524 Philofobhkal Netos. 



The only experiment he made on the fubjeft, was merely to ihew that a pendulum can 

 be made in this manner, which fliall vibrate quicker in a denfe medium, than in one more 

 rare, contrary to what takes place with common pendulums. 



He made a compound pendulum on the above principles, of about one foot in Its whole 

 length. This pendulum, on many trials, made In the air 57 vibrations in a minute. On 

 immerfing the whole in water, it made 59 vibrations in the fame time ; (hewing evidently, 

 that its returns were quicker in fo denfe a medium as water, than in the air. When the 

 lower bob or pendulum only was plunged in water, it made no more than 44 vibrations 

 in a minute. • 



DiJiiUatlon by the Application of the cooling Mixture. 



Mr. C. Wiftar, who In the third volume of the American Tranfadllons defcribed the 

 produftion of a vifible vapor from ice, at the melting point, fufpended in air reduced to the 

 temperature of o Fahrenheit; which he confidered as the confequence of a general law of 

 nature, has made fomc more experiments in illuftration of the fame law *. 



The inference, or law which he drew from thofe fads was, that the non-claftic vapor 

 does not depend upon any pofitive quantity or degree of fenCble heat in the evaporating 

 body, but upon a relative degree, exceeding that of the atmofphere to which it is expofed ; 

 and that it is produced by the paflage of heat from the moid body into the contiguous air. 

 If this theory be true, he Hates as a confequence, that a flow diftillation may be performed 

 with the common apparatus by applying cold to the receiver or refrigeratory, without 

 increafing the heat of the retort, or fubftance to be diftilled, as there will be a continual 

 paflage of heat from the body, to be evaporated or diftilled into the air of the receiver. 



He fubmitted this conclufion to the teft of experiment, becaufe It had been fuggcfted, 

 that the vapor which appeared to arlfe from ice, might have arifen from the mixture of 

 difi"erent portions of air of different temperatures; whereas by diftilling and evaporating 

 in a luted retort and receiver, there can be no mixture of warm and cold air; and by ufing 

 3 fubftance which is not contained in the atmofphere, all fufpiclon muft be removed of 

 the vapor itfelf having arifen from the included air. 



With views of this kind he poured an ounce and half of fulphuric ether into a retort, 

 and luted it to a receiver with a long neck, which was placed in a mixture of fait and fnow, 

 while the retort itfelf was furrounded by the common air at the temperature of 50" Fah- 

 renheit. The frigorific mixture was feldom lower than to', fo that the difference between 

 the temperatures of the two veffels did not exceed 40°. When the apparatus had been 

 thirty hours in this fituation, the frigorific mixture was removed, and one third of the 

 ether was found diftilled into the receiver. Another perfeftly fimilar apparatus and 

 charge, was expofed to the air at 50° for thirty hours, but without any application of the 

 freezing mixture. No diftillation took place. 



The former experiment was varied, by fubftituting camphor in the place of the ether. 

 The retort flood in air at 50°, and the receiver in the freezing mixture. At the end of 

 thirty hours, feme of the camphor was found to be fubllmed in the fame arborefcsnt form 

 as it ufuallyhas vi'hen produced by heat. 



♦ American Philof, Tranf. IV. 72. 



