148 Miscellaneous Intelligence, 



force in a metallic wire joining the two poles of a voltaic pile, is 

 constant for all points of the wire. 



II. Chemical Science. 



1. Variation of Boiling Points — Increased Production of Va" 

 •pour. — It has been known for some time that when certain kinds 

 of extraneous substances are introduced into boiling fluids, con- 

 siderable effect is produced upon the boiling point, vapour being 

 formed either at lower points or with much increased facility. Thus 

 Gay-Lussac has shewn that metal filings thrown into water, heated 

 in a glass vessel, lowers the boiling point of the water 2° or 3°, 

 and Mr. South pointed out the effect produced by putting platina 

 wire or slips of platina foil into hot sulphuric acid, causing it to 

 boil readily, quietly, and at lower points in glass vessels, than it 

 otherwise would do, the difference here being several degrees. 



Dr. Bostock has observed a remarkable fact of this kind in the 

 extent to which the boiling point of ether may be changed by the 

 introduction of a small chip of wood, or a portion of quill or 

 feather of any kind. Ether, in a glass vessel, boiled freely at 

 112°, and with difficulty at 1 10°. Employing another glass vessel, 

 it would not boil till the temperature had attained 150*, and the 

 latter point was retained in other vessels. Repeating the experi- 

 ment in a new vessel, it boiled earlier than before, but the vapour 

 was observed to come off from one point where some substance 

 had adhered to the glass. This led to the introduction of a small 

 cedar chip, when the wood was quickly covered with bubbles, and 

 the ether brought rapidly into ebullition. In this way ether boiled 

 at 102®, which, without the wood, required 150». The wood was not 

 so effectual after some time as at first. When completely soaked 

 with the ether it sunk to the bottom, and the ebullition nearly 

 ceased ; a fresh piece renewed it. Fragments of broken glass 

 lowered the boiling point considerably. A small piece of me- 

 tallic wire or copper filing, put into ether at 145°, caused a sudden 

 and copious explosion of gas or vapour, and lowered the boiling 

 point many degrees. Plunging a thermometer into the hot ether, 

 caused production of bubbles at a temperature many degrees be- 

 low the boiling point, no thermometer being present ; after a time 

 the effect ceased, but removal of the thermometer from the ether, 

 and then re-immersion of it, produced a repetition of the effect. 

 The cedar wood acted best when perfectly dry. 



Alcohol of S.G. .848, boiled in a glass vessel at 182°, but by 

 dropping in successive pieces of cedar wood the boiling point was 

 reduced as much as 30° and 40°. The boiling point of water. Dr. 

 Bostock found, was altered. 4° or 5° by chips of cedar wood, re- 

 quiring a temperature of about 217° when heated in a glass tube, 

 by means of hot brine, but being brought down to the usual boil- 

 ing point by the chips,— 4?iw, Phil iV. S, ix. 196. 



