«54 ^^' Marcet's Experiments ott the Production of Cold 



haustion proceeds, and in one or two minutes it descends 

 from + 70" to — 7^** or even 80" of Fahrenheit's scale, 

 that is at least 40 degrees below the freezing point of mer- 

 cury. A cold of — 65 or — 70 is easily obtained by ex- 

 hausting the receiver till the rarefied air supports only one 

 quarter of an inch of mercury ; but with a pump capable of 

 exhausting to one-eighth of an inch, the thermometer sinks to 

 — 81° or 82* in less than two minutes. It is scarcely necessary 

 to observe that, if instead of a spirit thermometer, a tube con- 

 taining mercury be employed, this metal may be instantly 

 frozen, and the remarkable contraction, which it undergoes 

 at the moment of its congelation, may be seen and estimated 

 with great facility.* 



These experiments are but slightly influenced either by the 

 temperature of the atmosphere, or by that of the sulphureous 

 liquor ; but if the air be very damp, the moisture which accu- 

 mulates upon the bulb whilst cooling, slightly impedes the 

 process. This moisture appears in the form of a hoar frost, 

 forming a snowy arborescent deposition all over the covering 

 of the bulb. The oily liquor itself does not freeze when ex- 

 posed to a temperature of at least — 60". 



I shall not take up the time of the Society by a detail of the 

 various attempts which I have made to increase still farther 



vapour. It may be observed also, that the elastic force of the vapour of alcohol of 

 sulphur was stated by Mr. Berzelius and myself, in our joint paper, to be only 

 7,36 inches, instead of 10,75 ; but this difference is accounted for from the circum- 

 stance of the temperature, which in that instance was 53,5", instead of 66°; a differ- 

 ence which is very nearly that which might have been expected from a comparison 

 ivith the force of ether at the same temperature as given in Mr. Dalton's tables. 



• Mercury may also be fjozen by a similar process, by means of ether, as I have 

 stated ill Nicholson's Journal fur February last. 



