with one end on a horizontal cylinder of the 

 compact solid substance and touching with the other a glass 

 plate. 



As the escaping gas is the determining cause in all these 

 cases, it is to be expected that other substances, when capable 

 of rapid evaporation, on touching heated metals will also 

 emit sound, and indeed 1 obtained this very loud when a 

 brass sphere brought to incandescence was firmly pushed 

 down on a piece of mercury bichloride or camphor, and 

 especially on sal-ammoniac, all substances subliming at a red 

 heat ; accordingly dense vapours are evolved, when the metal 

 came in contact, and sounded on perforating them. 



Crystallization of Mercury. — Though the freezing of this 

 liquid metal with the mixture of solid carbon dioxide and 

 sulphuric ether is easily effected, crystallization is not apparent, 

 as the metal then solidifies too quickly. On trying the pro- 

 duction of sound with this liquid, I found a very effective 

 : method to obtain it crystallized. A disk of slightly com- 

 pressed carbon dioxide with a cavity was used, and still better 

 was a little cup, 4 centim. high, such as could be formed in 

 a convenient mould of wood, and this I filled with mercury, 

 just as a crucible. A low and distinct sound was given off', 

 and very regular undulations appeared on the bright metal 

 surface, indicating the pulsations provoked by the escaping 

 gas. Though the mercury does not actually touch the sides 

 of the cup (or the cavity on the disk) as a gas layer keeps it 

 away, yet its heat is dispersed by radiation towards the 

 extremely cold surrounding matter, and gradually the vibra- 

 tions cease. If at this moment the cup is emptied of its 

 still liquid contents, it is seen to be covered inside with 



