1869.] in liberating Vapour from Boiling Liquids. 249 



was instantaneous. Copious streams of bubbles proceeded from the filings, 

 the soubresauts ceased, and the temperature fell to 211|^°. Similar re- 

 sults were obtained with copper-filings, and copper and brass wire, clean 

 and unclean, and also with platinum foil and wire. 



An experiment with mercury may perhaps be of interest. The metal 

 was cleaned by being repeatedly shaken up with dilute nitric acid; and after 

 standing some time under it, a portion was drawn off from the bottom. 

 Five ounces of water in a clean flask boiled at 213-^J°. Enough mercury 

 was poured in to form a ring at the bottom of the flask. The water soon 

 regained its temperature, and even rose to 214°, with a good deal of bump- 

 ing — steam forming under the mercury and distending it into a large he- 

 misphere, which burst with a kick . The temperature varied between 213-^° 

 and 214°. It would have been dangerous to have entirely covered the 

 bottom with the metal ; for, as it was, the bursts of vapour were of an ex- 

 plosive character. While this uneasy boiling was going on, a very little 

 dirty mercury was added to the flask, and, although the quantity was not 

 more than one-sixth of that previously added, the effect was remarkable. 

 Instead of tbe uneasy, kicking, jerking bursts, the whole instantly changed 

 into a brisk, easy, soft boiling, rapid volleys of steam-balls being given off 

 by the metal, breaking up the mass of water, while the temperature re- 

 mained steady at 212^ -°. 



It will thus be seen that the vitreous and metallic bodies employed in 

 these experiments, as also the bits of paper, shavings of cedar-wood, &c, 

 are efficient as nuclei only so long as they are chemically unclean. When 

 clean they become inactive as "promoters of vaporization." 



Action of Porous Bodies. — But there are certain bodies, such as charcoal, 

 coke, &c, that I have not been able to make inactive, either by the action 

 of strong sulphuric or nitric acid, or by repeated boiling in water, ether, 

 spirits of wine, naphtha, &c. The same piece of charcoal held in the flame 

 of a spirit-lamp and then put into soda-water, or into a liquid at or near the 

 boiling-point, will liberate gas or vapour without any apparent diminution 

 of its powers. It may be transferred from one liquid to another, from 

 ether to alcohol, from alcohol to water, and from water to oil of turpentine 

 without ceasing to perform useful work in setting vapour free, making the 

 ooiling soft and easy, and preventing soubresauts* . The same remark ap- 

 plies to coke. It may be cleaned in the strongest acids, washed in water 

 and alkalies without losing any of its vigour as a liberator of vapour from 

 a hot liquid. It is quite remarkable to see how efficiently a lump of coke 

 acts in a vessel of boiling water in giving off vapour, promoting tranquil 

 boiling, and preventing the jumping of the vessel. Platinum sponge 

 is also active. A small piece of this substance at the bottom of a flask of 

 boiling water will send up vigorous jets of steam-bubbles, raising the water 



* Box-wood charcoal, which Saussure found so efficacious in his experiments on the 

 absorption of gases, is very active in boiling liquids : but specimens of charcoal and of 

 charcoal-bark from the softer wood are also of untiring activity. 



VOL.. XVII. T 



